Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

722 files changed, 177485 insertions, 0 deletions

diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
new file mode 100644
index 000000000000..72dc90f8f4a7
--- /dev/null
+++ b/Documentation/00-INDEX
@@ -0,0 +1,294 @@
+
+This is a brief list of all the files in ./linux/Documentation and what
+they contain. If you add a documentation file, please list it here in
+alphabetical order as well, or risk being hunted down like a rabid dog.
+Please try and keep the descriptions small enough to fit on one line.
+							 Thanks -- Paul G.
+
+Following translations are available on the WWW:
+
+   - Japanese, maintained by the JF Project (JF@linux.or.jp), at
+     http://www.linux.or.jp/JF/
+
+00-INDEX
+	- this file.
+BK-usage/
+	- directory with info on BitKeeper.
+BUG-HUNTING
+	- brute force method of doing binary search of patches to find bug.
+Changes
+	- list of changes that break older software packages.
+CodingStyle
+	- how the boss likes the C code in the kernel to look.
+DMA-API.txt
+	- DMA API, pci_ API & extensions for non-consistent memory machines.
+DMA-mapping.txt
+	- info for PCI drivers using DMA portably across all platforms.
+DocBook/
+	- directory with DocBook templates etc. for kernel documentation.
+IO-mapping.txt
+	- how to access I/O mapped memory from within device drivers.
+IPMI.txt
+	- info on Linux Intelligent Platform Management Interface (IPMI) Driver.
+IRQ-affinity.txt
+	- how to select which CPU(s) handle which interrupt events on SMP.
+ManagementStyle
+	- how to (attempt to) manage kernel hackers.
+MSI-HOWTO.txt
+	- the Message Signaled Interrupts (MSI) Driver Guide HOWTO and FAQ.
+RCU/
+	- directory with info on RCU (read-copy update).
+README.DAC960
+	- info on Mylex DAC960/DAC1100 PCI RAID Controller Driver for Linux.
+SAK.txt
+	- info on Secure Attention Keys.
+SubmittingDrivers
+	- procedure to get a new driver source included into the kernel tree.
+SubmittingPatches
+	- procedure to get a source patch included into the kernel tree.
+VGA-softcursor.txt
+	- how to change your VGA cursor from a blinking underscore.
+arm/
+	- directory with info about Linux on the ARM architecture.
+basic_profiling.txt
+	- basic instructions for those who wants to profile Linux kernel.
+binfmt_misc.txt
+	- info on the kernel support for extra binary formats.
+block/
+	- info on the Block I/O (BIO) layer.
+cachetlb.txt
+	- describes the cache/TLB flushing interfaces Linux uses.
+cciss.txt
+	- info, major/minor #'s for Compaq's SMART Array Controllers.
+cdrom/
+	- directory with information on the CD-ROM drivers that Linux has.
+cli-sti-removal.txt
+	- cli()/sti() removal guide.
+computone.txt
+	- info on Computone Intelliport II/Plus Multiport Serial Driver.
+cpqarray.txt
+	- info on using Compaq's SMART2 Intelligent Disk Array Controllers.
+cpu-freq/
+	- info on CPU frequency and voltage scaling.
+cris/
+	- directory with info about Linux on CRIS architecture.
+crypto/
+	- directory with info on the Crypto API.
+debugging-modules.txt
+	- some notes on debugging modules after Linux 2.6.3.
+device-mapper/
+	- directory with info on Device Mapper.
+devices.txt
+	- plain ASCII listing of all the nodes in /dev/ with major minor #'s.
+digiepca.txt
+	- info on Digi Intl. {PC,PCI,EISA}Xx and Xem series cards.
+dnotify.txt
+	- info about directory notification in Linux.
+driver-model/
+	- directory with info about Linux driver model.
+dvb/
+	- info on Linux Digital Video Broadcast (DVB) subsystem.
+early-userspace/
+	- info about initramfs, klibc, and userspace early during boot.
+eisa.txt
+	- info on EISA bus support.
+exception.txt
+	- how Linux v2.2 handles exceptions without verify_area etc.
+fb/
+	- directory with info on the frame buffer graphics abstraction layer.
+filesystems/
+	- directory with info on the various filesystems that Linux supports.
+firmware_class/
+	- request_firmware() hotplug interface info.
+floppy.txt
+	- notes and driver options for the floppy disk driver.
+ftape.txt
+	- notes about the floppy tape device driver.
+hayes-esp.txt
+	- info on using the Hayes ESP serial driver.
+highuid.txt
+	- notes on the change from 16 bit to 32 bit user/group IDs.
+hpet.txt
+	- High Precision Event Timer Driver for Linux.
+hw_random.txt
+	- info on Linux support for random number generator in i8xx chipsets.
+i2c/
+	- directory with info about the I2C bus/protocol (2 wire, kHz speed).
+i2o/
+	- directory with info about the Linux I2O subsystem.
+i386/
+	- directory with info about Linux on Intel 32 bit architecture.
+ia64/
+	- directory with info about Linux on Intel 64 bit architecture.
+ide.txt
+	- important info for users of ATA devices (IDE/EIDE disks and CD-ROMS).
+initrd.txt
+	- how to use the RAM disk as an initial/temporary root filesystem.
+input/
+	- info on Linux input device support.
+io_ordering.txt
+	- info on ordering I/O writes to memory-mapped addresses.
+ioctl-number.txt
+	- how to implement and register device/driver ioctl calls.
+iostats.txt
+	- info on I/O statistics Linux kernel provides.
+isapnp.txt
+	- info on Linux ISA Plug & Play support.
+isdn/
+	- directory with info on the Linux ISDN support, and supported cards.
+java.txt
+	- info on the in-kernel binary support for Java(tm).
+kbuild/
+	- directory with info about the kernel build process.
+kernel-doc-nano-HOWTO.txt
+	- mini HowTo on generation and location of kernel documentation files.
+kernel-docs.txt
+	- listing of various WWW + books that document kernel internals.
+kernel-parameters.txt
+	- summary listing of command line / boot prompt args for the kernel.
+kobject.txt
+	- info of the kobject infrastructure of the Linux kernel.
+laptop-mode.txt
+	- How to conserve battery power using laptop-mode.
+ldm.txt
+	- a brief description of LDM (Windows Dynamic Disks).
+locks.txt
+	- info on file locking implementations, flock() vs. fcntl(), etc.
+logo.gif
+	- Full colour GIF image of Linux logo (penguin).
+logo.txt
+	- Info on creator of above logo & site to get additional images from.
+m68k/
+	- directory with info about Linux on Motorola 68k architecture.
+magic-number.txt
+	- list of magic numbers used to mark/protect kernel data structures.
+mandatory.txt
+	- info on the Linux implementation of Sys V mandatory file locking.
+mca.txt
+	- info on supporting Micro Channel Architecture (e.g. PS/2) systems.
+md.txt
+	- info on boot arguments for the multiple devices driver.
+memory.txt
+	- info on typical Linux memory problems.
+mips/
+	- directory with info about Linux on MIPS architecture.
+mono.txt
+	- how to execute Mono-based .NET binaries with the help of BINFMT_MISC.
+moxa-smartio
+	- info on installing/using Moxa multiport serial driver.
+mtrr.txt
+	- how to use PPro Memory Type Range Registers to increase performance.
+nbd.txt
+	- info on a TCP implementation of a network block device.
+networking/
+	- directory with info on various aspects of networking with Linux.
+nfsroot.txt
+	- short guide on setting up a diskless box with NFS root filesystem.
+nmi_watchdog.txt
+	- info on NMI watchdog for SMP systems.
+numastat.txt
+	- info on how to read Numa policy hit/miss statistics in sysfs.
+oops-tracing.txt
+	- how to decode those nasty internal kernel error dump messages.
+paride.txt
+	- information about the parallel port IDE subsystem.
+parisc/
+	- directory with info on using Linux on PA-RISC architecture.
+parport.txt
+	- how to use the parallel-port driver.
+parport-lowlevel.txt
+	- description and usage of the low level parallel port functions.
+pci.txt
+	- info on the PCI subsystem for device driver authors.
+pm.txt
+	- info on Linux power management support.
+pnp.txt
+	- Linux Plug and Play documentation.
+power/
+	- directory with info on Linux PCI power management.
+powerpc/
+	- directory with info on using Linux with the PowerPC.
+preempt-locking.txt
+	- info on locking under a preemptive kernel.
+ramdisk.txt
+	- short guide on how to set up and use the RAM disk.
+riscom8.txt
+	- notes on using the RISCom/8 multi-port serial driver.
+rocket.txt
+	- info on the Comtrol RocketPort multiport serial driver.
+rpc-cache.txt
+	- introduction to the caching mechanisms in the sunrpc layer.
+rtc.txt
+	- notes on how to use the Real Time Clock (aka CMOS clock) driver.
+s390/
+	- directory with info on using Linux on the IBM S390.
+sched-coding.txt
+	- reference for various scheduler-related methods in the O(1) scheduler.
+sched-design.txt
+	- goals, design and implementation of the Linux O(1) scheduler.
+sched-domains.txt
+	- information on scheduling domains.
+sched-stats.txt
+	- information on schedstats (Linux Scheduler Statistics).
+scsi/
+	- directory with info on Linux scsi support.
+serial/
+	- directory with info on the low level serial API.
+serial-console.txt
+	- how to set up Linux with a serial line console as the default.
+sgi-visws.txt
+	- short blurb on the SGI Visual Workstations.
+sh/
+	- directory with info on porting Linux to a new architecture.
+smart-config.txt
+	- description of the Smart Config makefile feature.
+smp.txt
+	- a few notes on symmetric multi-processing.
+sonypi.txt
+	- info on Linux Sony Programmable I/O Device support.
+sound/
+	- directory with info on sound card support.
+sparc/
+	- directory with info on using Linux on Sparc architecture.
+specialix.txt
+	- info on hardware/driver for specialix IO8+ multiport serial card.
+spinlocks.txt
+	- info on using spinlocks to provide exclusive access in kernel.
+stallion.txt
+	- info on using the Stallion multiport serial driver.
+svga.txt
+	- short guide on selecting video modes at boot via VGA BIOS.
+sx.txt
+	- info on the Specialix SX/SI multiport serial driver.
+sysctl/
+	- directory with info on the /proc/sys/* files.
+sysrq.txt
+	- info on the magic SysRq key.
+telephony/
+	- directory with info on telephony (e.g. voice over IP) support.
+time_interpolators.txt
+	- info on time interpolators.
+tipar.txt
+	- information about Parallel link cable for Texas Instruments handhelds.
+tty.txt
+	- guide to the locking policies of the tty layer.
+unicode.txt
+	- info on the Unicode character/font mapping used in Linux.
+uml/
+	- directory with infomation about User Mode Linux.
+usb/
+	- directory with info regarding the Universal Serial Bus.
+video4linux/
+	- directory with info regarding video/TV/radio cards and linux.
+vm/
+	- directory with info on the Linux vm code.
+voyager.txt
+	- guide to running Linux on the Voyager architecture.
+watchdog/
+	- how to auto-reboot Linux if it has "fallen and can't get up". ;-)
+x86_64/
+	- directory with info on Linux support for AMD x86-64 (Hammer) machines.
+xterm-linux.xpm
+	- XPM image of penguin logo (see logo.txt) sitting on an xterm.
+zorro.txt
+	- info on writing drivers for Zorro bus devices found on Amigas.
diff --git a/Documentation/BK-usage/00-INDEX b/Documentation/BK-usage/00-INDEX
new file mode 100644
index 000000000000..82768784ea52
--- /dev/null
+++ b/Documentation/BK-usage/00-INDEX
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+bk-kernel-howto.txt: Description of kernel workflow under BitKeeper
+
+bk-make-sum: Create summary of changesets in one repository and not
+another, typically in preparation to be sent to an upstream maintainer.
+Typical usage:
+	cd my-updated-repo
+	bk-make-sum ~/repo/original-repo
+	mv /tmp/linus.txt ../original-repo.txt
+
+bksend: Create readable text output containing summary of changes, GNU
+patch of the changes, and BK metadata of changes (as needed for proper
+importing into BitKeeper by an upstream maintainer).  This output is
+suitable for emailing BitKeeper changes.  The recipient of this output
+may pipe it directly to 'bk receive'.
+
+bz64wrap: helper script. Uncompressed input is piped to this script,
+which compresses its input, and then outputs the uu-/base64-encoded
+version of the compressed input.
+
+cpcset: Copy changeset between unrelated repositories.
+Attempts to preserve changeset user, user address, description, in
+addition to the changeset (the patch) itself.
+Typical usage:
+	cd my-updated-repo
+	bk changes	# looking for a changeset...
+	cpcset 1.1511 . ../another-repo
+
+csets-to-patches: Produces a delta of two BK repositories, in the form
+of individual files, each containing a single cset as a GNU patch.
+Output is several files, each with the filename "/tmp/rev-$REV.patch"
+Typical usage:
+	cd my-updated-repo
+	bk changes -L ~/repo/original-repo 2>&1 | \
+		perl csets-to-patches
+
+cset-to-linus: Produces a delta of two BK repositories, in the form of
+changeset descriptions, with 'diffstat' output created for each
+individual changset.
+Typical usage:
+	cd my-updated-repo
+	bk changes -L ~/repo/original-repo 2>&1 | \
+		perl cset-to-linus > summary.txt
+
+gcapatch:  Generates patch containing changes in local repository.
+Typical usage:
+	cd my-updated-repo
+	gcapatch > foo.patch
+
+unbz64wrap: Reverse an encoded, compressed data stream created by
+bz64wrap into an uncompressed, typically text/plain output.
+
diff --git a/Documentation/BK-usage/bk-kernel-howto.txt b/Documentation/BK-usage/bk-kernel-howto.txt
new file mode 100644
index 000000000000..b7b9075d2910
--- /dev/null
+++ b/Documentation/BK-usage/bk-kernel-howto.txt
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+
+		   Doing the BK Thing, Penguin-Style
+
+
+
+
+This set of notes is intended mainly for kernel developers, occasional
+or full-time, but sysadmins and power users may find parts of it useful
+as well.  It assumes at least a basic familiarity with CVS, both at a
+user level (use on the cmd line) and at a higher level (client-server model).
+Due to the author's background, an operation may be described in terms
+of CVS, or in terms of how that operation differs from CVS.
+
+This is -not- intended to be BitKeeper documentation.  Always run
+"bk help <command>" or in X "bk helptool <command>" for reference
+documentation.
+
+
+BitKeeper Concepts
+------------------
+
+In the true nature of the Internet itself, BitKeeper is a distributed
+system.  When applied to revision control, this means doing away with
+client-server, and changing to a parent-child model... essentially
+peer-to-peer.  On the developer's end, this also represents a
+fundamental disruption in the standard workflow of changes, commits,
+and merges.  You will need to take a few minutes to think about
+how to best work under BitKeeper, and re-optimize things a bit.
+In some sense it is a bit radical, because it might described as
+tossing changes out into a maelstrom and having them magically
+land at the right destination... but I'm getting ahead of myself.
+
+Let's start with this progression:
+Each BitKeeper source tree on disk is a repository unto itself.
+Each repository has a parent (except the root/original, of course).
+Each repository contains a set of a changesets ("csets").
+Each cset is one or more changed files, bundled together.
+
+Each tree is a repository, so all changes are checked into the local
+tree.  When a change is checked in, all modified files are grouped
+into a logical unit, the changeset.  Internally, BK links these
+changesets in a tree, representing various converging and diverging
+lines of development.  These changesets are the bread and butter of
+the BK system.
+
+After the concept of changesets, the next thing you need to get used
+to is having multiple copies of source trees lying around.  This -really-
+takes some getting used to, for some people.  Separate source trees
+are the means in BitKeeper by which you delineate parallel lines
+of development, both minor and major.  What would be branches in
+CVS become separate source trees, or "clones" in BitKeeper [heh,
+or Star Wars] terminology.
+
+Clones and changesets are the tools from which most of the power of
+BitKeeper is derived.  As mentioned earlier, each clone has a parent,
+the tree used as the source when the new clone was created.  In a
+CVS-like setup, the parent would be a remote server on the Internet,
+and the child is your local clone of that tree.
+
+Once you have established a common baseline between two source trees --
+a common parent -- then you can merge changesets between those two
+trees with ease.  Merging changes into a tree is called a "pull", and
+is analagous to 'cvs update'.  A pull downloads all the changesets in
+the remote tree you do not have, and merges them.  Sending changes in
+one tree to another tree is called a "push".  Push sends all changes
+in the local tree the remote does not yet have, and merges them.
+
+From these concepts come some initial command examples:
+
+1) bk clone -q http://linux.bkbits.net/linux-2.5 linus-2.5
+Download a 2.5 stock kernel tree, naming it "linus-2.5" in the local dir.
+The "-q" disables listing every single file as it is downloaded.
+
+2) bk clone -ql linus-2.5 alpha-2.5
+Create a separate source tree for the Alpha AXP architecture.
+The "-l" uses hard links instead of copying data, since both trees are
+on the local disk.  You can also replace the above with "bk lclone -q ..."
+
+You only clone a tree -once-.  After cloning the tree lives a long time
+on disk, being updating by pushes and pulls.
+
+3) cd alpha-2.5 ; bk pull http://gkernel.bkbits.net/alpha-2.5
+Download changes in "alpha-2.5" repository which are not present
+in the local repository, and merge them into the source tree.
+
+4) bk -r co -q
+Because every tree is a repository, files must be checked out before
+they will be in their standard places in the source tree.
+
+5)	bk vi fs/inode.c				# example change...
+	bk citool					# checkin, using X tool
+	bk push bk://gkernel@bkbits.net/alpha-2.5	# upload change
+Typical example of a BK sequence that would replace the analagous CVS
+situation,
+	vi fs/inode.c
+	cvs commit
+
+As this is just supposed to be a quick BK intro, for more in-depth
+tutorials, live working demos, and docs, see http://www.bitkeeper.com/
+
+
+
+BK and Kernel Development Workflow
+----------------------------------
+Currently the latest 2.5 tree is available via "bk clone $URL"
+and "bk pull $URL" at http://linux.bkbits.net/linux-2.5
+This should change in a few weeks to a kernel.org URL.
+
+
+A big part of using BitKeeper is organizing the various trees you have
+on your local disk, and organizing the flow of changes among those
+trees, and remote trees.  If one were to graph the relationships between
+a desired BK setup, you are likely to see a few-many-few graph, like
+this:
+
+		    linux-2.5
+		        |
+	       merge-to-linus-2.5
+		 /    |      |
+	        /     |      |
+	vm-hacks  bugfixes  filesys   personal-hacks
+	      \	      |	     |		/
+	       \      |      |         /
+		\     |      |        /
+	         testing-and-validation
+
+Since a "bk push" sends all changes not in the target tree, and
+since a "bk pull" receives all changes not in the source tree, you want
+to make sure you are only pushing specific changes to the desired tree,
+not all changes from "peer parent" trees.  For example, pushing a change
+from the testing-and-validation tree would probably be a bad idea,
+because it will push all changes from vm-hacks, bugfixes, filesys, and
+personal-hacks trees into the target tree.
+
+One would typically work on only one "theme" at a time, either
+vm-hacks or bugfixes or filesys, keeping those changes isolated in
+their own tree during development, and only merge the isolated with
+other changes when going upstream (to Linus or other maintainers) or
+downstream (to your "union" trees, like testing-and-validation above).
+
+It should be noted that some of this separation is not just recommended
+practice, it's actually [for now] -enforced- by BitKeeper.  BitKeeper
+requires that changesets maintain a certain order, which is the reason
+that "bk push" sends all local changesets the remote doesn't have.  This
+separation may look like a lot of wasted disk space at first, but it
+helps when two unrelated changes may "pollute" the same area of code, or
+don't follow the same pace of development, or any other of the standard
+reasons why one creates a development branch.
+
+Small development branches (clones) will appear and disappear:
+
+	-------- A --------- B --------- C --------- D -------
+	          \                                 /
+		   -----short-term devel branch-----
+
+While long-term branches will parallel a tree (or trees), with period
+merge points.  In this first example, we pull from a tree (pulls,
+"\") periodically, such as what occurs when tracking changes in a
+vendor tree, never pushing changes back up the line:
+
+	-------- A --------- B --------- C --------- D -------
+	          \                       \           \
+	           ----long-term devel branch-----------------
+
+And then a more common case in Linux kernel development, a long term
+branch with periodic merges back into the tree (pushes, "/"):
+
+	-------- A --------- B --------- C --------- D -------
+	          \                       \         / \
+	           ----long-term devel branch-----------------
+
+
+
+
+
+Submitting Changes to Linus
+---------------------------
+There's a bit of an art, or style, of submitting changes to Linus.
+Since Linus's tree is now (you might say) fully integrated into the
+distributed BitKeeper system, there are several prerequisites to
+properly submitting a BitKeeper change.  All these prereq's are just
+general cleanliness of BK usage, so as people become experts at BK, feel
+free to optimize this process further (assuming Linus agrees, of
+course).
+
+
+
+0) Make sure your tree was originally cloned from the linux-2.5 tree
+created by Linus.  If your tree does not have this as its ancestor, it
+is impossible to reliably exchange changesets.
+
+
+
+1) Pay attention to your commit text.  The commit message that
+accompanies each changeset you submit will live on forever in history,
+and is used by Linus to accurately summarize the changes in each
+pre-patch.  Remember that there is no context, so
+	"fix for new scheduler changes"
+would be too vague, but
+	"fix mips64 arch for new scheduler switch_to(), TIF_xxx semantics"
+would be much better.
+
+You can and should use the command "bk comment -C<rev>" to update the
+commit text, and improve it after the fact.  This is very useful for
+development: poor, quick descriptions during development, which get
+cleaned up using "bk comment" before issuing the "bk push" to submit the
+changes.
+
+
+
+2) Include an Internet-available URL for Linus to pull from, such as
+
+	Pull from:  http://gkernel.bkbits.net/net-drivers-2.5
+
+
+
+3) Include a summary and "diffstat -p1" of each changeset that will be
+downloaded, when Linus issues a "bk pull".  The author auto-generates
+these summaries using "bk changes -L <parent>", to obtain a listing
+of all the pending-to-send changesets, and their commit messages.
+
+It is important to show Linus what he will be downloading when he issues
+a "bk pull", to reduce the time required to sift the changes once they
+are downloaded to Linus's local machine.
+
+IMPORTANT NOTE:  One of the features of BK is that your repository does
+not have to be up to date, in order for Linus to receive your changes.
+It is considered a courtesy to keep your repository fairly recent, to
+lessen any potential merge work Linus may need to do.
+
+
+4) Split up your changes.  Each maintainer<->Linus situation is likely
+to be slightly different here, so take this just as general advice.  The
+author splits up changes according to "themes" when merging with Linus.
+Simultaneous pushes from local development go to special trees which
+exist solely to house changes "queued" for Linus.  Example of the trees:
+
+	net-drivers-2.5 -- on-going net driver maintenance
+	vm-2.5 -- VM-related changes
+	fs-2.5 -- filesystem-related changes
+
+Linus then has much more freedom for pulling changes.  He could (for
+example) issue a "bk pull" on vm-2.5 and fs-2.5 trees, to merge their
+changes, but hold off net-drivers-2.5 because of a change that needs
+more discussion.
+
+Other maintainers may find that a single linus-pull-from tree is
+adequate for passing BK changesets to him.
+
+
+
+Frequently Answered Questions
+-----------------------------
+1) How do I change the e-mail address shown in the changelog?
+A. When you run "bk citool" or "bk commit", set environment
+   variables BK_USER and BK_HOST to the desired username
+   and host/domain name.
+
+
+2) How do I use tags / get a diff between two kernel versions?
+A. Pass the tags Linus uses to 'bk export'.
+
+ChangeSets are in a forward-progressing order, so it's pretty easy
+to get a snapshot starting and ending at any two points in time.
+Linus puts tags on each release and pre-release, so you could use
+these two examples:
+
+    bk export -tpatch -hdu -rv2.5.4,v2.5.5 | less
+        # creates patch-2.5.5 essentially
+    bk export -tpatch -du -rv2.5.5-pre1,v2.5.5 | less
+        # changes from pre1 to final
+
+A tag is just an alias for a specific changeset... and since changesets
+are ordered, a tag is thus a marker for a specific point in time (or
+specific state of the tree).
+
+
+3) Is there an easy way to generate One Big Patch versus mainline,
+   for my long-lived kernel branch?
+A. Yes.  This requires BK 3.x, though.
+
+	bk export -tpatch -r`bk repogca bk://linux.bkbits.net/linux-2.5`,+
+
diff --git a/Documentation/BK-usage/bk-make-sum b/Documentation/BK-usage/bk-make-sum
new file mode 100755
index 000000000000..58ca46a0fcc6
--- /dev/null
+++ b/Documentation/BK-usage/bk-make-sum
@@ -0,0 +1,34 @@
+#!/bin/sh -e
+# DIR=$HOME/BK/axp-2.5
+# cd $DIR
+
+LINUS_REPO=$1
+DIRBASE=`basename $PWD`
+
+{
+cat <<EOT
+Please do a
+
+	bk pull bk://gkernel.bkbits.net/$DIRBASE
+
+This will update the following files:
+
+EOT
+
+bk export -tpatch -hdu -r`bk repogca $LINUS_REPO`,+ | diffstat -p1 2>/dev/null
+
+cat <<EOT
+
+through these ChangeSets:
+
+EOT
+
+bk changes -L -d'$unless(:MERGE:){ChangeSet|:CSETREV:\n}' $LINUS_REPO |
+bk -R prs -h -d'$unless(:MERGE:){<:P:@:HOST:> (:D: :I:)\n$each(:C:){   (:C:)\n}\n}' -
+
+} > /tmp/linus.txt
+
+cat <<EOT
+Mail text in /tmp/linus.txt; please check and send using your favourite
+mailer.
+EOT
diff --git a/Documentation/BK-usage/bksend b/Documentation/BK-usage/bksend
new file mode 100755
index 000000000000..836ca943694f
--- /dev/null
+++ b/Documentation/BK-usage/bksend
@@ -0,0 +1,36 @@
+#!/bin/sh
+# A script to format BK changeset output in a manner that is easy to read.
+# Andreas Dilger <adilger@turbolabs.com>  13/02/2002
+#
+# Add diffstat output after Changelog <adilger@turbolabs.com>   21/02/2002
+
+PROG=bksend
+
+usage() {
+	echo "usage: $PROG -r<rev>"
+	echo -e "\twhere <rev> is of the form '1.23', '1.23..', '1.23..1.27',"
+	echo -e "\tor '+' to indicate the most recent revision"
+
+	exit 1
+}
+
+case $1 in
+-r) REV=$2; shift ;;
+-r*) REV=`echo $1 | sed 's/^-r//'` ;;
+*) echo "$PROG: no revision given, you probably don't want that";;
+esac
+
+[ -z "$REV" ] && usage
+
+echo "You can import this changeset into BK by piping this whole message to:"
+echo "'| bk receive [path to repository]' or apply the patch as usual."
+
+SEP="\n===================================================================\n\n"
+echo -e $SEP
+env PAGER=/bin/cat bk changes -r$REV
+echo
+bk export -tpatch -du -h -r$REV | diffstat
+echo; echo
+bk export -tpatch -du -h -r$REV
+echo -e $SEP
+bk send -wgzip_uu -r$REV -
diff --git a/Documentation/BK-usage/bz64wrap b/Documentation/BK-usage/bz64wrap
new file mode 100755
index 000000000000..be780876849f
--- /dev/null
+++ b/Documentation/BK-usage/bz64wrap
@@ -0,0 +1,41 @@
+#!/bin/sh
+
+# bz64wrap - the sending side of a bzip2 | base64 stream
+# Andreas Dilger <adilger@clusterfs.com>   Jan 2002
+
+
+PATH=$PATH:/usr/bin:/usr/local/bin:/usr/freeware/bin
+
+# A program to generate base64 encoding on stdout
+BASE64_ENCODE="uuencode -m /dev/stdout"
+BASE64_BEGIN=
+BASE64_END=
+
+BZIP=NO
+BASE64=NO
+
+# Test if we have the bzip program installed
+bzip2 -c /dev/null > /dev/null 2>&1 && BZIP=YES
+
+# Test if uuencode can handle the -m (MIME) encoding option
+$BASE64_ENCODE < /dev/null > /dev/null 2>&1 && BASE64=YES
+
+if [ $BASE64 = NO ]; then
+	BASE64_ENCODE=mimencode
+	BASE64_BEGIN="begin-base64 644 -"
+	BASE64_END="===="
+
+	$BASE64_ENCODE < /dev/null > /dev/null 2>&1 && BASE64=YES
+fi
+
+if [ $BZIP = NO -o $BASE64 = NO ]; then
+	echo "$0: can't use bz64 encoding: bzip2=$BZIP, $BASE64_ENCODE=$BASE64"
+	exit 1
+fi
+
+# Sadly, mimencode does not appear to have good "begin" and "end" markers
+# like uuencode does, and it is picky about getting the right start/end of
+# the base64 stream, so we handle this internally.
+echo "$BASE64_BEGIN"
+bzip2 -9 | $BASE64_ENCODE
+echo "$BASE64_END"
diff --git a/Documentation/BK-usage/cpcset b/Documentation/BK-usage/cpcset
new file mode 100755
index 000000000000..b8faca97dab9
--- /dev/null
+++ b/Documentation/BK-usage/cpcset
@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# Purpose: Copy changeset patch and description from one
+#	   repository to another, unrelated one.
+#
+# usage:  cpcset [revision] [from-repository] [to-repository]
+#
+
+REV=$1
+FROM=$2
+TO=$3
+TMPF=/tmp/cpcset.$$
+
+rm -f $TMPF*
+
+CWD_SAVE=`pwd`
+cd $FROM
+bk changes -r$REV			|	\
+	grep -v '^ChangeSet'		|	\
+	sed -e 's/^  //g' > $TMPF.log
+
+USERHOST=`bk changes -r$REV | grep '^ChangeSet' | awk '{print $4}'`
+export BK_USER=`echo $USERHOST | awk '-F@' '{print $1}'`
+export BK_HOST=`echo $USERHOST | awk '-F@' '{print $2}'`
+
+bk export -tpatch -hdu -r$REV > $TMPF.patch && \
+cd $CWD_SAVE && \
+cd $TO && \
+bk import -tpatch -CFR -y"`cat $TMPF.log`" $TMPF.patch . && \
+bk commit -y"`cat $TMPF.log`"
+
+rm -f $TMPF*
+
+echo changeset $REV copied.
+echo ""
+
diff --git a/Documentation/BK-usage/cset-to-linus b/Documentation/BK-usage/cset-to-linus
new file mode 100755
index 000000000000..d28a96f8c618
--- /dev/null
+++ b/Documentation/BK-usage/cset-to-linus
@@ -0,0 +1,49 @@
+#!/usr/bin/perl -w
+
+use strict;
+
+my ($lhs, $rev, $tmp, $rhs, $s);
+my @cset_text = ();
+my @pipe_text = ();
+my $have_cset = 0;
+
+while (<>) {
+	next if /^---/;
+
+	if (($lhs, $tmp, $rhs) = (/^(ChangeSet\@)([^,]+)(, .*)$/)) {
+		&cset_rev if ($have_cset);
+
+		$rev = $tmp;
+		$have_cset = 1;
+
+		push(@cset_text, $_);
+	}
+
+	elsif ($have_cset) {
+		push(@cset_text, $_);
+	}
+}
+&cset_rev if ($have_cset);
+exit(0);
+
+
+sub cset_rev {
+	my $empty_cset = 0;
+
+	open PIPE, "bk export -tpatch -hdu -r $rev | diffstat -p1 2>/dev/null |" or die;
+	while ($s = <PIPE>) {
+		$empty_cset = 1 if ($s =~ /0 files changed/);
+		push(@pipe_text, $s);
+	}
+	close(PIPE);
+
+	if (! $empty_cset) {
+		print @cset_text;
+		print @pipe_text;
+		print "\n\n";
+	}
+
+	@pipe_text = ();
+	@cset_text = ();
+}
+
diff --git a/Documentation/BK-usage/csets-to-patches b/Documentation/BK-usage/csets-to-patches
new file mode 100755
index 000000000000..e2b81c35883f
--- /dev/null
+++ b/Documentation/BK-usage/csets-to-patches
@@ -0,0 +1,44 @@
+#!/usr/bin/perl -w
+
+use strict;
+
+my ($lhs, $rev, $tmp, $rhs, $s);
+my @cset_text = ();
+my @pipe_text = ();
+my $have_cset = 0;
+
+while (<>) {
+	next if /^---/;
+
+	if (($lhs, $tmp, $rhs) = (/^(ChangeSet\@)([^,]+)(, .*)$/)) {
+		&cset_rev if ($have_cset);
+
+		$rev = $tmp;
+		$have_cset = 1;
+
+		push(@cset_text, $_);
+	}
+
+	elsif ($have_cset) {
+		push(@cset_text, $_);
+	}
+}
+&cset_rev if ($have_cset);
+exit(0);
+
+
+sub cset_rev {
+	my $empty_cset = 0;
+
+	system("bk export -tpatch -du -r $rev > /tmp/rev-$rev.patch");
+
+	if (! $empty_cset) {
+		print @cset_text;
+		print @pipe_text;
+		print "\n\n";
+	}
+
+	@pipe_text = ();
+	@cset_text = ();
+}
+
diff --git a/Documentation/BK-usage/gcapatch b/Documentation/BK-usage/gcapatch
new file mode 100755
index 000000000000..aaeb17dc7c7f
--- /dev/null
+++ b/Documentation/BK-usage/gcapatch
@@ -0,0 +1,8 @@
+#!/bin/sh
+#
+# Purpose: Generate GNU diff of local changes versus canonical top-of-tree
+#
+# Usage: gcapatch > foo.patch
+#
+
+bk export -tpatch -hdu -r`bk repogca bk://linux.bkbits.net/linux-2.5`,+
diff --git a/Documentation/BK-usage/unbz64wrap b/Documentation/BK-usage/unbz64wrap
new file mode 100755
index 000000000000..4fc3e73e9a81
--- /dev/null
+++ b/Documentation/BK-usage/unbz64wrap
@@ -0,0 +1,25 @@
+#!/bin/sh
+
+# unbz64wrap - the receiving side of a bzip2 | base64 stream
+# Andreas Dilger <adilger@clusterfs.com>   Jan 2002
+
+# Sadly, mimencode does not appear to have good "begin" and "end" markers
+# like uuencode does, and it is picky about getting the right start/end of
+# the base64 stream, so we handle this explicitly here.
+
+PATH=$PATH:/usr/bin:/usr/local/bin:/usr/freeware/bin
+
+if mimencode -u < /dev/null > /dev/null 2>&1 ; then
+	SHOW=
+	while read LINE; do
+		case $LINE in
+		begin-base64*) SHOW=YES ;;
+		====) SHOW= ;;
+		*) [ "$SHOW" ] && echo "$LINE" ;;
+		esac
+	done | mimencode -u | bunzip2
+	exit $?
+else
+	cat - | uudecode -o /dev/stdout | bunzip2
+	exit $?
+fi
diff --git a/Documentation/BUG-HUNTING b/Documentation/BUG-HUNTING
new file mode 100644
index 000000000000..ca29242dbc38
--- /dev/null
+++ b/Documentation/BUG-HUNTING
@@ -0,0 +1,92 @@
+[Sat Mar  2 10:32:33 PST 1996 KERNEL_BUG-HOWTO lm@sgi.com (Larry McVoy)]
+
+This is how to track down a bug if you know nothing about kernel hacking.  
+It's a brute force approach but it works pretty well.
+
+You need:
+
+        . A reproducible bug - it has to happen predictably (sorry)
+        . All the kernel tar files from a revision that worked to the
+          revision that doesn't
+
+You will then do:
+
+        . Rebuild a revision that you believe works, install, and verify that.
+        . Do a binary search over the kernels to figure out which one
+          introduced the bug.  I.e., suppose 1.3.28 didn't have the bug, but 
+          you know that 1.3.69 does.  Pick a kernel in the middle and build
+          that, like 1.3.50.  Build & test; if it works, pick the mid point
+          between .50 and .69, else the mid point between .28 and .50.
+        . You'll narrow it down to the kernel that introduced the bug.  You
+          can probably do better than this but it gets tricky.  
+
+        . Narrow it down to a subdirectory
+
+          - Copy kernel that works into "test".  Let's say that 3.62 works,
+            but 3.63 doesn't.  So you diff -r those two kernels and come
+            up with a list of directories that changed.  For each of those
+            directories:
+
+                Copy the non-working directory next to the working directory
+                as "dir.63".  
+                One directory at time, try moving the working directory to
+                "dir.62" and mv dir.63 dir"time, try 
+
+                        mv dir dir.62
+                        mv dir.63 dir
+                        find dir -name '*.[oa]' -print | xargs rm -f
+
+                And then rebuild and retest.  Assuming that all related
+                changes were contained in the sub directory, this should 
+                isolate the change to a directory.  
+
+                Problems: changes in header files may have occurred; I've
+                found in my case that they were self explanatory - you may 
+                or may not want to give up when that happens.
+
+        . Narrow it down to a file
+
+          - You can apply the same technique to each file in the directory,
+            hoping that the changes in that file are self contained.  
+            
+        . Narrow it down to a routine
+
+          - You can take the old file and the new file and manually create
+            a merged file that has
+
+                #ifdef VER62
+                routine()
+                {
+                        ...
+                }
+                #else
+                routine()
+                {
+                        ...
+                }
+                #endif
+
+            And then walk through that file, one routine at a time and
+            prefix it with
+
+                #define VER62
+                /* both routines here */
+                #undef VER62
+
+            Then recompile, retest, move the ifdefs until you find the one
+            that makes the difference.
+
+Finally, you take all the info that you have, kernel revisions, bug
+description, the extent to which you have narrowed it down, and pass 
+that off to whomever you believe is the maintainer of that section.
+A post to linux.dev.kernel isn't such a bad idea if you've done some
+work to narrow it down.
+
+If you get it down to a routine, you'll probably get a fix in 24 hours.
+
+My apologies to Linus and the other kernel hackers for describing this
+brute force approach, it's hardly what a kernel hacker would do.  However,
+it does work and it lets non-hackers help fix bugs.  And it is cool
+because Linux snapshots will let you do this - something that you can't
+do with vendor supplied releases.
+
diff --git a/Documentation/Changes b/Documentation/Changes
new file mode 100644
index 000000000000..caa6a5529b6b
--- /dev/null
+++ b/Documentation/Changes
@@ -0,0 +1,410 @@
+Intro
+=====
+
+This document is designed to provide a list of the minimum levels of
+software necessary to run the 2.6 kernels, as well as provide brief
+instructions regarding any other "Gotchas" users may encounter when
+trying life on the Bleeding Edge.  If upgrading from a pre-2.4.x
+kernel, please consult the Changes file included with 2.4.x kernels for
+additional information; most of that information will not be repeated
+here.  Basically, this document assumes that your system is already
+functional and running at least 2.4.x kernels.
+
+This document is originally based on my "Changes" file for 2.0.x kernels
+and therefore owes credit to the same people as that file (Jared Mauch,
+Axel Boldt, Alessandro Sigala, and countless other users all over the
+'net).
+
+The latest revision of this document, in various formats, can always
+be found at <http://cyberbuzz.gatech.edu/kaboom/linux/Changes-2.4/>.
+
+Feel free to translate this document.  If you do so, please send me a
+URL to your translation for inclusion in future revisions of this
+document.
+
+Smotrite file <http://oblom.rnc.ru/linux/kernel/Changes.ru>, yavlyaushisya
+russkim perevodom dannogo documenta.
+
+Visite <http://www2.adi.uam.es/~ender/tecnico/> para obtener la traducción
+al español de este documento en varios formatos.
+
+Eine deutsche Version dieser Datei finden Sie unter
+<http://www.stefan-winter.de/Changes-2.4.0.txt>.
+
+Last updated: October 29th, 2002
+
+Chris Ricker (kaboom@gatech.edu or chris.ricker@genetics.utah.edu).
+
+Current Minimal Requirements
+============================
+
+Upgrade to at *least* these software revisions before thinking you've
+encountered a bug!  If you're unsure what version you're currently
+running, the suggested command should tell you.
+
+Again, keep in mind that this list assumes you are already
+functionally running a Linux 2.4 kernel.  Also, not all tools are
+necessary on all systems; obviously, if you don't have any PCMCIA (PC
+Card) hardware, for example, you probably needn't concern yourself
+with pcmcia-cs.
+
+o  Gnu C                  2.95.3                  # gcc --version
+o  Gnu make               3.79.1                  # make --version
+o  binutils               2.12                    # ld -v
+o  util-linux             2.10o                   # fdformat --version
+o  module-init-tools      0.9.10                  # depmod -V
+o  e2fsprogs              1.29                    # tune2fs
+o  jfsutils               1.1.3                   # fsck.jfs -V
+o  reiserfsprogs          3.6.3                   # reiserfsck -V 2>&1|grep reiserfsprogs
+o  xfsprogs               2.6.0                   # xfs_db -V
+o  pcmcia-cs              3.1.21                  # cardmgr -V
+o  quota-tools            3.09                    # quota -V
+o  PPP                    2.4.0                   # pppd --version
+o  isdn4k-utils           3.1pre1                 # isdnctrl 2>&1|grep version
+o  nfs-utils              1.0.5                   # showmount --version
+o  procps                 3.2.0                   # ps --version
+o  oprofile               0.5.3                   # oprofiled --version
+
+Kernel compilation
+==================
+
+GCC
+---
+
+The gcc version requirements may vary depending on the type of CPU in your
+computer. The next paragraph applies to users of x86 CPUs, but not
+necessarily to users of other CPUs. Users of other CPUs should obtain
+information about their gcc version requirements from another source.
+
+The recommended compiler for the kernel is gcc 2.95.x (x >= 3), and it
+should be used when you need absolute stability. You may use gcc 3.0.x
+instead if you wish, although it may cause problems. Later versions of gcc 
+have not received much testing for Linux kernel compilation, and there are 
+almost certainly bugs (mainly, but not exclusively, in the kernel) that
+will need to be fixed in order to use these compilers. In any case, using
+pgcc instead of plain gcc is just asking for trouble.
+
+The Red Hat gcc 2.96 compiler subtree can also be used to build this tree.
+You should ensure you use gcc-2.96-74 or later. gcc-2.96-54 will not build
+the kernel correctly.
+
+In addition, please pay attention to compiler optimization.  Anything
+greater than -O2 may not be wise.  Similarly, if you choose to use gcc-2.95.x
+or derivatives, be sure not to use -fstrict-aliasing (which, depending on
+your version of gcc 2.95.x, may necessitate using -fno-strict-aliasing).
+
+Make
+----
+
+You will need Gnu make 3.79.1 or later to build the kernel.
+
+Binutils
+--------
+
+Linux on IA-32 has recently switched from using as86 to using gas for
+assembling the 16-bit boot code, removing the need for as86 to compile
+your kernel.  This change does, however, mean that you need a recent
+release of binutils.
+
+System utilities
+================
+
+Architectural changes
+---------------------
+
+DevFS has been obsoleted in favour of udev
+(http://www.kernel.org/pub/linux/utils/kernel/hotplug/)
+
+32-bit UID support is now in place.  Have fun!
+
+Linux documentation for functions is transitioning to inline
+documentation via specially-formatted comments near their
+definitions in the source.  These comments can be combined with the
+SGML templates in the Documentation/DocBook directory to make DocBook
+files, which can then be converted by DocBook stylesheets to PostScript,
+HTML, PDF files, and several other formats.  In order to convert from
+DocBook format to a format of your choice, you'll need to install Jade as
+well as the desired DocBook stylesheets.
+
+Util-linux
+----------
+
+New versions of util-linux provide *fdisk support for larger disks,
+support new options to mount, recognize more supported partition
+types, have a fdformat which works with 2.4 kernels, and similar goodies.
+You'll probably want to upgrade.
+
+Ksymoops
+--------
+
+If the unthinkable happens and your kernel oopses, you'll need a 2.4
+version of ksymoops to decode the report; see REPORTING-BUGS in the
+root of the Linux source for more information.
+
+Module-Init-Tools
+-----------------
+
+A new module loader is now in the kernel that requires module-init-tools
+to use.  It is backward compatible with the 2.4.x series kernels.
+
+Mkinitrd
+--------
+
+These changes to the /lib/modules file tree layout also require that
+mkinitrd be upgraded.
+
+E2fsprogs
+---------
+
+The latest version of e2fsprogs fixes several bugs in fsck and
+debugfs.  Obviously, it's a good idea to upgrade.
+
+JFSutils
+--------
+
+The jfsutils package contains the utilities for the file system.
+The following utilities are available:
+o fsck.jfs - initiate replay of the transaction log, and check
+  and repair a JFS formatted partition.
+o mkfs.jfs - create a JFS formatted partition.
+o other file system utilities are also available in this package.
+
+Reiserfsprogs
+-------------
+
+The reiserfsprogs package should be used for reiserfs-3.6.x
+(Linux kernels 2.4.x). It is a combined package and contains working
+versions of mkreiserfs, resize_reiserfs, debugreiserfs and
+reiserfsck. These utils work on both i386 and alpha platforms.
+
+Xfsprogs
+--------
+
+The latest version of xfsprogs contains mkfs.xfs, xfs_db, and the
+xfs_repair utilities, among others, for the XFS filesystem.  It is
+architecture independent and any version from 2.0.0 onward should
+work correctly with this version of the XFS kernel code (2.6.0 or
+later is recommended, due to some significant improvements).
+
+
+Pcmcia-cs
+---------
+
+PCMCIA (PC Card) support is now partially implemented in the main
+kernel source.  Pay attention when you recompile your kernel ;-).
+Also, be sure to upgrade to the latest pcmcia-cs release.
+
+Quota-tools
+-----------
+
+Support for 32 bit uid's and gid's is required if you want to use
+the newer version 2 quota format.  Quota-tools version 3.07 and
+newer has this support.  Use the recommended version or newer
+from the table above.
+
+Intel IA32 microcode
+--------------------
+
+A driver has been added to allow updating of Intel IA32 microcode,
+accessible as both a devfs regular file and as a normal (misc)
+character device.  If you are not using devfs you may need to:
+
+mkdir /dev/cpu
+mknod /dev/cpu/microcode c 10 184
+chmod 0644 /dev/cpu/microcode
+
+as root before you can use this.  You'll probably also want to
+get the user-space microcode_ctl utility to use with this.
+
+Powertweak
+----------
+
+If you are running v0.1.17 or earlier, you should upgrade to
+version v0.99.0 or higher. Running old versions may cause problems
+with programs using shared memory.
+
+udev
+----
+udev is a userspace application for populating /dev dynamically with
+only entries for devices actually present. udev replaces devfs.
+
+Networking
+==========
+
+General changes
+---------------
+
+If you have advanced network configuration needs, you should probably
+consider using the network tools from ip-route2.
+
+Packet Filter / NAT
+-------------------
+The packet filtering and NAT code uses the same tools like the previous 2.4.x
+kernel series (iptables).  It still includes backwards-compatibility modules
+for 2.2.x-style ipchains and 2.0.x-style ipfwadm.
+
+PPP
+---
+
+The PPP driver has been restructured to support multilink and to
+enable it to operate over diverse media layers.  If you use PPP,
+upgrade pppd to at least 2.4.0.
+
+If you are not using devfs, you must have the device file /dev/ppp
+which can be made by:
+
+mknod /dev/ppp c 108 0
+
+as root.
+
+If you use devfsd and build ppp support as modules, you will need
+the following in your /etc/devfsd.conf file:
+
+LOOKUP	PPP	MODLOAD
+
+Isdn4k-utils
+------------
+
+Due to changes in the length of the phone number field, isdn4k-utils
+needs to be recompiled or (preferably) upgraded.
+
+NFS-utils
+---------
+
+In 2.4 and earlier kernels, the nfs server needed to know about any
+client that expected to be able to access files via NFS.  This
+information would be given to the kernel by "mountd" when the client
+mounted the filesystem, or by "exportfs" at system startup.  exportfs
+would take information about active clients from /var/lib/nfs/rmtab.
+
+This approach is quite fragile as it depends on rmtab being correct
+which is not always easy, particularly when trying to implement
+fail-over.  Even when the system is working well, rmtab suffers from
+getting lots of old entries that never get removed.
+
+With 2.6 we have the option of having the kernel tell mountd when it
+gets a request from an unknown host, and mountd can give appropriate
+export information to the kernel.  This removes the dependency on
+rmtab and means that the kernel only needs to know about currently
+active clients.
+
+To enable this new functionality, you need to:
+
+  mount -t nfsd nfsd /proc/fs/nfs
+
+before running exportfs or mountd.  It is recommended that all NFS
+services be protected from the internet-at-large by a firewall where
+that is possible.
+
+Getting updated software
+========================
+
+Kernel compilation
+******************
+
+gcc 2.95.3
+----------
+o  <ftp://ftp.gnu.org/gnu/gcc/gcc-2.95.3.tar.gz>
+
+Make
+----
+o  <ftp://ftp.gnu.org/gnu/make/>
+
+Binutils
+--------
+o  <ftp://ftp.kernel.org/pub/linux/devel/binutils/>
+
+System utilities
+****************
+
+Util-linux
+----------
+o  <ftp://ftp.kernel.org/pub/linux/utils/util-linux/>
+
+Ksymoops
+--------
+o  <ftp://ftp.kernel.org/pub/linux/utils/kernel/ksymoops/v2.4/>
+
+Module-Init-Tools
+-----------------
+o  <ftp://ftp.kernel.org/pub/linux/kernel/people/rusty/modules/>
+
+Mkinitrd
+--------
+o  <ftp://rawhide.redhat.com/pub/rawhide/SRPMS/SRPMS/>
+
+E2fsprogs
+---------
+o  <http://prdownloads.sourceforge.net/e2fsprogs/e2fsprogs-1.29.tar.gz>
+
+JFSutils
+--------
+o  <http://jfs.sourceforge.net/>
+
+Reiserfsprogs
+-------------
+o  <http://www.namesys.com/pub/reiserfsprogs/reiserfsprogs-3.6.3.tar.gz>
+
+Xfsprogs
+--------
+o  <ftp://oss.sgi.com/projects/xfs/download/>
+
+Pcmcia-cs
+---------
+o  <ftp://pcmcia-cs.sourceforge.net/pub/pcmcia-cs/pcmcia-cs-3.1.21.tar.gz>
+
+Quota-tools
+----------
+o  <http://sourceforge.net/projects/linuxquota/>
+
+Jade
+----
+o  <ftp://ftp.jclark.com/pub/jade/jade-1.2.1.tar.gz>
+
+DocBook Stylesheets
+-------------------
+o  <http://nwalsh.com/docbook/dsssl/>
+
+Intel P6 microcode
+------------------
+o  <http://www.urbanmyth.org/microcode/>
+
+Powertweak
+----------
+o  <http://powertweak.sourceforge.net/>
+
+udev
+----
+o <http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html>
+
+Networking
+**********
+
+PPP
+---
+o  <ftp://ftp.samba.org/pub/ppp/ppp-2.4.0.tar.gz>
+
+Isdn4k-utils
+------------
+o  <ftp://ftp.isdn4linux.de/pub/isdn4linux/utils/isdn4k-utils.v3.1pre1.tar.gz>
+
+NFS-utils
+---------
+o  <http://sourceforge.net/project/showfiles.php?group_id=14>
+
+Iptables
+--------
+o  <http://www.iptables.org/downloads.html>
+
+Ip-route2
+---------
+o  <ftp://ftp.tux.org/pub/net/ip-routing/iproute2-2.2.4-now-ss991023.tar.gz>
+
+OProfile
+--------
+o  <http://oprofile.sf.net/download/>
+
+NFS-Utils
+---------
+o  <http://nfs.sourceforge.net/>
+
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
new file mode 100644
index 000000000000..f25b3953f513
--- /dev/null
+++ b/Documentation/CodingStyle
@@ -0,0 +1,431 @@
+
+		Linux kernel coding style
+
+This is a short document describing the preferred coding style for the
+linux kernel.  Coding style is very personal, and I won't _force_ my
+views on anybody, but this is what goes for anything that I have to be
+able to maintain, and I'd prefer it for most other things too.  Please
+at least consider the points made here.
+
+First off, I'd suggest printing out a copy of the GNU coding standards,
+and NOT read it.  Burn them, it's a great symbolic gesture.
+
+Anyway, here goes:
+
+
+	 	Chapter 1: Indentation
+
+Tabs are 8 characters, and thus indentations are also 8 characters.
+There are heretic movements that try to make indentations 4 (or even 2!)
+characters deep, and that is akin to trying to define the value of PI to
+be 3.
+
+Rationale: The whole idea behind indentation is to clearly define where
+a block of control starts and ends.  Especially when you've been looking
+at your screen for 20 straight hours, you'll find it a lot easier to see
+how the indentation works if you have large indentations.
+
+Now, some people will claim that having 8-character indentations makes
+the code move too far to the right, and makes it hard to read on a
+80-character terminal screen.  The answer to that is that if you need
+more than 3 levels of indentation, you're screwed anyway, and should fix
+your program.
+
+In short, 8-char indents make things easier to read, and have the added
+benefit of warning you when you're nesting your functions too deep.
+Heed that warning.
+
+Don't put multiple statements on a single line unless you have
+something to hide:
+
+	if (condition) do_this;
+	  do_something_everytime;
+
+Outside of comments, documentation and except in Kconfig, spaces are never
+used for indentation, and the above example is deliberately broken.
+
+Get a decent editor and don't leave whitespace at the end of lines.
+
+
+		Chapter 2: Breaking long lines and strings
+
+Coding style is all about readability and maintainability using commonly
+available tools.
+
+The limit on the length of lines is 80 columns and this is a hard limit.
+
+Statements longer than 80 columns will be broken into sensible chunks.
+Descendants are always substantially shorter than the parent and are placed
+substantially to the right. The same applies to function headers with a long
+argument list. Long strings are as well broken into shorter strings.
+
+void fun(int a, int b, int c)
+{
+	if (condition)
+		printk(KERN_WARNING "Warning this is a long printk with "
+						"3 parameters a: %u b: %u "
+						"c: %u \n", a, b, c);
+	else
+		next_statement;
+}
+
+		Chapter 3: Placing Braces
+
+The other issue that always comes up in C styling is the placement of
+braces.  Unlike the indent size, there are few technical reasons to
+choose one placement strategy over the other, but the preferred way, as
+shown to us by the prophets Kernighan and Ritchie, is to put the opening
+brace last on the line, and put the closing brace first, thusly:
+
+	if (x is true) {
+		we do y
+	}
+
+However, there is one special case, namely functions: they have the
+opening brace at the beginning of the next line, thus:
+
+	int function(int x)
+	{
+		body of function
+	}
+
+Heretic people all over the world have claimed that this inconsistency
+is ...  well ...  inconsistent, but all right-thinking people know that
+(a) K&R are _right_ and (b) K&R are right.  Besides, functions are
+special anyway (you can't nest them in C).
+
+Note that the closing brace is empty on a line of its own, _except_ in
+the cases where it is followed by a continuation of the same statement,
+ie a "while" in a do-statement or an "else" in an if-statement, like
+this:
+
+	do {
+		body of do-loop
+	} while (condition);
+
+and
+
+	if (x == y) {
+		..
+	} else if (x > y) {
+		...
+	} else {
+		....
+	}
+
+Rationale: K&R.
+
+Also, note that this brace-placement also minimizes the number of empty
+(or almost empty) lines, without any loss of readability.  Thus, as the
+supply of new-lines on your screen is not a renewable resource (think
+25-line terminal screens here), you have more empty lines to put
+comments on.
+
+
+		Chapter 4: Naming
+
+C is a Spartan language, and so should your naming be.  Unlike Modula-2
+and Pascal programmers, C programmers do not use cute names like
+ThisVariableIsATemporaryCounter.  A C programmer would call that
+variable "tmp", which is much easier to write, and not the least more
+difficult to understand.
+
+HOWEVER, while mixed-case names are frowned upon, descriptive names for
+global variables are a must.  To call a global function "foo" is a
+shooting offense.
+
+GLOBAL variables (to be used only if you _really_ need them) need to
+have descriptive names, as do global functions.  If you have a function
+that counts the number of active users, you should call that
+"count_active_users()" or similar, you should _not_ call it "cntusr()".
+
+Encoding the type of a function into the name (so-called Hungarian
+notation) is brain damaged - the compiler knows the types anyway and can
+check those, and it only confuses the programmer.  No wonder MicroSoft
+makes buggy programs.
+
+LOCAL variable names should be short, and to the point.  If you have
+some random integer loop counter, it should probably be called "i".
+Calling it "loop_counter" is non-productive, if there is no chance of it
+being mis-understood.  Similarly, "tmp" can be just about any type of
+variable that is used to hold a temporary value.
+
+If you are afraid to mix up your local variable names, you have another
+problem, which is called the function-growth-hormone-imbalance syndrome.
+See next chapter.
+
+
+		Chapter 5: Functions
+
+Functions should be short and sweet, and do just one thing.  They should
+fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,
+as we all know), and do one thing and do that well.
+
+The maximum length of a function is inversely proportional to the
+complexity and indentation level of that function.  So, if you have a
+conceptually simple function that is just one long (but simple)
+case-statement, where you have to do lots of small things for a lot of
+different cases, it's OK to have a longer function.
+
+However, if you have a complex function, and you suspect that a
+less-than-gifted first-year high-school student might not even
+understand what the function is all about, you should adhere to the
+maximum limits all the more closely.  Use helper functions with
+descriptive names (you can ask the compiler to in-line them if you think
+it's performance-critical, and it will probably do a better job of it
+than you would have done).
+
+Another measure of the function is the number of local variables.  They
+shouldn't exceed 5-10, or you're doing something wrong.  Re-think the
+function, and split it into smaller pieces.  A human brain can
+generally easily keep track of about 7 different things, anything more
+and it gets confused.  You know you're brilliant, but maybe you'd like
+to understand what you did 2 weeks from now.
+
+
+		Chapter 6: Centralized exiting of functions
+
+Albeit deprecated by some people, the equivalent of the goto statement is
+used frequently by compilers in form of the unconditional jump instruction.
+
+The goto statement comes in handy when a function exits from multiple
+locations and some common work such as cleanup has to be done.
+
+The rationale is:
+
+- unconditional statements are easier to understand and follow
+- nesting is reduced
+- errors by not updating individual exit points when making
+    modifications are prevented
+- saves the compiler work to optimize redundant code away ;)
+
+int fun(int )
+{
+	int result = 0;
+	char *buffer = kmalloc(SIZE);
+
+	if (buffer == NULL)
+		return -ENOMEM;
+
+	if (condition1) {
+		while (loop1) {
+			...
+		}
+		result = 1;
+		goto out;
+	}
+	...
+out:
+	kfree(buffer);
+	return result;
+}
+
+		Chapter 7: Commenting
+
+Comments are good, but there is also a danger of over-commenting.  NEVER
+try to explain HOW your code works in a comment: it's much better to
+write the code so that the _working_ is obvious, and it's a waste of
+time to explain badly written code.
+
+Generally, you want your comments to tell WHAT your code does, not HOW.
+Also, try to avoid putting comments inside a function body: if the
+function is so complex that you need to separately comment parts of it,
+you should probably go back to chapter 5 for a while.  You can make
+small comments to note or warn about something particularly clever (or
+ugly), but try to avoid excess.  Instead, put the comments at the head
+of the function, telling people what it does, and possibly WHY it does
+it.
+
+
+		Chapter 8: You've made a mess of it
+
+That's OK, we all do.  You've probably been told by your long-time Unix
+user helper that "GNU emacs" automatically formats the C sources for
+you, and you've noticed that yes, it does do that, but the defaults it
+uses are less than desirable (in fact, they are worse than random
+typing - an infinite number of monkeys typing into GNU emacs would never
+make a good program).
+
+So, you can either get rid of GNU emacs, or change it to use saner
+values.  To do the latter, you can stick the following in your .emacs file:
+
+(defun linux-c-mode ()
+  "C mode with adjusted defaults for use with the Linux kernel."
+  (interactive)
+  (c-mode)
+  (c-set-style "K&R")
+  (setq tab-width 8)
+  (setq indent-tabs-mode t)
+  (setq c-basic-offset 8))
+
+This will define the M-x linux-c-mode command.  When hacking on a
+module, if you put the string -*- linux-c -*- somewhere on the first
+two lines, this mode will be automatically invoked. Also, you may want
+to add
+
+(setq auto-mode-alist (cons '("/usr/src/linux.*/.*\\.[ch]$" . linux-c-mode)
+			auto-mode-alist))
+
+to your .emacs file if you want to have linux-c-mode switched on
+automagically when you edit source files under /usr/src/linux.
+
+But even if you fail in getting emacs to do sane formatting, not
+everything is lost: use "indent".
+
+Now, again, GNU indent has the same brain-dead settings that GNU emacs
+has, which is why you need to give it a few command line options.
+However, that's not too bad, because even the makers of GNU indent
+recognize the authority of K&R (the GNU people aren't evil, they are
+just severely misguided in this matter), so you just give indent the
+options "-kr -i8" (stands for "K&R, 8 character indents"), or use
+"scripts/Lindent", which indents in the latest style.
+
+"indent" has a lot of options, and especially when it comes to comment
+re-formatting you may want to take a look at the man page.  But
+remember: "indent" is not a fix for bad programming.
+
+
+		Chapter 9: Configuration-files
+
+For configuration options (arch/xxx/Kconfig, and all the Kconfig files),
+somewhat different indentation is used.
+
+Help text is indented with 2 spaces.
+
+if CONFIG_EXPERIMENTAL
+	tristate CONFIG_BOOM
+	default n
+	help
+	  Apply nitroglycerine inside the keyboard (DANGEROUS)
+	bool CONFIG_CHEER
+	depends on CONFIG_BOOM
+	default y
+	help
+	  Output nice messages when you explode
+endif
+
+Generally, CONFIG_EXPERIMENTAL should surround all options not considered
+stable. All options that are known to trash data (experimental write-
+support for file-systems, for instance) should be denoted (DANGEROUS), other
+experimental options should be denoted (EXPERIMENTAL).
+
+
+		Chapter 10: Data structures
+
+Data structures that have visibility outside the single-threaded
+environment they are created and destroyed in should always have
+reference counts.  In the kernel, garbage collection doesn't exist (and
+outside the kernel garbage collection is slow and inefficient), which
+means that you absolutely _have_ to reference count all your uses.
+
+Reference counting means that you can avoid locking, and allows multiple
+users to have access to the data structure in parallel - and not having
+to worry about the structure suddenly going away from under them just
+because they slept or did something else for a while.
+
+Note that locking is _not_ a replacement for reference counting.
+Locking is used to keep data structures coherent, while reference
+counting is a memory management technique.  Usually both are needed, and
+they are not to be confused with each other.
+
+Many data structures can indeed have two levels of reference counting,
+when there are users of different "classes".  The subclass count counts
+the number of subclass users, and decrements the global count just once
+when the subclass count goes to zero.
+
+Examples of this kind of "multi-level-reference-counting" can be found in
+memory management ("struct mm_struct": mm_users and mm_count), and in
+filesystem code ("struct super_block": s_count and s_active).
+
+Remember: if another thread can find your data structure, and you don't
+have a reference count on it, you almost certainly have a bug.
+
+
+		Chapter 11: Macros, Enums, Inline functions and RTL
+
+Names of macros defining constants and labels in enums are capitalized.
+
+#define CONSTANT 0x12345
+
+Enums are preferred when defining several related constants.
+
+CAPITALIZED macro names are appreciated but macros resembling functions
+may be named in lower case.
+
+Generally, inline functions are preferable to macros resembling functions.
+
+Macros with multiple statements should be enclosed in a do - while block:
+
+#define macrofun(a, b, c) 			\
+	do {					\
+		if (a == 5)			\
+			do_this(b, c);		\
+	} while (0)
+
+Things to avoid when using macros:
+
+1) macros that affect control flow:
+
+#define FOO(x)					\
+	do {					\
+		if (blah(x) < 0)		\
+			return -EBUGGERED;	\
+	} while(0)
+
+is a _very_ bad idea.  It looks like a function call but exits the "calling"
+function; don't break the internal parsers of those who will read the code.
+
+2) macros that depend on having a local variable with a magic name:
+
+#define FOO(val) bar(index, val)
+
+might look like a good thing, but it's confusing as hell when one reads the
+code and it's prone to breakage from seemingly innocent changes.
+
+3) macros with arguments that are used as l-values: FOO(x) = y; will
+bite you if somebody e.g. turns FOO into an inline function.
+
+4) forgetting about precedence: macros defining constants using expressions
+must enclose the expression in parentheses. Beware of similar issues with
+macros using parameters.
+
+#define CONSTANT 0x4000
+#define CONSTEXP (CONSTANT | 3)
+
+The cpp manual deals with macros exhaustively. The gcc internals manual also
+covers RTL which is used frequently with assembly language in the kernel.
+
+
+		Chapter 12: Printing kernel messages
+
+Kernel developers like to be seen as literate. Do mind the spelling
+of kernel messages to make a good impression. Do not use crippled
+words like "dont" and use "do not" or "don't" instead.
+
+Kernel messages do not have to be terminated with a period.
+
+Printing numbers in parentheses (%d) adds no value and should be avoided.
+
+
+		Chapter 13: References
+
+The C Programming Language, Second Edition
+by Brian W. Kernighan and Dennis M. Ritchie.
+Prentice Hall, Inc., 1988.
+ISBN 0-13-110362-8 (paperback), 0-13-110370-9 (hardback).
+URL: http://cm.bell-labs.com/cm/cs/cbook/
+
+The Practice of Programming
+by Brian W. Kernighan and Rob Pike.
+Addison-Wesley, Inc., 1999.
+ISBN 0-201-61586-X.
+URL: http://cm.bell-labs.com/cm/cs/tpop/
+
+GNU manuals - where in compliance with K&R and this text - for cpp, gcc,
+gcc internals and indent, all available from http://www.gnu.org
+
+WG14 is the international standardization working group for the programming
+language C, URL: http://std.dkuug.dk/JTC1/SC22/WG14/
+
+--
+Last updated on 16 February 2004 by a community effort on LKML.
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
new file mode 100644
index 000000000000..6ee3cd6134df
--- /dev/null
+++ b/Documentation/DMA-API.txt
@@ -0,0 +1,526 @@
+               Dynamic DMA mapping using the generic device
+               ============================================
+
+        James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
+
+This document describes the DMA API.  For a more gentle introduction
+phrased in terms of the pci_ equivalents (and actual examples) see
+DMA-mapping.txt
+
+This API is split into two pieces.  Part I describes the API and the
+corresponding pci_ API.  Part II describes the extensions to the API
+for supporting non-consistent memory machines.  Unless you know that
+your driver absolutely has to support non-consistent platforms (this
+is usually only legacy platforms) you should only use the API
+described in part I.
+
+Part I - pci_ and dma_ Equivalent API 
+-------------------------------------
+
+To get the pci_ API, you must #include <linux/pci.h>
+To get the dma_ API, you must #include <linux/dma-mapping.h>
+
+
+Part Ia - Using large dma-coherent buffers
+------------------------------------------
+
+void *
+dma_alloc_coherent(struct device *dev, size_t size,
+			     dma_addr_t *dma_handle, int flag)
+void *
+pci_alloc_consistent(struct pci_dev *dev, size_t size,
+			     dma_addr_t *dma_handle)
+
+Consistent memory is memory for which a write by either the device or
+the processor can immediately be read by the processor or device
+without having to worry about caching effects.
+
+This routine allocates a region of <size> bytes of consistent memory.
+it also returns a <dma_handle> which may be cast to an unsigned
+integer the same width as the bus and used as the physical address
+base of the region.
+
+Returns: a pointer to the allocated region (in the processor's virtual
+address space) or NULL if the allocation failed.
+
+Note: consistent memory can be expensive on some platforms, and the
+minimum allocation length may be as big as a page, so you should
+consolidate your requests for consistent memory as much as possible.
+The simplest way to do that is to use the dma_pool calls (see below).
+
+The flag parameter (dma_alloc_coherent only) allows the caller to
+specify the GFP_ flags (see kmalloc) for the allocation (the
+implementation may chose to ignore flags that affect the location of
+the returned memory, like GFP_DMA).  For pci_alloc_consistent, you
+must assume GFP_ATOMIC behaviour.
+
+void
+dma_free_coherent(struct device *dev, size_t size, void *cpu_addr
+			   dma_addr_t dma_handle)
+void
+pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr
+			   dma_addr_t dma_handle)
+
+Free the region of consistent memory you previously allocated.  dev,
+size and dma_handle must all be the same as those passed into the
+consistent allocate.  cpu_addr must be the virtual address returned by
+the consistent allocate
+
+
+Part Ib - Using small dma-coherent buffers
+------------------------------------------
+
+To get this part of the dma_ API, you must #include <linux/dmapool.h>
+
+Many drivers need lots of small dma-coherent memory regions for DMA
+descriptors or I/O buffers.  Rather than allocating in units of a page
+or more using dma_alloc_coherent(), you can use DMA pools.  These work
+much like a kmem_cache_t, except that they use the dma-coherent allocator
+not __get_free_pages().  Also, they understand common hardware constraints
+for alignment, like queue heads needing to be aligned on N byte boundaries.
+
+
+	struct dma_pool *
+	dma_pool_create(const char *name, struct device *dev,
+			size_t size, size_t align, size_t alloc);
+
+	struct pci_pool *
+	pci_pool_create(const char *name, struct pci_device *dev,
+			size_t size, size_t align, size_t alloc);
+
+The pool create() routines initialize a pool of dma-coherent buffers
+for use with a given device.  It must be called in a context which
+can sleep.
+
+The "name" is for diagnostics (like a kmem_cache_t name); dev and size
+are like what you'd pass to dma_alloc_coherent().  The device's hardware
+alignment requirement for this type of data is "align" (which is expressed
+in bytes, and must be a power of two).  If your device has no boundary
+crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
+from this pool must not cross 4KByte boundaries.
+
+
+	void *dma_pool_alloc(struct dma_pool *pool, int gfp_flags,
+			dma_addr_t *dma_handle);
+
+	void *pci_pool_alloc(struct pci_pool *pool, int gfp_flags,
+			dma_addr_t *dma_handle);
+
+This allocates memory from the pool; the returned memory will meet the size
+and alignment requirements specified at creation time.  Pass GFP_ATOMIC to
+prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks)
+pass GFP_KERNEL to allow blocking.  Like dma_alloc_coherent(), this returns
+two values:  an address usable by the cpu, and the dma address usable by the
+pool's device.
+
+
+	void dma_pool_free(struct dma_pool *pool, void *vaddr,
+			dma_addr_t addr);
+
+	void pci_pool_free(struct pci_pool *pool, void *vaddr,
+			dma_addr_t addr);
+
+This puts memory back into the pool.  The pool is what was passed to
+the the pool allocation routine; the cpu and dma addresses are what
+were returned when that routine allocated the memory being freed.
+
+
+	void dma_pool_destroy(struct dma_pool *pool);
+
+	void pci_pool_destroy(struct pci_pool *pool);
+
+The pool destroy() routines free the resources of the pool.  They must be
+called in a context which can sleep.  Make sure you've freed all allocated
+memory back to the pool before you destroy it.
+
+
+Part Ic - DMA addressing limitations
+------------------------------------
+
+int
+dma_supported(struct device *dev, u64 mask)
+int
+pci_dma_supported(struct device *dev, u64 mask)
+
+Checks to see if the device can support DMA to the memory described by
+mask.
+
+Returns: 1 if it can and 0 if it can't.
+
+Notes: This routine merely tests to see if the mask is possible.  It
+won't change the current mask settings.  It is more intended as an
+internal API for use by the platform than an external API for use by
+driver writers.
+
+int
+dma_set_mask(struct device *dev, u64 mask)
+int
+pci_set_dma_mask(struct pci_device *dev, u64 mask)
+
+Checks to see if the mask is possible and updates the device
+parameters if it is.
+
+Returns: 0 if successful and a negative error if not.
+
+u64
+dma_get_required_mask(struct device *dev)
+
+After setting the mask with dma_set_mask(), this API returns the
+actual mask (within that already set) that the platform actually
+requires to operate efficiently.  Usually this means the returned mask
+is the minimum required to cover all of memory.  Examining the
+required mask gives drivers with variable descriptor sizes the
+opportunity to use smaller descriptors as necessary.
+
+Requesting the required mask does not alter the current mask.  If you
+wish to take advantage of it, you should issue another dma_set_mask()
+call to lower the mask again.
+
+
+Part Id - Streaming DMA mappings
+--------------------------------
+
+dma_addr_t
+dma_map_single(struct device *dev, void *cpu_addr, size_t size,
+		      enum dma_data_direction direction)
+dma_addr_t
+pci_map_single(struct device *dev, void *cpu_addr, size_t size,
+		      int direction)
+
+Maps a piece of processor virtual memory so it can be accessed by the
+device and returns the physical handle of the memory.
+
+The direction for both api's may be converted freely by casting.
+However the dma_ API uses a strongly typed enumerator for its
+direction:
+
+DMA_NONE		= PCI_DMA_NONE		no direction (used for
+						debugging)
+DMA_TO_DEVICE		= PCI_DMA_TODEVICE	data is going from the
+						memory to the device
+DMA_FROM_DEVICE		= PCI_DMA_FROMDEVICE	data is coming from
+						the device to the
+						memory
+DMA_BIDIRECTIONAL	= PCI_DMA_BIDIRECTIONAL	direction isn't known
+
+Notes:  Not all memory regions in a machine can be mapped by this
+API.  Further, regions that appear to be physically contiguous in
+kernel virtual space may not be contiguous as physical memory.  Since
+this API does not provide any scatter/gather capability, it will fail
+if the user tries to map a non physically contiguous piece of memory.
+For this reason, it is recommended that memory mapped by this API be
+obtained only from sources which guarantee to be physically contiguous
+(like kmalloc).
+
+Further, the physical address of the memory must be within the
+dma_mask of the device (the dma_mask represents a bit mask of the
+addressable region for the device.  i.e. if the physical address of
+the memory anded with the dma_mask is still equal to the physical
+address, then the device can perform DMA to the memory).  In order to
+ensure that the memory allocated by kmalloc is within the dma_mask,
+the driver may specify various platform dependent flags to restrict
+the physical memory range of the allocation (e.g. on x86, GFP_DMA
+guarantees to be within the first 16Mb of available physical memory,
+as required by ISA devices).
+
+Note also that the above constraints on physical contiguity and
+dma_mask may not apply if the platform has an IOMMU (a device which
+supplies a physical to virtual mapping between the I/O memory bus and
+the device).  However, to be portable, device driver writers may *not*
+assume that such an IOMMU exists.
+
+Warnings:  Memory coherency operates at a granularity called the cache
+line width.  In order for memory mapped by this API to operate
+correctly, the mapped region must begin exactly on a cache line
+boundary and end exactly on one (to prevent two separately mapped
+regions from sharing a single cache line).  Since the cache line size
+may not be known at compile time, the API will not enforce this
+requirement.  Therefore, it is recommended that driver writers who
+don't take special care to determine the cache line size at run time
+only map virtual regions that begin and end on page boundaries (which
+are guaranteed also to be cache line boundaries).
+
+DMA_TO_DEVICE synchronisation must be done after the last modification
+of the memory region by the software and before it is handed off to
+the driver.  Once this primitive is used.  Memory covered by this
+primitive should be treated as read only by the device.  If the device
+may write to it at any point, it should be DMA_BIDIRECTIONAL (see
+below).
+
+DMA_FROM_DEVICE synchronisation must be done before the driver
+accesses data that may be changed by the device.  This memory should
+be treated as read only by the driver.  If the driver needs to write
+to it at any point, it should be DMA_BIDIRECTIONAL (see below).
+
+DMA_BIDIRECTIONAL requires special handling: it means that the driver
+isn't sure if the memory was modified before being handed off to the
+device and also isn't sure if the device will also modify it.  Thus,
+you must always sync bidirectional memory twice: once before the
+memory is handed off to the device (to make sure all memory changes
+are flushed from the processor) and once before the data may be
+accessed after being used by the device (to make sure any processor
+cache lines are updated with data that the device may have changed.
+
+void
+dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
+		 enum dma_data_direction direction)
+void
+pci_unmap_single(struct pci_dev *hwdev, dma_addr_t dma_addr,
+		 size_t size, int direction)
+
+Unmaps the region previously mapped.  All the parameters passed in
+must be identical to those passed in (and returned) by the mapping
+API.
+
+dma_addr_t
+dma_map_page(struct device *dev, struct page *page,
+		    unsigned long offset, size_t size,
+		    enum dma_data_direction direction)
+dma_addr_t
+pci_map_page(struct pci_dev *hwdev, struct page *page,
+		    unsigned long offset, size_t size, int direction)
+void
+dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
+	       enum dma_data_direction direction)
+void
+pci_unmap_page(struct pci_dev *hwdev, dma_addr_t dma_address,
+	       size_t size, int direction)
+
+API for mapping and unmapping for pages.  All the notes and warnings
+for the other mapping APIs apply here.  Also, although the <offset>
+and <size> parameters are provided to do partial page mapping, it is
+recommended that you never use these unless you really know what the
+cache width is.
+
+int
+dma_mapping_error(dma_addr_t dma_addr)
+
+int
+pci_dma_mapping_error(dma_addr_t dma_addr)
+
+In some circumstances dma_map_single and dma_map_page will fail to create
+a mapping. A driver can check for these errors by testing the returned
+dma address with dma_mapping_error(). A non zero return value means the mapping
+could not be created and the driver should take appropriate action (eg
+reduce current DMA mapping usage or delay and try again later).
+
+int
+dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+	   enum dma_data_direction direction)
+int
+pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
+	   int nents, int direction)
+
+Maps a scatter gather list from the block layer.
+
+Returns: the number of physical segments mapped (this may be shorted
+than <nents> passed in if the block layer determines that some
+elements of the scatter/gather list are physically adjacent and thus
+may be mapped with a single entry).
+
+Please note that the sg cannot be mapped again if it has been mapped once.
+The mapping process is allowed to destroy information in the sg.
+
+As with the other mapping interfaces, dma_map_sg can fail. When it
+does, 0 is returned and a driver must take appropriate action. It is
+critical that the driver do something, in the case of a block driver
+aborting the request or even oopsing is better than doing nothing and
+corrupting the filesystem.
+
+void
+dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nhwentries,
+	     enum dma_data_direction direction)
+void
+pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
+	     int nents, int direction)
+
+unmap the previously mapped scatter/gather list.  All the parameters
+must be the same as those and passed in to the scatter/gather mapping
+API.
+
+Note: <nents> must be the number you passed in, *not* the number of
+physical entries returned.
+
+void
+dma_sync_single(struct device *dev, dma_addr_t dma_handle, size_t size,
+		enum dma_data_direction direction)
+void
+pci_dma_sync_single(struct pci_dev *hwdev, dma_addr_t dma_handle,
+			   size_t size, int direction)
+void
+dma_sync_sg(struct device *dev, struct scatterlist *sg, int nelems,
+			  enum dma_data_direction direction)
+void
+pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg,
+		       int nelems, int direction)
+
+synchronise a single contiguous or scatter/gather mapping.  All the
+parameters must be the same as those passed into the single mapping
+API.
+
+Notes:  You must do this:
+
+- Before reading values that have been written by DMA from the device
+  (use the DMA_FROM_DEVICE direction)
+- After writing values that will be written to the device using DMA
+  (use the DMA_TO_DEVICE) direction
+- before *and* after handing memory to the device if the memory is
+  DMA_BIDIRECTIONAL
+
+See also dma_map_single().
+
+
+Part II - Advanced dma_ usage
+-----------------------------
+
+Warning: These pieces of the DMA API have no PCI equivalent.  They
+should also not be used in the majority of cases, since they cater for
+unlikely corner cases that don't belong in usual drivers.
+
+If you don't understand how cache line coherency works between a
+processor and an I/O device, you should not be using this part of the
+API at all.
+
+void *
+dma_alloc_noncoherent(struct device *dev, size_t size,
+			       dma_addr_t *dma_handle, int flag)
+
+Identical to dma_alloc_coherent() except that the platform will
+choose to return either consistent or non-consistent memory as it sees
+fit.  By using this API, you are guaranteeing to the platform that you
+have all the correct and necessary sync points for this memory in the
+driver should it choose to return non-consistent memory.
+
+Note: where the platform can return consistent memory, it will
+guarantee that the sync points become nops.
+
+Warning:  Handling non-consistent memory is a real pain.  You should
+only ever use this API if you positively know your driver will be
+required to work on one of the rare (usually non-PCI) architectures
+that simply cannot make consistent memory.
+
+void
+dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
+			      dma_addr_t dma_handle)
+
+free memory allocated by the nonconsistent API.  All parameters must
+be identical to those passed in (and returned by
+dma_alloc_noncoherent()).
+
+int
+dma_is_consistent(dma_addr_t dma_handle)
+
+returns true if the memory pointed to by the dma_handle is actually
+consistent.
+
+int
+dma_get_cache_alignment(void)
+
+returns the processor cache alignment.  This is the absolute minimum
+alignment *and* width that you must observe when either mapping
+memory or doing partial flushes.
+
+Notes: This API may return a number *larger* than the actual cache
+line, but it will guarantee that one or more cache lines fit exactly
+into the width returned by this call.  It will also always be a power
+of two for easy alignment
+
+void
+dma_sync_single_range(struct device *dev, dma_addr_t dma_handle,
+		      unsigned long offset, size_t size,
+		      enum dma_data_direction direction)
+
+does a partial sync.  starting at offset and continuing for size.  You
+must be careful to observe the cache alignment and width when doing
+anything like this.  You must also be extra careful about accessing
+memory you intend to sync partially.
+
+void
+dma_cache_sync(void *vaddr, size_t size,
+	       enum dma_data_direction direction)
+
+Do a partial sync of memory that was allocated by
+dma_alloc_noncoherent(), starting at virtual address vaddr and
+continuing on for size.  Again, you *must* observe the cache line
+boundaries when doing this.
+
+int
+dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
+			    dma_addr_t device_addr, size_t size, int
+			    flags)
+
+
+Declare region of memory to be handed out by dma_alloc_coherent when
+it's asked for coherent memory for this device.
+
+bus_addr is the physical address to which the memory is currently
+assigned in the bus responding region (this will be used by the
+platform to perform the mapping)
+
+device_addr is the physical address the device needs to be programmed
+with actually to address this memory (this will be handed out as the
+dma_addr_t in dma_alloc_coherent())
+
+size is the size of the area (must be multiples of PAGE_SIZE).
+
+flags can be or'd together and are
+
+DMA_MEMORY_MAP - request that the memory returned from
+dma_alloc_coherent() be directly writeable.
+
+DMA_MEMORY_IO - request that the memory returned from
+dma_alloc_coherent() be addressable using read/write/memcpy_toio etc.
+
+One or both of these flags must be present
+
+DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
+dma_alloc_coherent of any child devices of this one (for memory residing
+on a bridge).
+
+DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions. 
+Do not allow dma_alloc_coherent() to fall back to system memory when
+it's out of memory in the declared region.
+
+The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and
+must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO
+if only DMA_MEMORY_MAP were passed in) for success or zero for
+failure.
+
+Note, for DMA_MEMORY_IO returns, all subsequent memory returned by
+dma_alloc_coherent() may no longer be accessed directly, but instead
+must be accessed using the correct bus functions.  If your driver
+isn't prepared to handle this contingency, it should not specify
+DMA_MEMORY_IO in the input flags.
+
+As a simplification for the platforms, only *one* such region of
+memory may be declared per device.
+
+For reasons of efficiency, most platforms choose to track the declared
+region only at the granularity of a page.  For smaller allocations,
+you should use the dma_pool() API.
+
+void
+dma_release_declared_memory(struct device *dev)
+
+Remove the memory region previously declared from the system.  This
+API performs *no* in-use checking for this region and will return
+unconditionally having removed all the required structures.  It is the
+drivers job to ensure that no parts of this memory region are
+currently in use.
+
+void *
+dma_mark_declared_memory_occupied(struct device *dev,
+				  dma_addr_t device_addr, size_t size)
+
+This is used to occupy specific regions of the declared space
+(dma_alloc_coherent() will hand out the first free region it finds).
+
+device_addr is the *device* address of the region requested
+
+size is the size (and should be a page sized multiple).
+
+The return value will be either a pointer to the processor virtual
+address of the memory, or an error (via PTR_ERR()) if any part of the
+region is occupied.
+
+
diff --git a/Documentation/DMA-mapping.txt b/Documentation/DMA-mapping.txt
new file mode 100644
index 000000000000..f4ac37f157ea
--- /dev/null
+++ b/Documentation/DMA-mapping.txt
@@ -0,0 +1,881 @@
+			Dynamic DMA mapping
+			===================
+
+		 David S. Miller <davem@redhat.com>
+		 Richard Henderson <rth@cygnus.com>
+		  Jakub Jelinek <jakub@redhat.com>
+
+This document describes the DMA mapping system in terms of the pci_
+API.  For a similar API that works for generic devices, see
+DMA-API.txt.
+
+Most of the 64bit platforms have special hardware that translates bus
+addresses (DMA addresses) into physical addresses.  This is similar to
+how page tables and/or a TLB translates virtual addresses to physical
+addresses on a CPU.  This is needed so that e.g. PCI devices can
+access with a Single Address Cycle (32bit DMA address) any page in the
+64bit physical address space.  Previously in Linux those 64bit
+platforms had to set artificial limits on the maximum RAM size in the
+system, so that the virt_to_bus() static scheme works (the DMA address
+translation tables were simply filled on bootup to map each bus
+address to the physical page __pa(bus_to_virt())).
+
+So that Linux can use the dynamic DMA mapping, it needs some help from the
+drivers, namely it has to take into account that DMA addresses should be
+mapped only for the time they are actually used and unmapped after the DMA
+transfer.
+
+The following API will work of course even on platforms where no such
+hardware exists, see e.g. include/asm-i386/pci.h for how it is implemented on
+top of the virt_to_bus interface.
+
+First of all, you should make sure
+
+#include <linux/pci.h>
+
+is in your driver. This file will obtain for you the definition of the
+dma_addr_t (which can hold any valid DMA address for the platform)
+type which should be used everywhere you hold a DMA (bus) address
+returned from the DMA mapping functions.
+
+			 What memory is DMA'able?
+
+The first piece of information you must know is what kernel memory can
+be used with the DMA mapping facilities.  There has been an unwritten
+set of rules regarding this, and this text is an attempt to finally
+write them down.
+
+If you acquired your memory via the page allocator
+(i.e. __get_free_page*()) or the generic memory allocators
+(i.e. kmalloc() or kmem_cache_alloc()) then you may DMA to/from
+that memory using the addresses returned from those routines.
+
+This means specifically that you may _not_ use the memory/addresses
+returned from vmalloc() for DMA.  It is possible to DMA to the
+_underlying_ memory mapped into a vmalloc() area, but this requires
+walking page tables to get the physical addresses, and then
+translating each of those pages back to a kernel address using
+something like __va().  [ EDIT: Update this when we integrate
+Gerd Knorr's generic code which does this. ]
+
+This rule also means that you may not use kernel image addresses
+(ie. items in the kernel's data/text/bss segment, or your driver's)
+nor may you use kernel stack addresses for DMA.  Both of these items
+might be mapped somewhere entirely different than the rest of physical
+memory.
+
+Also, this means that you cannot take the return of a kmap()
+call and DMA to/from that.  This is similar to vmalloc().
+
+What about block I/O and networking buffers?  The block I/O and
+networking subsystems make sure that the buffers they use are valid
+for you to DMA from/to.
+
+			DMA addressing limitations
+
+Does your device have any DMA addressing limitations?  For example, is
+your device only capable of driving the low order 24-bits of address
+on the PCI bus for SAC DMA transfers?  If so, you need to inform the
+PCI layer of this fact.
+
+By default, the kernel assumes that your device can address the full
+32-bits in a SAC cycle.  For a 64-bit DAC capable device, this needs
+to be increased.  And for a device with limitations, as discussed in
+the previous paragraph, it needs to be decreased.
+
+pci_alloc_consistent() by default will return 32-bit DMA addresses.
+PCI-X specification requires PCI-X devices to support 64-bit
+addressing (DAC) for all transactions. And at least one platform (SGI
+SN2) requires 64-bit consistent allocations to operate correctly when
+the IO bus is in PCI-X mode. Therefore, like with pci_set_dma_mask(),
+it's good practice to call pci_set_consistent_dma_mask() to set the
+appropriate mask even if your device only supports 32-bit DMA
+(default) and especially if it's a PCI-X device.
+
+For correct operation, you must interrogate the PCI layer in your
+device probe routine to see if the PCI controller on the machine can
+properly support the DMA addressing limitation your device has.  It is
+good style to do this even if your device holds the default setting,
+because this shows that you did think about these issues wrt. your
+device.
+
+The query is performed via a call to pci_set_dma_mask():
+
+	int pci_set_dma_mask(struct pci_dev *pdev, u64 device_mask);
+
+The query for consistent allocations is performed via a a call to
+pci_set_consistent_dma_mask():
+
+	int pci_set_consistent_dma_mask(struct pci_dev *pdev, u64 device_mask);
+
+Here, pdev is a pointer to the PCI device struct of your device, and
+device_mask is a bit mask describing which bits of a PCI address your
+device supports.  It returns zero if your card can perform DMA
+properly on the machine given the address mask you provided.
+
+If it returns non-zero, your device can not perform DMA properly on
+this platform, and attempting to do so will result in undefined
+behavior.  You must either use a different mask, or not use DMA.
+
+This means that in the failure case, you have three options:
+
+1) Use another DMA mask, if possible (see below).
+2) Use some non-DMA mode for data transfer, if possible.
+3) Ignore this device and do not initialize it.
+
+It is recommended that your driver print a kernel KERN_WARNING message
+when you end up performing either #2 or #3.  In this manner, if a user
+of your driver reports that performance is bad or that the device is not
+even detected, you can ask them for the kernel messages to find out
+exactly why.
+
+The standard 32-bit addressing PCI device would do something like
+this:
+
+	if (pci_set_dma_mask(pdev, DMA_32BIT_MASK)) {
+		printk(KERN_WARNING
+		       "mydev: No suitable DMA available.\n");
+		goto ignore_this_device;
+	}
+
+Another common scenario is a 64-bit capable device.  The approach
+here is to try for 64-bit DAC addressing, but back down to a
+32-bit mask should that fail.  The PCI platform code may fail the
+64-bit mask not because the platform is not capable of 64-bit
+addressing.  Rather, it may fail in this case simply because
+32-bit SAC addressing is done more efficiently than DAC addressing.
+Sparc64 is one platform which behaves in this way.
+
+Here is how you would handle a 64-bit capable device which can drive
+all 64-bits when accessing streaming DMA:
+
+	int using_dac;
+
+	if (!pci_set_dma_mask(pdev, DMA_64BIT_MASK)) {
+		using_dac = 1;
+	} else if (!pci_set_dma_mask(pdev, DMA_32BIT_MASK)) {
+		using_dac = 0;
+	} else {
+		printk(KERN_WARNING
+		       "mydev: No suitable DMA available.\n");
+		goto ignore_this_device;
+	}
+
+If a card is capable of using 64-bit consistent allocations as well,
+the case would look like this:
+
+	int using_dac, consistent_using_dac;
+
+	if (!pci_set_dma_mask(pdev, DMA_64BIT_MASK)) {
+		using_dac = 1;
+	   	consistent_using_dac = 1;
+		pci_set_consistent_dma_mask(pdev, DMA_64BIT_MASK);
+	} else if (!pci_set_dma_mask(pdev, DMA_32BIT_MASK)) {
+		using_dac = 0;
+		consistent_using_dac = 0;
+		pci_set_consistent_dma_mask(pdev, DMA_32BIT_MASK);
+	} else {
+		printk(KERN_WARNING
+		       "mydev: No suitable DMA available.\n");
+		goto ignore_this_device;
+	}
+
+pci_set_consistent_dma_mask() will always be able to set the same or a
+smaller mask as pci_set_dma_mask(). However for the rare case that a
+device driver only uses consistent allocations, one would have to
+check the return value from pci_set_consistent_dma_mask().
+
+If your 64-bit device is going to be an enormous consumer of DMA
+mappings, this can be problematic since the DMA mappings are a
+finite resource on many platforms.  Please see the "DAC Addressing
+for Address Space Hungry Devices" section near the end of this
+document for how to handle this case.
+
+Finally, if your device can only drive the low 24-bits of
+address during PCI bus mastering you might do something like:
+
+	if (pci_set_dma_mask(pdev, 0x00ffffff)) {
+		printk(KERN_WARNING
+		       "mydev: 24-bit DMA addressing not available.\n");
+		goto ignore_this_device;
+	}
+
+When pci_set_dma_mask() is successful, and returns zero, the PCI layer
+saves away this mask you have provided.  The PCI layer will use this
+information later when you make DMA mappings.
+
+There is a case which we are aware of at this time, which is worth
+mentioning in this documentation.  If your device supports multiple
+functions (for example a sound card provides playback and record
+functions) and the various different functions have _different_
+DMA addressing limitations, you may wish to probe each mask and
+only provide the functionality which the machine can handle.  It
+is important that the last call to pci_set_dma_mask() be for the 
+most specific mask.
+
+Here is pseudo-code showing how this might be done:
+
+	#define PLAYBACK_ADDRESS_BITS	DMA_32BIT_MASK
+	#define RECORD_ADDRESS_BITS	0x00ffffff
+
+	struct my_sound_card *card;
+	struct pci_dev *pdev;
+
+	...
+	if (!pci_set_dma_mask(pdev, PLAYBACK_ADDRESS_BITS)) {
+		card->playback_enabled = 1;
+	} else {
+		card->playback_enabled = 0;
+		printk(KERN_WARN "%s: Playback disabled due to DMA limitations.\n",
+		       card->name);
+	}
+	if (!pci_set_dma_mask(pdev, RECORD_ADDRESS_BITS)) {
+		card->record_enabled = 1;
+	} else {
+		card->record_enabled = 0;
+		printk(KERN_WARN "%s: Record disabled due to DMA limitations.\n",
+		       card->name);
+	}
+
+A sound card was used as an example here because this genre of PCI
+devices seems to be littered with ISA chips given a PCI front end,
+and thus retaining the 16MB DMA addressing limitations of ISA.
+
+			Types of DMA mappings
+
+There are two types of DMA mappings:
+
+- Consistent DMA mappings which are usually mapped at driver
+  initialization, unmapped at the end and for which the hardware should
+  guarantee that the device and the CPU can access the data
+  in parallel and will see updates made by each other without any
+  explicit software flushing.
+
+  Think of "consistent" as "synchronous" or "coherent".
+
+  The current default is to return consistent memory in the low 32
+  bits of the PCI bus space.  However, for future compatibility you
+  should set the consistent mask even if this default is fine for your
+  driver.
+
+  Good examples of what to use consistent mappings for are:
+
+	- Network card DMA ring descriptors.
+	- SCSI adapter mailbox command data structures.
+	- Device firmware microcode executed out of
+	  main memory.
+
+  The invariant these examples all require is that any CPU store
+  to memory is immediately visible to the device, and vice
+  versa.  Consistent mappings guarantee this.
+
+  IMPORTANT: Consistent DMA memory does not preclude the usage of
+             proper memory barriers.  The CPU may reorder stores to
+	     consistent memory just as it may normal memory.  Example:
+	     if it is important for the device to see the first word
+	     of a descriptor updated before the second, you must do
+	     something like:
+
+		desc->word0 = address;
+		wmb();
+		desc->word1 = DESC_VALID;
+
+             in order to get correct behavior on all platforms.
+
+- Streaming DMA mappings which are usually mapped for one DMA transfer,
+  unmapped right after it (unless you use pci_dma_sync_* below) and for which
+  hardware can optimize for sequential accesses.
+
+  This of "streaming" as "asynchronous" or "outside the coherency
+  domain".
+
+  Good examples of what to use streaming mappings for are:
+
+	- Networking buffers transmitted/received by a device.
+	- Filesystem buffers written/read by a SCSI device.
+
+  The interfaces for using this type of mapping were designed in
+  such a way that an implementation can make whatever performance
+  optimizations the hardware allows.  To this end, when using
+  such mappings you must be explicit about what you want to happen.
+
+Neither type of DMA mapping has alignment restrictions that come
+from PCI, although some devices may have such restrictions.
+
+		 Using Consistent DMA mappings.
+
+To allocate and map large (PAGE_SIZE or so) consistent DMA regions,
+you should do:
+
+	dma_addr_t dma_handle;
+
+	cpu_addr = pci_alloc_consistent(dev, size, &dma_handle);
+
+where dev is a struct pci_dev *. You should pass NULL for PCI like buses
+where devices don't have struct pci_dev (like ISA, EISA).  This may be
+called in interrupt context. 
+
+This argument is needed because the DMA translations may be bus
+specific (and often is private to the bus which the device is attached
+to).
+
+Size is the length of the region you want to allocate, in bytes.
+
+This routine will allocate RAM for that region, so it acts similarly to
+__get_free_pages (but takes size instead of a page order).  If your
+driver needs regions sized smaller than a page, you may prefer using
+the pci_pool interface, described below.
+
+The consistent DMA mapping interfaces, for non-NULL dev, will by
+default return a DMA address which is SAC (Single Address Cycle)
+addressable.  Even if the device indicates (via PCI dma mask) that it
+may address the upper 32-bits and thus perform DAC cycles, consistent
+allocation will only return > 32-bit PCI addresses for DMA if the
+consistent dma mask has been explicitly changed via
+pci_set_consistent_dma_mask().  This is true of the pci_pool interface
+as well.
+
+pci_alloc_consistent returns two values: the virtual address which you
+can use to access it from the CPU and dma_handle which you pass to the
+card.
+
+The cpu return address and the DMA bus master address are both
+guaranteed to be aligned to the smallest PAGE_SIZE order which
+is greater than or equal to the requested size.  This invariant
+exists (for example) to guarantee that if you allocate a chunk
+which is smaller than or equal to 64 kilobytes, the extent of the
+buffer you receive will not cross a 64K boundary.
+
+To unmap and free such a DMA region, you call:
+
+	pci_free_consistent(dev, size, cpu_addr, dma_handle);
+
+where dev, size are the same as in the above call and cpu_addr and
+dma_handle are the values pci_alloc_consistent returned to you.
+This function may not be called in interrupt context.
+
+If your driver needs lots of smaller memory regions, you can write
+custom code to subdivide pages returned by pci_alloc_consistent,
+or you can use the pci_pool API to do that.  A pci_pool is like
+a kmem_cache, but it uses pci_alloc_consistent not __get_free_pages.
+Also, it understands common hardware constraints for alignment,
+like queue heads needing to be aligned on N byte boundaries.
+
+Create a pci_pool like this:
+
+	struct pci_pool *pool;
+
+	pool = pci_pool_create(name, dev, size, align, alloc);
+
+The "name" is for diagnostics (like a kmem_cache name); dev and size
+are as above.  The device's hardware alignment requirement for this
+type of data is "align" (which is expressed in bytes, and must be a
+power of two).  If your device has no boundary crossing restrictions,
+pass 0 for alloc; passing 4096 says memory allocated from this pool
+must not cross 4KByte boundaries (but at that time it may be better to
+go for pci_alloc_consistent directly instead).
+
+Allocate memory from a pci pool like this:
+
+	cpu_addr = pci_pool_alloc(pool, flags, &dma_handle);
+
+flags are SLAB_KERNEL if blocking is permitted (not in_interrupt nor
+holding SMP locks), SLAB_ATOMIC otherwise.  Like pci_alloc_consistent,
+this returns two values, cpu_addr and dma_handle.
+
+Free memory that was allocated from a pci_pool like this:
+
+	pci_pool_free(pool, cpu_addr, dma_handle);
+
+where pool is what you passed to pci_pool_alloc, and cpu_addr and
+dma_handle are the values pci_pool_alloc returned. This function
+may be called in interrupt context.
+
+Destroy a pci_pool by calling:
+
+	pci_pool_destroy(pool);
+
+Make sure you've called pci_pool_free for all memory allocated
+from a pool before you destroy the pool. This function may not
+be called in interrupt context.
+
+			DMA Direction
+
+The interfaces described in subsequent portions of this document
+take a DMA direction argument, which is an integer and takes on
+one of the following values:
+
+ PCI_DMA_BIDIRECTIONAL
+ PCI_DMA_TODEVICE
+ PCI_DMA_FROMDEVICE
+ PCI_DMA_NONE
+
+One should provide the exact DMA direction if you know it.
+
+PCI_DMA_TODEVICE means "from main memory to the PCI device"
+PCI_DMA_FROMDEVICE means "from the PCI device to main memory"
+It is the direction in which the data moves during the DMA
+transfer.
+
+You are _strongly_ encouraged to specify this as precisely
+as you possibly can.
+
+If you absolutely cannot know the direction of the DMA transfer,
+specify PCI_DMA_BIDIRECTIONAL.  It means that the DMA can go in
+either direction.  The platform guarantees that you may legally
+specify this, and that it will work, but this may be at the
+cost of performance for example.
+
+The value PCI_DMA_NONE is to be used for debugging.  One can
+hold this in a data structure before you come to know the
+precise direction, and this will help catch cases where your
+direction tracking logic has failed to set things up properly.
+
+Another advantage of specifying this value precisely (outside of
+potential platform-specific optimizations of such) is for debugging.
+Some platforms actually have a write permission boolean which DMA
+mappings can be marked with, much like page protections in the user
+program address space.  Such platforms can and do report errors in the
+kernel logs when the PCI controller hardware detects violation of the
+permission setting.
+
+Only streaming mappings specify a direction, consistent mappings
+implicitly have a direction attribute setting of
+PCI_DMA_BIDIRECTIONAL.
+
+The SCSI subsystem provides mechanisms for you to easily obtain
+the direction to use, in the SCSI command:
+
+	scsi_to_pci_dma_dir(SCSI_DIRECTION)
+
+Where SCSI_DIRECTION is obtained from the 'sc_data_direction'
+member of the SCSI command your driver is working on.  The
+mentioned interface above returns a value suitable for passing
+into the streaming DMA mapping interfaces below.
+
+For Networking drivers, it's a rather simple affair.  For transmit
+packets, map/unmap them with the PCI_DMA_TODEVICE direction
+specifier.  For receive packets, just the opposite, map/unmap them
+with the PCI_DMA_FROMDEVICE direction specifier.
+
+		  Using Streaming DMA mappings
+
+The streaming DMA mapping routines can be called from interrupt
+context.  There are two versions of each map/unmap, one which will
+map/unmap a single memory region, and one which will map/unmap a
+scatterlist.
+
+To map a single region, you do:
+
+	struct pci_dev *pdev = mydev->pdev;
+	dma_addr_t dma_handle;
+	void *addr = buffer->ptr;
+	size_t size = buffer->len;
+
+	dma_handle = pci_map_single(dev, addr, size, direction);
+
+and to unmap it:
+
+	pci_unmap_single(dev, dma_handle, size, direction);
+
+You should call pci_unmap_single when the DMA activity is finished, e.g.
+from the interrupt which told you that the DMA transfer is done.
+
+Using cpu pointers like this for single mappings has a disadvantage,
+you cannot reference HIGHMEM memory in this way.  Thus, there is a
+map/unmap interface pair akin to pci_{map,unmap}_single.  These
+interfaces deal with page/offset pairs instead of cpu pointers.
+Specifically:
+
+	struct pci_dev *pdev = mydev->pdev;
+	dma_addr_t dma_handle;
+	struct page *page = buffer->page;
+	unsigned long offset = buffer->offset;
+	size_t size = buffer->len;
+
+	dma_handle = pci_map_page(dev, page, offset, size, direction);
+
+	...
+
+	pci_unmap_page(dev, dma_handle, size, direction);
+
+Here, "offset" means byte offset within the given page.
+
+With scatterlists, you map a region gathered from several regions by:
+
+	int i, count = pci_map_sg(dev, sglist, nents, direction);
+	struct scatterlist *sg;
+
+	for (i = 0, sg = sglist; i < count; i++, sg++) {
+		hw_address[i] = sg_dma_address(sg);
+		hw_len[i] = sg_dma_len(sg);
+	}
+
+where nents is the number of entries in the sglist.
+
+The implementation is free to merge several consecutive sglist entries
+into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any
+consecutive sglist entries can be merged into one provided the first one
+ends and the second one starts on a page boundary - in fact this is a huge
+advantage for cards which either cannot do scatter-gather or have very
+limited number of scatter-gather entries) and returns the actual number
+of sg entries it mapped them to. On failure 0 is returned.
+
+Then you should loop count times (note: this can be less than nents times)
+and use sg_dma_address() and sg_dma_len() macros where you previously
+accessed sg->address and sg->length as shown above.
+
+To unmap a scatterlist, just call:
+
+	pci_unmap_sg(dev, sglist, nents, direction);
+
+Again, make sure DMA activity has already finished.
+
+PLEASE NOTE:  The 'nents' argument to the pci_unmap_sg call must be
+              the _same_ one you passed into the pci_map_sg call,
+	      it should _NOT_ be the 'count' value _returned_ from the
+              pci_map_sg call.
+
+Every pci_map_{single,sg} call should have its pci_unmap_{single,sg}
+counterpart, because the bus address space is a shared resource (although
+in some ports the mapping is per each BUS so less devices contend for the
+same bus address space) and you could render the machine unusable by eating
+all bus addresses.
+
+If you need to use the same streaming DMA region multiple times and touch
+the data in between the DMA transfers, the buffer needs to be synced
+properly in order for the cpu and device to see the most uptodate and
+correct copy of the DMA buffer.
+
+So, firstly, just map it with pci_map_{single,sg}, and after each DMA
+transfer call either:
+
+	pci_dma_sync_single_for_cpu(dev, dma_handle, size, direction);
+
+or:
+
+	pci_dma_sync_sg_for_cpu(dev, sglist, nents, direction);
+
+as appropriate.
+
+Then, if you wish to let the device get at the DMA area again,
+finish accessing the data with the cpu, and then before actually
+giving the buffer to the hardware call either:
+
+	pci_dma_sync_single_for_device(dev, dma_handle, size, direction);
+
+or:
+
+	pci_dma_sync_sg_for_device(dev, sglist, nents, direction);
+
+as appropriate.
+
+After the last DMA transfer call one of the DMA unmap routines
+pci_unmap_{single,sg}. If you don't touch the data from the first pci_map_*
+call till pci_unmap_*, then you don't have to call the pci_dma_sync_*
+routines at all.
+
+Here is pseudo code which shows a situation in which you would need
+to use the pci_dma_sync_*() interfaces.
+
+	my_card_setup_receive_buffer(struct my_card *cp, char *buffer, int len)
+	{
+		dma_addr_t mapping;
+
+		mapping = pci_map_single(cp->pdev, buffer, len, PCI_DMA_FROMDEVICE);
+
+		cp->rx_buf = buffer;
+		cp->rx_len = len;
+		cp->rx_dma = mapping;
+
+		give_rx_buf_to_card(cp);
+	}
+
+	...
+
+	my_card_interrupt_handler(int irq, void *devid, struct pt_regs *regs)
+	{
+		struct my_card *cp = devid;
+
+		...
+		if (read_card_status(cp) == RX_BUF_TRANSFERRED) {
+			struct my_card_header *hp;
+
+			/* Examine the header to see if we wish
+			 * to accept the data.  But synchronize
+			 * the DMA transfer with the CPU first
+			 * so that we see updated contents.
+			 */
+			pci_dma_sync_single_for_cpu(cp->pdev, cp->rx_dma,
+						    cp->rx_len,
+						    PCI_DMA_FROMDEVICE);
+
+			/* Now it is safe to examine the buffer. */
+			hp = (struct my_card_header *) cp->rx_buf;
+			if (header_is_ok(hp)) {
+				pci_unmap_single(cp->pdev, cp->rx_dma, cp->rx_len,
+						 PCI_DMA_FROMDEVICE);
+				pass_to_upper_layers(cp->rx_buf);
+				make_and_setup_new_rx_buf(cp);
+			} else {
+				/* Just sync the buffer and give it back
+				 * to the card.
+				 */
+				pci_dma_sync_single_for_device(cp->pdev,
+							       cp->rx_dma,
+							       cp->rx_len,
+							       PCI_DMA_FROMDEVICE);
+				give_rx_buf_to_card(cp);
+			}
+		}
+	}
+
+Drivers converted fully to this interface should not use virt_to_bus any
+longer, nor should they use bus_to_virt. Some drivers have to be changed a
+little bit, because there is no longer an equivalent to bus_to_virt in the
+dynamic DMA mapping scheme - you have to always store the DMA addresses
+returned by the pci_alloc_consistent, pci_pool_alloc, and pci_map_single
+calls (pci_map_sg stores them in the scatterlist itself if the platform
+supports dynamic DMA mapping in hardware) in your driver structures and/or
+in the card registers.
+
+All PCI drivers should be using these interfaces with no exceptions.
+It is planned to completely remove virt_to_bus() and bus_to_virt() as
+they are entirely deprecated.  Some ports already do not provide these
+as it is impossible to correctly support them.
+
+		64-bit DMA and DAC cycle support
+
+Do you understand all of the text above?  Great, then you already
+know how to use 64-bit DMA addressing under Linux.  Simply make
+the appropriate pci_set_dma_mask() calls based upon your cards
+capabilities, then use the mapping APIs above.
+
+It is that simple.
+
+Well, not for some odd devices.  See the next section for information
+about that.
+
+	DAC Addressing for Address Space Hungry Devices
+
+There exists a class of devices which do not mesh well with the PCI
+DMA mapping API.  By definition these "mappings" are a finite
+resource.  The number of total available mappings per bus is platform
+specific, but there will always be a reasonable amount.
+
+What is "reasonable"?  Reasonable means that networking and block I/O
+devices need not worry about using too many mappings.
+
+As an example of a problematic device, consider compute cluster cards.
+They can potentially need to access gigabytes of memory at once via
+DMA.  Dynamic mappings are unsuitable for this kind of access pattern.
+
+To this end we've provided a small API by which a device driver
+may use DAC cycles to directly address all of physical memory.
+Not all platforms support this, but most do.  It is easy to determine
+whether the platform will work properly at probe time.
+
+First, understand that there may be a SEVERE performance penalty for
+using these interfaces on some platforms.  Therefore, you MUST only
+use these interfaces if it is absolutely required.  %99 of devices can
+use the normal APIs without any problems.
+
+Note that for streaming type mappings you must either use these
+interfaces, or the dynamic mapping interfaces above.  You may not mix
+usage of both for the same device.  Such an act is illegal and is
+guaranteed to put a banana in your tailpipe.
+
+However, consistent mappings may in fact be used in conjunction with
+these interfaces.  Remember that, as defined, consistent mappings are
+always going to be SAC addressable.
+
+The first thing your driver needs to do is query the PCI platform
+layer with your devices DAC addressing capabilities:
+
+	int pci_dac_set_dma_mask(struct pci_dev *pdev, u64 mask);
+
+This routine behaves identically to pci_set_dma_mask.  You may not
+use the following interfaces if this routine fails.
+
+Next, DMA addresses using this API are kept track of using the
+dma64_addr_t type.  It is guaranteed to be big enough to hold any
+DAC address the platform layer will give to you from the following
+routines.  If you have consistent mappings as well, you still
+use plain dma_addr_t to keep track of those.
+
+All mappings obtained here will be direct.  The mappings are not
+translated, and this is the purpose of this dialect of the DMA API.
+
+All routines work with page/offset pairs.  This is the _ONLY_ way to 
+portably refer to any piece of memory.  If you have a cpu pointer
+(which may be validly DMA'd too) you may easily obtain the page
+and offset using something like this:
+
+	struct page *page = virt_to_page(ptr);
+	unsigned long offset = offset_in_page(ptr);
+
+Here are the interfaces:
+
+	dma64_addr_t pci_dac_page_to_dma(struct pci_dev *pdev,
+					 struct page *page,
+					 unsigned long offset,
+					 int direction);
+
+The DAC address for the tuple PAGE/OFFSET are returned.  The direction
+argument is the same as for pci_{map,unmap}_single().  The same rules
+for cpu/device access apply here as for the streaming mapping
+interfaces.  To reiterate:
+
+	The cpu may touch the buffer before pci_dac_page_to_dma.
+	The device may touch the buffer after pci_dac_page_to_dma
+	is made, but the cpu may NOT.
+
+When the DMA transfer is complete, invoke:
+
+	void pci_dac_dma_sync_single_for_cpu(struct pci_dev *pdev,
+					     dma64_addr_t dma_addr,
+					     size_t len, int direction);
+
+This must be done before the CPU looks at the buffer again.
+This interface behaves identically to pci_dma_sync_{single,sg}_for_cpu().
+
+And likewise, if you wish to let the device get back at the buffer after
+the cpu has read/written it, invoke:
+
+	void pci_dac_dma_sync_single_for_device(struct pci_dev *pdev,
+						dma64_addr_t dma_addr,
+						size_t len, int direction);
+
+before letting the device access the DMA area again.
+
+If you need to get back to the PAGE/OFFSET tuple from a dma64_addr_t
+the following interfaces are provided:
+
+	struct page *pci_dac_dma_to_page(struct pci_dev *pdev,
+					 dma64_addr_t dma_addr);
+	unsigned long pci_dac_dma_to_offset(struct pci_dev *pdev,
+					    dma64_addr_t dma_addr);
+
+This is possible with the DAC interfaces purely because they are
+not translated in any way.
+
+		Optimizing Unmap State Space Consumption
+
+On many platforms, pci_unmap_{single,page}() is simply a nop.
+Therefore, keeping track of the mapping address and length is a waste
+of space.  Instead of filling your drivers up with ifdefs and the like
+to "work around" this (which would defeat the whole purpose of a
+portable API) the following facilities are provided.
+
+Actually, instead of describing the macros one by one, we'll
+transform some example code.
+
+1) Use DECLARE_PCI_UNMAP_{ADDR,LEN} in state saving structures.
+   Example, before:
+
+	struct ring_state {
+		struct sk_buff *skb;
+		dma_addr_t mapping;
+		__u32 len;
+	};
+
+   after:
+
+	struct ring_state {
+		struct sk_buff *skb;
+		DECLARE_PCI_UNMAP_ADDR(mapping)
+		DECLARE_PCI_UNMAP_LEN(len)
+	};
+
+   NOTE: DO NOT put a semicolon at the end of the DECLARE_*()
+         macro.
+
+2) Use pci_unmap_{addr,len}_set to set these values.
+   Example, before:
+
+	ringp->mapping = FOO;
+	ringp->len = BAR;
+
+   after:
+
+	pci_unmap_addr_set(ringp, mapping, FOO);
+	pci_unmap_len_set(ringp, len, BAR);
+
+3) Use pci_unmap_{addr,len} to access these values.
+   Example, before:
+
+	pci_unmap_single(pdev, ringp->mapping, ringp->len,
+			 PCI_DMA_FROMDEVICE);
+
+   after:
+
+	pci_unmap_single(pdev,
+			 pci_unmap_addr(ringp, mapping),
+			 pci_unmap_len(ringp, len),
+			 PCI_DMA_FROMDEVICE);
+
+It really should be self-explanatory.  We treat the ADDR and LEN
+separately, because it is possible for an implementation to only
+need the address in order to perform the unmap operation.
+
+			Platform Issues
+
+If you are just writing drivers for Linux and do not maintain
+an architecture port for the kernel, you can safely skip down
+to "Closing".
+
+1) Struct scatterlist requirements.
+
+   Struct scatterlist must contain, at a minimum, the following
+   members:
+
+	struct page *page;
+	unsigned int offset;
+	unsigned int length;
+
+   The base address is specified by a "page+offset" pair.
+
+   Previous versions of struct scatterlist contained a "void *address"
+   field that was sometimes used instead of page+offset.  As of Linux
+   2.5., page+offset is always used, and the "address" field has been
+   deleted.
+
+2) More to come...
+
+			Handling Errors
+
+DMA address space is limited on some architectures and an allocation
+failure can be determined by:
+
+- checking if pci_alloc_consistent returns NULL or pci_map_sg returns 0
+
+- checking the returned dma_addr_t of pci_map_single and pci_map_page
+  by using pci_dma_mapping_error():
+
+	dma_addr_t dma_handle;
+
+	dma_handle = pci_map_single(dev, addr, size, direction);
+	if (pci_dma_mapping_error(dma_handle)) {
+		/*
+		 * reduce current DMA mapping usage,
+		 * delay and try again later or
+		 * reset driver.
+		 */
+	}
+
+			   Closing
+
+This document, and the API itself, would not be in it's current
+form without the feedback and suggestions from numerous individuals.
+We would like to specifically mention, in no particular order, the
+following people:
+
+	Russell King <rmk@arm.linux.org.uk>
+	Leo Dagum <dagum@barrel.engr.sgi.com>
+	Ralf Baechle <ralf@oss.sgi.com>
+	Grant Grundler <grundler@cup.hp.com>
+	Jay Estabrook <Jay.Estabrook@compaq.com>
+	Thomas Sailer <sailer@ife.ee.ethz.ch>
+	Andrea Arcangeli <andrea@suse.de>
+	Jens Axboe <axboe@suse.de>
+	David Mosberger-Tang <davidm@hpl.hp.com>
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
new file mode 100644
index 000000000000..a221039ee4c9
--- /dev/null
+++ b/Documentation/DocBook/Makefile
@@ -0,0 +1,195 @@
+###
+# This makefile is used to generate the kernel documentation,
+# primarily based on in-line comments in various source files.
+# See Documentation/kernel-doc-nano-HOWTO.txt for instruction in how
+# to ducument the SRC - and how to read it.
+# To add a new book the only step required is to add the book to the
+# list of DOCBOOKS.
+
+DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \
+	    kernel-hacking.xml kernel-locking.xml via-audio.xml \
+	    deviceiobook.xml procfs-guide.xml tulip-user.xml \
+	    writing_usb_driver.xml scsidrivers.xml sis900.xml \
+	    kernel-api.xml journal-api.xml lsm.xml usb.xml \
+	    gadget.xml libata.xml mtdnand.xml librs.xml
+
+###
+# The build process is as follows (targets):
+#              (xmldocs)
+# file.tmpl --> file.xml +--> file.ps   (psdocs)
+#                        +--> file.pdf  (pdfdocs)
+#                        +--> DIR=file  (htmldocs)
+#                        +--> man/      (mandocs)
+
+###
+# The targets that may be used.
+.PHONY:	xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs
+
+BOOKS := $(addprefix $(obj)/,$(DOCBOOKS))
+xmldocs: $(BOOKS)
+sgmldocs: xmldocs
+
+PS := $(patsubst %.xml, %.ps, $(BOOKS))
+psdocs: $(PS)
+
+PDF := $(patsubst %.xml, %.pdf, $(BOOKS))
+pdfdocs: $(PDF)
+
+HTML := $(patsubst %.xml, %.html, $(BOOKS))
+htmldocs: $(HTML)
+
+MAN := $(patsubst %.xml, %.9, $(BOOKS))
+mandocs: $(MAN)
+
+installmandocs: mandocs
+	$(MAKEMAN) install Documentation/DocBook/man
+
+###
+#External programs used
+KERNELDOC = scripts/kernel-doc
+DOCPROC   = scripts/basic/docproc
+SPLITMAN  = $(PERL) $(srctree)/scripts/split-man
+MAKEMAN   = $(PERL) $(srctree)/scripts/makeman
+
+###
+# DOCPROC is used for two purposes:
+# 1) To generate a dependency list for a .tmpl file
+# 2) To preprocess a .tmpl file and call kernel-doc with
+#     appropriate parameters.
+# The following rules are used to generate the .xml documentation
+# required to generate the final targets. (ps, pdf, html).
+quiet_cmd_docproc = DOCPROC $@
+      cmd_docproc = SRCTREE=$(srctree)/ $(DOCPROC) doc $< >$@
+define rule_docproc
+	set -e;								\
+        $(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))';) 	\
+        $(cmd_$(1)); 							\
+        ( 								\
+          echo 'cmd_$@ := $(cmd_$(1))'; 				\
+          echo $@: `SRCTREE=$(srctree) $(DOCPROC) depend $<`; 		\
+        ) > $(dir $@).$(notdir $@).cmd
+endef
+
+%.xml: %.tmpl FORCE
+	$(call if_changed_rule,docproc)
+
+###
+#Read in all saved dependency files 
+cmd_files := $(wildcard $(foreach f,$(BOOKS),$(dir $(f)).$(notdir $(f)).cmd))
+
+ifneq ($(cmd_files),)
+  include $(cmd_files)
+endif
+
+###
+# Changes in kernel-doc force a rebuild of all documentation
+$(BOOKS): $(KERNELDOC)
+
+###
+# procfs guide uses a .c file as example code.
+# This requires an explicit dependency
+C-procfs-example = procfs_example.xml
+C-procfs-example2 = $(addprefix $(obj)/,$(C-procfs-example))
+$(obj)/procfs-guide.xml: $(C-procfs-example2)
+
+###
+# Rules to generate postscript, PDF and HTML
+# db2html creates a directory. Generate a html file used for timestamp
+
+quiet_cmd_db2ps = DB2PS   $@
+      cmd_db2ps = db2ps -o $(dir $@) $<
+%.ps : %.xml
+	@(which db2ps > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	$(call cmd,db2ps)
+
+quiet_cmd_db2pdf = DB2PDF  $@
+      cmd_db2pdf = db2pdf -o $(dir $@) $<
+%.pdf : %.xml
+	@(which db2pdf > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	$(call cmd,db2pdf)
+
+quiet_cmd_db2html = DB2HTML $@
+      cmd_db2html = db2html -o $(patsubst %.html,%,$@) $< &&		      \
+		echo '<a HREF="$(patsubst %.html,%,$(notdir $@))/book1.html"> \
+         Goto $(patsubst %.html,%,$(notdir $@))</a><p>' > $@
+
+%.html:	%.xml
+	@(which db2html > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	@rm -rf $@ $(patsubst %.html,%,$@)
+	$(call cmd,db2html)
+	@if [ ! -z "$(PNG-$(basename $(notdir $@)))" ]; then \
+            cp $(PNG-$(basename $(notdir $@))) $(patsubst %.html,%,$@); fi
+
+###
+# Rule to generate man files - output is placed in the man subdirectory
+
+%.9:	%.xml
+ifneq ($(KBUILD_SRC),)
+	$(Q)mkdir -p $(objtree)/Documentation/DocBook/man
+endif
+	$(SPLITMAN) $< $(objtree)/Documentation/DocBook/man "$(VERSION).$(PATCHLEVEL).$(SUBLEVEL)"
+	$(MAKEMAN) convert $(objtree)/Documentation/DocBook/man $<
+
+###
+# Rules to generate postscripts and PNG imgages from .fig format files
+quiet_cmd_fig2eps = FIG2EPS $@
+      cmd_fig2eps = fig2dev -Leps $< $@
+
+%.eps: %.fig
+	@(which fig2dev > /dev/null 2>&1) || \
+	 (echo "*** You need to install transfig ***"; \
+	  exit 1)
+	$(call cmd,fig2eps)
+
+quiet_cmd_fig2png = FIG2PNG $@
+      cmd_fig2png = fig2dev -Lpng $< $@
+
+%.png: %.fig
+	@(which fig2dev > /dev/null 2>&1) || \
+	 (echo "*** You need to install transfig ***"; \
+	  exit 1)
+	$(call cmd,fig2png)
+
+###
+# Rule to convert a .c file to inline XML documentation
+%.xml: %.c
+	@echo '  GEN     $@'
+	@(                            \
+	   echo "<programlisting>";   \
+	   expand --tabs=8 < $< |     \
+	   sed -e "s/&/\\&amp;/g"     \
+	       -e "s/</\\&lt;/g"      \
+	       -e "s/>/\\&gt;/g";     \
+	   echo "</programlisting>")  > $@
+
+###
+# Help targets as used by the top-level makefile
+dochelp:
+	@echo  '  Linux kernel internal documentation in different formats:'
+	@echo  '  xmldocs (XML DocBook), psdocs (Postscript), pdfdocs (PDF)'
+	@echo  '  htmldocs (HTML), mandocs (man pages, use installmandocs to install)'
+
+###
+# Temporary files left by various tools
+clean-files := $(DOCBOOKS) \
+	$(patsubst %.xml, %.dvi,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.aux,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.tex,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.log,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.out,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.ps,   $(DOCBOOKS)) \
+	$(patsubst %.xml, %.pdf,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.html, $(DOCBOOKS)) \
+	$(patsubst %.xml, %.9,    $(DOCBOOKS)) \
+	$(C-procfs-example)
+
+clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS))
+
+#man put files in man subdir - traverse down
+subdir- := man/
diff --git a/Documentation/DocBook/deviceiobook.tmpl b/Documentation/DocBook/deviceiobook.tmpl
new file mode 100644
index 000000000000..6f41f2f5c6f6
--- /dev/null
+++ b/Documentation/DocBook/deviceiobook.tmpl
@@ -0,0 +1,341 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="DoingIO">
+ <bookinfo>
+  <title>Bus-Independent Device Accesses</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Matthew</firstname>
+    <surname>Wilcox</surname>
+    <affiliation>
+     <address>
+      <email>matthew@wil.cx</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <authorgroup>
+   <author>
+    <firstname>Alan</firstname>
+    <surname>Cox</surname>
+    <affiliation>
+     <address>
+      <email>alan@redhat.com</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2001</year>
+   <holder>Matthew Wilcox</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="intro">
+      <title>Introduction</title>
+  <para>
+	Linux provides an API which abstracts performing IO across all busses
+	and devices, allowing device drivers to be written independently of
+	bus type.
+  </para>
+  </chapter>
+
+  <chapter id="bugs">
+     <title>Known Bugs And Assumptions</title>
+  <para>
+	None.	
+  </para>
+  </chapter>
+
+  <chapter id="mmio">
+    <title>Memory Mapped IO</title>
+    <sect1>
+      <title>Getting Access to the Device</title>
+      <para>
+	The most widely supported form of IO is memory mapped IO.
+	That is, a part of the CPU's address space is interpreted
+	not as accesses to memory, but as accesses to a device.  Some
+	architectures define devices to be at a fixed address, but most
+	have some method of discovering devices.  The PCI bus walk is a
+	good example of such a scheme.	This document does not cover how
+	to receive such an address, but assumes you are starting with one.
+	Physical addresses are of type unsigned long. 
+      </para>
+
+      <para>
+	This address should not be used directly.  Instead, to get an
+	address suitable for passing to the accessor functions described
+	below, you should call <function>ioremap</function>.
+	An address suitable for accessing the device will be returned to you.
+      </para>
+
+      <para>
+	After you've finished using the device (say, in your module's
+	exit routine), call <function>iounmap</function> in order to return
+	the address space to the kernel.  Most architectures allocate new
+	address space each time you call <function>ioremap</function>, and
+	they can run out unless you call <function>iounmap</function>.
+      </para>
+    </sect1>
+
+    <sect1>
+      <title>Accessing the device</title>
+      <para>
+	The part of the interface most used by drivers is reading and
+	writing memory-mapped registers on the device.	Linux provides
+	interfaces to read and write 8-bit, 16-bit, 32-bit and 64-bit
+	quantities.  Due to a historical accident, these are named byte,
+	word, long and quad accesses.  Both read and write accesses are
+	supported; there is no prefetch support at this time.
+      </para>
+
+      <para>
+	The functions are named <function>readb</function>,
+	<function>readw</function>, <function>readl</function>,
+	<function>readq</function>, <function>readb_relaxed</function>,
+	<function>readw_relaxed</function>, <function>readl_relaxed</function>,
+	<function>readq_relaxed</function>, <function>writeb</function>,
+	<function>writew</function>, <function>writel</function> and
+	<function>writeq</function>.
+      </para>
+
+      <para>
+	Some devices (such as framebuffers) would like to use larger
+	transfers than 8 bytes at a time.  For these devices, the
+	<function>memcpy_toio</function>, <function>memcpy_fromio</function>
+	and <function>memset_io</function> functions are provided.
+	Do not use memset or memcpy on IO addresses; they
+	are not guaranteed to copy data in order.
+      </para>
+
+      <para>
+	The read and write functions are defined to be ordered. That is the
+	compiler is not permitted to reorder the I/O sequence. When the 
+	ordering can be compiler optimised, you can use <function>
+	__readb</function> and friends to indicate the relaxed ordering. Use 
+	this with care.
+      </para>
+
+      <para>
+	While the basic functions are defined to be synchronous with respect
+	to each other and ordered with respect to each other the busses the
+	devices sit on may themselves have asynchronicity. In particular many
+	authors are burned by the fact that PCI bus writes are posted
+	asynchronously. A driver author must issue a read from the same
+	device to ensure that writes have occurred in the specific cases the
+	author cares. This kind of property cannot be hidden from driver
+	writers in the API.  In some cases, the read used to flush the device
+	may be expected to fail (if the card is resetting, for example).  In
+	that case, the read should be done from config space, which is
+	guaranteed to soft-fail if the card doesn't respond.
+      </para>
+
+      <para>
+	The following is an example of flushing a write to a device when
+	the driver would like to ensure the write's effects are visible prior
+	to continuing execution.
+      </para>
+
+<programlisting>
+static inline void
+qla1280_disable_intrs(struct scsi_qla_host *ha)
+{
+	struct device_reg *reg;
+
+	reg = ha->iobase;
+	/* disable risc and host interrupts */
+	WRT_REG_WORD(&amp;reg->ictrl, 0);
+	/*
+	 * The following read will ensure that the above write
+	 * has been received by the device before we return from this
+	 * function.
+	 */
+	RD_REG_WORD(&amp;reg->ictrl);
+	ha->flags.ints_enabled = 0;
+}
+</programlisting>
+
+      <para>
+	In addition to write posting, on some large multiprocessing systems
+	(e.g. SGI Challenge, Origin and Altix machines) posted writes won't
+	be strongly ordered coming from different CPUs.  Thus it's important
+	to properly protect parts of your driver that do memory-mapped writes
+	with locks and use the <function>mmiowb</function> to make sure they
+	arrive in the order intended.  Issuing a regular <function>readX
+	</function> will also ensure write ordering, but should only be used
+	when the driver has to be sure that the write has actually arrived
+	at the device (not that it's simply ordered with respect to other
+	writes), since a full <function>readX</function> is a relatively
+	expensive operation.
+      </para>
+
+      <para>
+	Generally, one should use <function>mmiowb</function> prior to
+	releasing a spinlock that protects regions using <function>writeb
+	</function> or similar functions that aren't surrounded by <function>
+	readb</function> calls, which will ensure ordering and flushing.  The
+	following pseudocode illustrates what might occur if write ordering
+	isn't guaranteed via <function>mmiowb</function> or one of the
+	<function>readX</function> functions.
+      </para>
+
+<programlisting>
+CPU A:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU A:  ...
+CPU A:  writel(newval, ring_ptr);
+CPU A:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+        ...
+CPU B:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU B:  writel(newval2, ring_ptr);
+CPU B:  ...
+CPU B:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+</programlisting>
+
+      <para>
+	In the case above, newval2 could be written to ring_ptr before
+	newval.  Fixing it is easy though:
+      </para>
+
+<programlisting>
+CPU A:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU A:  ...
+CPU A:  writel(newval, ring_ptr);
+CPU A:  mmiowb(); /* ensure no other writes beat us to the device */
+CPU A:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+        ...
+CPU B:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU B:  writel(newval2, ring_ptr);
+CPU B:  ...
+CPU B:  mmiowb();
+CPU B:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+</programlisting>
+
+      <para>
+	See tg3.c for a real world example of how to use <function>mmiowb
+	</function>
+      </para>
+
+      <para>
+	PCI ordering rules also guarantee that PIO read responses arrive
+	after any outstanding DMA writes from that bus, since for some devices
+	the result of a <function>readb</function> call may signal to the
+	driver that a DMA transaction is complete.  In many cases, however,
+	the driver may want to indicate that the next
+	<function>readb</function> call has no relation to any previous DMA
+	writes performed by the device.  The driver can use
+	<function>readb_relaxed</function> for these cases, although only
+	some platforms will honor the relaxed semantics.  Using the relaxed
+	read functions will provide significant performance benefits on
+	platforms that support it.  The qla2xxx driver provides examples
+	of how to use <function>readX_relaxed</function>.  In many cases,
+	a majority of the driver's <function>readX</function> calls can
+	safely be converted to <function>readX_relaxed</function> calls, since
+	only a few will indicate or depend on DMA completion.
+      </para>
+    </sect1>
+
+    <sect1>
+      <title>ISA legacy functions</title>
+      <para>
+	On older kernels (2.2 and earlier) the ISA bus could be read or
+	written with these functions and without ioremap being used. This is
+	no longer true in Linux 2.4. A set of equivalent functions exist for
+	easy legacy driver porting. The functions available are prefixed
+	with 'isa_' and are <function>isa_readb</function>,
+	<function>isa_writeb</function>, <function>isa_readw</function>, 
+	<function>isa_writew</function>, <function>isa_readl</function>,
+	<function>isa_writel</function>, <function>isa_memcpy_fromio</function>
+	and <function>isa_memcpy_toio</function>
+      </para>
+      <para>
+	These functions should not be used in new drivers, and will
+	eventually be going away.
+      </para>
+    </sect1>
+
+  </chapter>
+
+  <chapter>
+    <title>Port Space Accesses</title>
+    <sect1>
+      <title>Port Space Explained</title>
+
+      <para>
+	Another form of IO commonly supported is Port Space.  This is a
+	range of addresses separate to the normal memory address space.
+	Access to these addresses is generally not as fast as accesses
+	to the memory mapped addresses, and it also has a potentially
+	smaller address space.
+      </para>
+
+      <para>
+	Unlike memory mapped IO, no preparation is required
+	to access port space.
+      </para>
+
+    </sect1>
+    <sect1>
+      <title>Accessing Port Space</title>
+      <para>
+	Accesses to this space are provided through a set of functions
+	which allow 8-bit, 16-bit and 32-bit accesses; also
+	known as byte, word and long.  These functions are
+	<function>inb</function>, <function>inw</function>,
+	<function>inl</function>, <function>outb</function>,
+	<function>outw</function> and <function>outl</function>.
+      </para>
+
+      <para>
+	Some variants are provided for these functions.  Some devices
+	require that accesses to their ports are slowed down.  This
+	functionality is provided by appending a <function>_p</function>
+	to the end of the function.  There are also equivalents to memcpy.
+	The <function>ins</function> and <function>outs</function>
+	functions copy bytes, words or longs to the given port.
+      </para>
+    </sect1>
+
+  </chapter>
+
+  <chapter id="pubfunctions">
+     <title>Public Functions Provided</title>
+!Einclude/asm-i386/io.h
+  </chapter>
+
+</book>
diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl
new file mode 100644
index 000000000000..a34442436128
--- /dev/null
+++ b/Documentation/DocBook/gadget.tmpl
@@ -0,0 +1,752 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="USB-Gadget-API">
+  <bookinfo>
+    <title>USB Gadget API for Linux</title>
+    <date>20 August 2004</date>
+    <edition>20 August 2004</edition>
+  
+    <legalnotice>
+       <para>
+	 This documentation is free software; you can redistribute
+	 it and/or modify it under the terms of the GNU General Public
+	 License as published by the Free Software Foundation; either
+	 version 2 of the License, or (at your option) any later
+	 version.
+       </para>
+	  
+       <para>
+	 This program is distributed in the hope that it will be
+	 useful, but WITHOUT ANY WARRANTY; without even the implied
+	 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+	 See the GNU General Public License for more details.
+       </para>
+	  
+       <para>
+	 You should have received a copy of the GNU General Public
+	 License along with this program; if not, write to the Free
+	 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+	 MA 02111-1307 USA
+       </para>
+	  
+       <para>
+	 For more details see the file COPYING in the source
+	 distribution of Linux.
+       </para>
+    </legalnotice>
+    <copyright>
+      <year>2003-2004</year>
+      <holder>David Brownell</holder>
+    </copyright>
+
+    <author>
+      <firstname>David</firstname> 
+      <surname>Brownell</surname>
+      <affiliation>
+        <address><email>dbrownell@users.sourceforge.net</email></address>
+      </affiliation>
+    </author>
+  </bookinfo>
+
+<toc></toc>
+
+<chapter><title>Introduction</title>
+
+<para>This document presents a Linux-USB "Gadget"
+kernel mode
+API, for use within peripherals and other USB devices
+that embed Linux.
+It provides an overview of the API structure,
+and shows how that fits into a system development project.
+This is the first such API released on Linux to address
+a number of important problems, including: </para>
+
+<itemizedlist>
+    <listitem><para>Supports USB 2.0, for high speed devices which
+	can stream data at several dozen megabytes per second.
+	</para></listitem>
+    <listitem><para>Handles devices with dozens of endpoints just as
+	well as ones with just two fixed-function ones.  Gadget drivers
+	can be written so they're easy to port to new hardware.
+	</para></listitem>
+    <listitem><para>Flexible enough to expose more complex USB device
+	capabilities such as multiple configurations, multiple interfaces,
+	composite devices,
+	and alternate interface settings.
+	</para></listitem>
+    <listitem><para>USB "On-The-Go" (OTG) support, in conjunction
+	with updates to the Linux-USB host side.
+	</para></listitem>
+    <listitem><para>Sharing data structures and API models with the
+	Linux-USB host side API.  This helps the OTG support, and
+	looks forward to more-symmetric frameworks (where the same
+	I/O model is used by both host and device side drivers).
+	</para></listitem>
+    <listitem><para>Minimalist, so it's easier to support new device
+	controller hardware.  I/O processing doesn't imply large
+	demands for memory or CPU resources.
+	</para></listitem>
+</itemizedlist>
+
+
+<para>Most Linux developers will not be able to use this API, since they
+have USB "host" hardware in a PC, workstation, or server.
+Linux users with embedded systems are more likely to
+have USB peripheral hardware.
+To distinguish drivers running inside such hardware from the
+more familiar Linux "USB device drivers",
+which are host side proxies for the real USB devices,
+a different term is used:
+the drivers inside the peripherals are "USB gadget drivers".
+In USB protocol interactions, the device driver is the master
+(or "client driver")
+and the gadget driver is the slave (or "function driver").
+</para>
+
+<para>The gadget API resembles the host side Linux-USB API in that both
+use queues of request objects to package I/O buffers, and those requests
+may be submitted or canceled.
+They share common definitions for the standard USB
+<emphasis>Chapter 9</emphasis> messages, structures, and constants.
+Also, both APIs bind and unbind drivers to devices.
+The APIs differ in detail, since the host side's current
+URB framework exposes a number of implementation details
+and assumptions that are inappropriate for a gadget API.
+While the model for control transfers and configuration
+management is necessarily different (one side is a hardware-neutral master,
+the other is a hardware-aware slave), the endpoint I/0 API used here
+should also be usable for an overhead-reduced host side API.
+</para>
+
+</chapter>
+
+<chapter id="structure"><title>Structure of Gadget Drivers</title>
+
+<para>A system running inside a USB peripheral
+normally has at least three layers inside the kernel to handle
+USB protocol processing, and may have additional layers in
+user space code.
+The "gadget" API is used by the middle layer to interact
+with the lowest level (which directly handles hardware).
+</para>
+
+<para>In Linux, from the bottom up, these layers are:
+</para>
+
+<variablelist>
+
+    <varlistentry>
+        <term><emphasis>USB Controller Driver</emphasis></term>
+
+	<listitem>
+	<para>This is the lowest software level.
+	It is the only layer that talks to hardware,
+	through registers, fifos, dma, irqs, and the like.
+	The <filename>&lt;linux/usb_gadget.h&gt;</filename> API abstracts
+	the peripheral controller endpoint hardware.
+	That hardware is exposed through endpoint objects, which accept
+	streams of IN/OUT buffers, and through callbacks that interact
+	with gadget drivers.
+	Since normal USB devices only have one upstream
+	port, they only have one of these drivers.
+	The controller driver can support any number of different
+	gadget drivers, but only one of them can be used at a time.
+	</para>
+
+	<para>Examples of such controller hardware include
+	the PCI-based NetChip 2280 USB 2.0 high speed controller,
+	the SA-11x0 or PXA-25x UDC (found within many PDAs),
+	and a variety of other products.
+	</para>
+
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term><emphasis>Gadget Driver</emphasis></term>
+
+	<listitem>
+	<para>The lower boundary of this driver implements hardware-neutral
+	USB functions, using calls to the controller driver.
+	Because such hardware varies widely in capabilities and restrictions,
+	and is used in embedded environments where space is at a premium,
+	the gadget driver is often configured at compile time
+	to work with endpoints supported by one particular controller.
+	Gadget drivers may be portable to several different controllers,
+	using conditional compilation.
+	(Recent kernels substantially simplify the work involved in
+	supporting new hardware, by <emphasis>autoconfiguring</emphasis>
+	endpoints automatically for many bulk-oriented drivers.)
+	Gadget driver responsibilities include:
+	</para>
+	<itemizedlist>
+	    <listitem><para>handling setup requests (ep0 protocol responses)
+		possibly including class-specific functionality
+		</para></listitem>
+	    <listitem><para>returning configuration and string descriptors
+		</para></listitem>
+	    <listitem><para>(re)setting configurations and interface
+		altsettings, including enabling and configuring endpoints
+		</para></listitem>
+	    <listitem><para>handling life cycle events, such as managing
+		bindings to hardware,
+		USB suspend/resume, remote wakeup,
+		and disconnection from the USB host.
+		</para></listitem>
+	    <listitem><para>managing IN and OUT transfers on all currently
+		enabled endpoints
+		</para></listitem>
+	</itemizedlist>
+
+	<para>
+	Such drivers may be modules of proprietary code, although
+	that approach is discouraged in the Linux community.
+	</para>
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term><emphasis>Upper Level</emphasis></term>
+
+	<listitem>
+	<para>Most gadget drivers have an upper boundary that connects
+	to some Linux driver or framework in Linux.
+	Through that boundary flows the data which the gadget driver
+	produces and/or consumes through protocol transfers over USB.
+	Examples include:
+	</para>
+	<itemizedlist>
+	    <listitem><para>user mode code, using generic (gadgetfs)
+	        or application specific files in
+		<filename>/dev</filename>
+		</para></listitem>
+	    <listitem><para>networking subsystem (for network gadgets,
+		like the CDC Ethernet Model gadget driver)
+		</para></listitem>
+	    <listitem><para>data capture drivers, perhaps video4Linux or
+		 a scanner driver; or test and measurement hardware.
+		 </para></listitem>
+	    <listitem><para>input subsystem (for HID gadgets)
+		</para></listitem>
+	    <listitem><para>sound subsystem (for audio gadgets)
+		</para></listitem>
+	    <listitem><para>file system (for PTP gadgets)
+		</para></listitem>
+	    <listitem><para>block i/o subsystem (for usb-storage gadgets)
+		</para></listitem>
+	    <listitem><para>... and more </para></listitem>
+	</itemizedlist>
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term><emphasis>Additional Layers</emphasis></term>
+
+	<listitem>
+	<para>Other layers may exist.
+	These could include kernel layers, such as network protocol stacks,
+	as well as user mode applications building on standard POSIX
+	system call APIs such as
+	<emphasis>open()</emphasis>, <emphasis>close()</emphasis>,
+	<emphasis>read()</emphasis> and <emphasis>write()</emphasis>.
+	On newer systems, POSIX Async I/O calls may be an option.
+	Such user mode code will not necessarily be subject to
+	the GNU General Public License (GPL).
+	</para>
+	</listitem></varlistentry>
+
+
+</variablelist>
+
+<para>OTG-capable systems will also need to include a standard Linux-USB
+host side stack,
+with <emphasis>usbcore</emphasis>,
+one or more <emphasis>Host Controller Drivers</emphasis> (HCDs),
+<emphasis>USB Device Drivers</emphasis> to support
+the OTG "Targeted Peripheral List",
+and so forth.
+There will also be an <emphasis>OTG Controller Driver</emphasis>,
+which is visible to gadget and device driver developers only indirectly.
+That helps the host and device side USB controllers implement the
+two new OTG protocols (HNP and SRP).
+Roles switch (host to peripheral, or vice versa) using HNP
+during USB suspend processing, and SRP can be viewed as a
+more battery-friendly kind of device wakeup protocol.
+</para>
+
+<para>Over time, reusable utilities are evolving to help make some
+gadget driver tasks simpler.
+For example, building configuration descriptors from vectors of
+descriptors for the configurations interfaces and endpoints is
+now automated, and many drivers now use autoconfiguration to
+choose hardware endpoints and initialize their descriptors.
+
+A potential example of particular interest
+is code implementing standard USB-IF protocols for
+HID, networking, storage, or audio classes.
+Some developers are interested in KDB or KGDB hooks, to let
+target hardware be remotely debugged.
+Most such USB protocol code doesn't need to be hardware-specific,
+any more than network protocols like X11, HTTP, or NFS are.
+Such gadget-side interface drivers should eventually be combined,
+to implement composite devices.
+</para>
+
+</chapter>
+
+
+<chapter id="api"><title>Kernel Mode Gadget API</title>
+
+<para>Gadget drivers declare themselves through a
+<emphasis>struct usb_gadget_driver</emphasis>, which is responsible for
+most parts of enumeration for a <emphasis>struct usb_gadget</emphasis>.
+The response to a set_configuration usually involves
+enabling one or more of the <emphasis>struct usb_ep</emphasis> objects
+exposed by the gadget, and submitting one or more
+<emphasis>struct usb_request</emphasis> buffers to transfer data.
+Understand those four data types, and their operations, and
+you will understand how this API works.
+</para> 
+
+<note><title>Incomplete Data Type Descriptions</title>
+
+<para>This documentation was prepared using the standard Linux
+kernel <filename>docproc</filename> tool, which turns text
+and in-code comments into SGML DocBook and then into usable
+formats such as HTML or PDF.
+Other than the "Chapter 9" data types, most of the significant
+data types and functions are described here.
+</para>
+
+<para>However, docproc does not understand all the C constructs
+that are used, so some relevant information is likely omitted from
+what you are reading.  
+One example of such information is endpoint autoconfiguration.
+You'll have to read the header file, and use example source
+code (such as that for "Gadget Zero"), to fully understand the API.
+</para>
+
+<para>The part of the API implementing some basic
+driver capabilities is specific to the version of the
+Linux kernel that's in use.
+The 2.6 kernel includes a <emphasis>driver model</emphasis>
+framework that has no analogue on earlier kernels;
+so those parts of the gadget API are not fully portable.
+(They are implemented on 2.4 kernels, but in a different way.)
+The driver model state is another part of this API that is
+ignored by the kerneldoc tools.
+</para>
+</note>
+
+<para>The core API does not expose
+every possible hardware feature, only the most widely available ones.
+There are significant hardware features, such as device-to-device DMA
+(without temporary storage in a memory buffer)
+that would be added using hardware-specific APIs.
+</para>
+
+<para>This API allows drivers to use conditional compilation to handle
+endpoint capabilities of different hardware, but doesn't require that.
+Hardware tends to have arbitrary restrictions, relating to
+transfer types, addressing, packet sizes, buffering, and availability.
+As a rule, such differences only matter for "endpoint zero" logic
+that handles device configuration and management.
+The API supports limited run-time
+detection of capabilities, through naming conventions for endpoints.
+Many drivers will be able to at least partially autoconfigure
+themselves.
+In particular, driver init sections will often have endpoint
+autoconfiguration logic that scans the hardware's list of endpoints
+to find ones matching the driver requirements
+(relying on those conventions), to eliminate some of the most
+common reasons for conditional compilation.
+</para>
+
+<para>Like the Linux-USB host side API, this API exposes
+the "chunky" nature of USB messages:  I/O requests are in terms
+of one or more "packets", and packet boundaries are visible to drivers.
+Compared to RS-232 serial protocols, USB resembles
+synchronous protocols like HDLC
+(N bytes per frame, multipoint addressing, host as the primary
+station and devices as secondary stations)
+more than asynchronous ones
+(tty style:  8 data bits per frame, no parity, one stop bit).
+So for example the controller drivers won't buffer
+two single byte writes into a single two-byte USB IN packet,
+although gadget drivers may do so when they implement
+protocols where packet boundaries (and "short packets")
+are not significant.
+</para>
+
+<sect1 id="lifecycle"><title>Driver Life Cycle</title>
+
+<para>Gadget drivers make endpoint I/O requests to hardware without
+needing to know many details of the hardware, but driver
+setup/configuration code needs to handle some differences.
+Use the API like this:
+</para>
+
+<orderedlist numeration='arabic'>
+
+<listitem><para>Register a driver for the particular device side
+usb controller hardware,
+such as the net2280 on PCI (USB 2.0),
+sa11x0 or pxa25x as found in Linux PDAs,
+and so on.
+At this point the device is logically in the USB ch9 initial state
+("attached"), drawing no power and not usable
+(since it does not yet support enumeration).
+Any host should not see the device, since it's not
+activated the data line pullup used by the host to
+detect a device, even if VBUS power is available.
+</para></listitem>
+
+<listitem><para>Register a gadget driver that implements some higher level
+device function.  That will then bind() to a usb_gadget, which
+activates the data line pullup sometime after detecting VBUS.
+</para></listitem>
+
+<listitem><para>The hardware driver can now start enumerating.
+The steps it handles are to accept USB power and set_address requests.
+Other steps are handled by the gadget driver.
+If the gadget driver module is unloaded before the host starts to
+enumerate, steps before step 7 are skipped.
+</para></listitem>
+
+<listitem><para>The gadget driver's setup() call returns usb descriptors,
+based both on what the bus interface hardware provides and on the
+functionality being implemented.
+That can involve alternate settings or configurations,
+unless the hardware prevents such operation.
+For OTG devices, each configuration descriptor includes
+an OTG descriptor.
+</para></listitem>
+
+<listitem><para>The gadget driver handles the last step of enumeration,
+when the USB host issues a set_configuration call.
+It enables all endpoints used in that configuration,
+with all interfaces in their default settings.
+That involves using a list of the hardware's endpoints, enabling each
+endpoint according to its descriptor.
+It may also involve using <function>usb_gadget_vbus_draw</function>
+to let more power be drawn from VBUS, as allowed by that configuration.
+For OTG devices, setting a configuration may also involve reporting
+HNP capabilities through a user interface.
+</para></listitem>
+
+<listitem><para>Do real work and perform data transfers, possibly involving
+changes to interface settings or switching to new configurations, until the
+device is disconnect()ed from the host.
+Queue any number of transfer requests to each endpoint.
+It may be suspended and resumed several times before being disconnected.
+On disconnect, the drivers go back to step 3 (above).
+</para></listitem>
+
+<listitem><para>When the gadget driver module is being unloaded,
+the driver unbind() callback is issued.  That lets the controller
+driver be unloaded.
+</para></listitem>
+
+</orderedlist>
+
+<para>Drivers will normally be arranged so that just loading the
+gadget driver module (or statically linking it into a Linux kernel)
+allows the peripheral device to be enumerated, but some drivers
+will defer enumeration until some higher level component (like
+a user mode daemon) enables it.
+Note that at this lowest level there are no policies about how
+ep0 configuration logic is implemented,
+except that it should obey USB specifications.
+Such issues are in the domain of gadget drivers,
+including knowing about implementation constraints
+imposed by some USB controllers
+or understanding that composite devices might happen to
+be built by integrating reusable components.
+</para>
+
+<para>Note that the lifecycle above can be slightly different
+for OTG devices.
+Other than providing an additional OTG descriptor in each
+configuration, only the HNP-related differences are particularly
+visible to driver code.
+They involve reporting requirements during the SET_CONFIGURATION
+request, and the option to invoke HNP during some suspend callbacks.
+Also, SRP changes the semantics of
+<function>usb_gadget_wakeup</function>
+slightly.
+</para>
+
+</sect1>
+
+<sect1 id="ch9"><title>USB 2.0 Chapter 9 Types and Constants</title>
+
+<para>Gadget drivers
+rely on common USB structures and constants
+defined in the
+<filename>&lt;linux/usb_ch9.h&gt;</filename>
+header file, which is standard in Linux 2.6 kernels.
+These are the same types and constants used by host
+side drivers (and usbcore).
+</para>
+
+!Iinclude/linux/usb_ch9.h
+</sect1>
+
+<sect1 id="core"><title>Core Objects and Methods</title>
+
+<para>These are declared in
+<filename>&lt;linux/usb_gadget.h&gt;</filename>,
+and are used by gadget drivers to interact with
+USB peripheral controller drivers.
+</para>
+
+	<!-- yeech, this is ugly in nsgmls PDF output.
+
+	     the PDF bookmark and refentry output nesting is wrong,
+	     and the member/argument documentation indents ugly.
+
+	     plus something (docproc?) adds whitespace before the
+	     descriptive paragraph text, so it can't line up right
+	     unless the explanations are trivial.
+	  -->
+
+!Iinclude/linux/usb_gadget.h
+</sect1>
+
+<sect1 id="utils"><title>Optional Utilities</title>
+
+<para>The core API is sufficient for writing a USB Gadget Driver,
+but some optional utilities are provided to simplify common tasks.
+These utilities include endpoint autoconfiguration.
+</para>
+
+!Edrivers/usb/gadget/usbstring.c
+!Edrivers/usb/gadget/config.c
+<!-- !Edrivers/usb/gadget/epautoconf.c -->
+</sect1>
+
+</chapter>
+
+<chapter id="controllers"><title>Peripheral Controller Drivers</title>
+
+<para>The first hardware supporting this API was the NetChip 2280
+controller, which supports USB 2.0 high speed and is based on PCI.
+This is the <filename>net2280</filename> driver module.
+The driver supports Linux kernel versions 2.4 and 2.6;
+contact NetChip Technologies for development boards and product
+information.
+</para> 
+
+<para>Other hardware working in the "gadget" framework includes:
+Intel's PXA 25x and IXP42x series processors
+(<filename>pxa2xx_udc</filename>),
+Toshiba TC86c001 "Goku-S" (<filename>goku_udc</filename>),
+Renesas SH7705/7727 (<filename>sh_udc</filename>),
+MediaQ 11xx (<filename>mq11xx_udc</filename>),
+Hynix HMS30C7202 (<filename>h7202_udc</filename>),
+National 9303/4 (<filename>n9604_udc</filename>),
+Texas Instruments OMAP (<filename>omap_udc</filename>),
+Sharp LH7A40x (<filename>lh7a40x_udc</filename>),
+and more.
+Most of those are full speed controllers.
+</para>
+
+<para>At this writing, there are people at work on drivers in
+this framework for several other USB device controllers,
+with plans to make many of them be widely available.
+</para>
+
+<!-- !Edrivers/usb/gadget/net2280.c -->
+
+<para>A partial USB simulator,
+the <filename>dummy_hcd</filename> driver, is available.
+It can act like a net2280, a pxa25x, or an sa11x0 in terms
+of available endpoints and device speeds; and it simulates
+control, bulk, and to some extent interrupt transfers.
+That lets you develop some parts of a gadget driver on a normal PC,
+without any special hardware, and perhaps with the assistance
+of tools such as GDB running with User Mode Linux.
+At least one person has expressed interest in adapting that
+approach, hooking it up to a simulator for a microcontroller.
+Such simulators can help debug subsystems where the runtime hardware
+is unfriendly to software development, or is not yet available.
+</para>
+
+<para>Support for other controllers is expected to be developed
+and contributed
+over time, as this driver framework evolves.
+</para>
+
+</chapter>
+
+<chapter id="gadget"><title>Gadget Drivers</title>
+
+<para>In addition to <emphasis>Gadget Zero</emphasis>
+(used primarily for testing and development with drivers
+for usb controller hardware), other gadget drivers exist.
+</para>
+
+<para>There's an <emphasis>ethernet</emphasis> gadget
+driver, which implements one of the most useful
+<emphasis>Communications Device Class</emphasis> (CDC) models.  
+One of the standards for cable modem interoperability even
+specifies the use of this ethernet model as one of two
+mandatory options.
+Gadgets using this code look to a USB host as if they're
+an Ethernet adapter.
+It provides access to a network where the gadget's CPU is one host,
+which could easily be bridging, routing, or firewalling
+access to other networks.
+Since some hardware can't fully implement the CDC Ethernet
+requirements, this driver also implements a "good parts only"
+subset of CDC Ethernet.
+(That subset doesn't advertise itself as CDC Ethernet,
+to avoid creating problems.)
+</para>
+
+<para>Support for Microsoft's <emphasis>RNDIS</emphasis>
+protocol has been contributed by Pengutronix and Auerswald GmbH.
+This is like CDC Ethernet, but it runs on more slightly USB hardware
+(but less than the CDC subset).
+However, its main claim to fame is being able to connect directly to
+recent versions of Windows, using drivers that Microsoft bundles
+and supports, making it much simpler to network with Windows.
+</para>
+
+<para>There is also support for user mode gadget drivers,
+using <emphasis>gadgetfs</emphasis>.
+This provides a <emphasis>User Mode API</emphasis> that presents
+each endpoint as a single file descriptor.  I/O is done using
+normal <emphasis>read()</emphasis> and <emphasis>read()</emphasis> calls.
+Familiar tools like GDB and pthreads can be used to
+develop and debug user mode drivers, so that once a robust
+controller driver is available many applications for it
+won't require new kernel mode software.
+Linux 2.6 <emphasis>Async I/O (AIO)</emphasis>
+support is available, so that user mode software
+can stream data with only slightly more overhead
+than a kernel driver.
+</para>
+
+<para>There's a USB Mass Storage class driver, which provides
+a different solution for interoperability with systems such
+as MS-Windows and MacOS.
+That <emphasis>File-backed Storage</emphasis> driver uses a
+file or block device as backing store for a drive,
+like the <filename>loop</filename> driver.
+The USB host uses the BBB, CB, or CBI versions of the mass
+storage class specification, using transparent SCSI commands
+to access the data from the backing store.
+</para>
+
+<para>There's a "serial line" driver, useful for TTY style
+operation over USB.
+The latest version of that driver supports CDC ACM style
+operation, like a USB modem, and so on most hardware it can
+interoperate easily with MS-Windows.
+One interesting use of that driver is in boot firmware (like a BIOS),
+which can sometimes use that model with very small systems without
+real serial lines.
+</para>
+
+<para>Support for other kinds of gadget is expected to
+be developed and contributed
+over time, as this driver framework evolves.
+</para>
+
+</chapter>
+
+<chapter id="otg"><title>USB On-The-GO (OTG)</title>
+
+<para>USB OTG support on Linux 2.6 was initially developed
+by Texas Instruments for
+<ulink url="http://www.omap.com">OMAP</ulink> 16xx and 17xx
+series processors.
+Other OTG systems should work in similar ways, but the
+hardware level details could be very different.
+</para> 
+
+<para>Systems need specialized hardware support to implement OTG,
+notably including a special <emphasis>Mini-AB</emphasis> jack
+and associated transciever to support <emphasis>Dual-Role</emphasis>
+operation:
+they can act either as a host, using the standard
+Linux-USB host side driver stack,
+or as a peripheral, using this "gadget" framework.
+To do that, the system software relies on small additions
+to those programming interfaces,
+and on a new internal component (here called an "OTG Controller")
+affecting which driver stack connects to the OTG port.
+In each role, the system can re-use the existing pool of
+hardware-neutral drivers, layered on top of the controller
+driver interfaces (<emphasis>usb_bus</emphasis> or
+<emphasis>usb_gadget</emphasis>).
+Such drivers need at most minor changes, and most of the calls
+added to support OTG can also benefit non-OTG products.
+</para>
+
+<itemizedlist>
+    <listitem><para>Gadget drivers test the <emphasis>is_otg</emphasis>
+	flag, and use it to determine whether or not to include
+	an OTG descriptor in each of their configurations.
+	</para></listitem>
+    <listitem><para>Gadget drivers may need changes to support the
+	two new OTG protocols, exposed in new gadget attributes
+	such as <emphasis>b_hnp_enable</emphasis> flag.
+	HNP support should be reported through a user interface
+	(two LEDs could suffice), and is triggered in some cases
+	when the host suspends the peripheral.
+	SRP support can be user-initiated just like remote wakeup,
+	probably by pressing the same button.
+	</para></listitem>
+    <listitem><para>On the host side, USB device drivers need
+	to be taught to trigger HNP at appropriate moments, using
+	<function>usb_suspend_device()</function>.
+	That also conserves battery power, which is useful even
+	for non-OTG configurations.
+	</para></listitem>
+    <listitem><para>Also on the host side, a driver must support the
+	OTG "Targeted Peripheral List".  That's just a whitelist,
+	used to reject peripherals not supported with a given
+	Linux OTG host.
+	<emphasis>This whitelist is product-specific;
+	each product must modify <filename>otg_whitelist.h</filename>
+	to match its interoperability specification.
+	</emphasis>
+	</para>
+	<para>Non-OTG Linux hosts, like PCs and workstations,
+	normally have some solution for adding drivers, so that
+	peripherals that aren't recognized can eventually be supported.
+	That approach is unreasonable for consumer products that may
+	never have their firmware upgraded, and where it's usually
+	unrealistic to expect traditional PC/workstation/server kinds
+	of support model to work.
+	For example, it's often impractical to change device firmware
+	once the product has been distributed, so driver bugs can't
+	normally be fixed if they're found after shipment.
+	</para></listitem>
+</itemizedlist>
+
+<para>
+Additional changes are needed below those hardware-neutral
+<emphasis>usb_bus</emphasis> and <emphasis>usb_gadget</emphasis>
+driver interfaces; those aren't discussed here in any detail.
+Those affect the hardware-specific code for each USB Host or Peripheral
+controller, and how the HCD initializes (since OTG can be active only
+on a single port).
+They also involve what may be called an <emphasis>OTG Controller
+Driver</emphasis>, managing the OTG transceiver and the OTG state
+machine logic as well as much of the root hub behavior for the
+OTG port.
+The OTG controller driver needs to activate and deactivate USB
+controllers depending on the relevant device role.
+Some related changes were needed inside usbcore, so that it
+can identify OTG-capable devices and respond appropriately
+to HNP or SRP protocols.
+</para> 
+
+</chapter>
+
+</book>
+<!--
+	vim:syntax=sgml:sw=4
+-->
diff --git a/Documentation/DocBook/journal-api.tmpl b/Documentation/DocBook/journal-api.tmpl
new file mode 100644
index 000000000000..1ef6f43c6d8f
--- /dev/null
+++ b/Documentation/DocBook/journal-api.tmpl
@@ -0,0 +1,333 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="LinuxJBDAPI">
+ <bookinfo>
+  <title>The Linux Journalling API</title>
+  <authorgroup>
+  <author>
+     <firstname>Roger</firstname>
+     <surname>Gammans</surname>
+     <affiliation>
+     <address>
+      <email>rgammans@computer-surgery.co.uk</email>
+     </address>
+    </affiliation>
+     </author> 
+  </authorgroup>
+  
+  <authorgroup>
+   <author>
+    <firstname>Stephen</firstname>
+    <surname>Tweedie</surname>
+    <affiliation>
+     <address>
+      <email>sct@redhat.com</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2002</year>
+   <holder>Roger Gammans</holder>
+  </copyright>
+
+<legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="Overview">
+     <title>Overview</title>
+  <sect1>
+     <title>Details</title>
+<para>
+The journalling layer is  easy to use. You need to 
+first of all create a journal_t data structure. There are
+two calls to do this dependent on how you decide to allocate the physical
+media on which the journal resides. The journal_init_inode() call 
+is for journals stored in filesystem inodes, or the journal_init_dev()
+call can be use for journal stored on a raw device (in a continuous range 
+of blocks). A journal_t is a typedef for a struct pointer, so when
+you are finally finished make sure you call journal_destroy() on it
+to free up any used kernel memory.
+</para>
+
+<para>
+Once you have got your journal_t object you need to 'mount' or load the journal
+file, unless of course you haven't initialised it yet - in which case you
+need to call journal_create().
+</para>
+
+<para>
+Most of the time however your journal file will already have been created, but
+before you load it you must call journal_wipe() to empty the journal file.
+Hang on, you say , what if the filesystem wasn't cleanly umount()'d . Well, it is the 
+job of the client file system to detect this and skip the call to journal_wipe().
+</para>
+
+<para>
+In either case the next call should be to journal_load() which prepares the
+journal file for use. Note that journal_wipe(..,0) calls journal_skip_recovery() 
+for you if it detects any outstanding transactions in the journal and similarly
+journal_load() will call journal_recover() if necessary.
+I would advise reading fs/ext3/super.c for examples on this stage.
+[RGG: Why is the journal_wipe() call necessary - doesn't this needlessly 
+complicate the API. Or isn't a good idea for the journal layer to hide 
+dirty mounts from the client fs]
+</para>
+
+<para>
+Now you can go ahead and start modifying the underlying 
+filesystem. Almost.
+</para>
+
+
+<para>
+
+You still need to actually journal your filesystem changes, this
+is done by wrapping them into transactions. Additionally you
+also need to wrap the modification of each of the the buffers
+with calls to the journal layer, so it knows what the modifications
+you are actually making are. To do this use  journal_start() which
+returns a transaction handle.
+</para>
+
+<para>
+journal_start()
+and its counterpart journal_stop(), which indicates the end of a transaction
+are nestable calls, so you can reenter a transaction if necessary,
+but remember you must call journal_stop() the same number of times as
+journal_start() before the transaction is completed (or more accurately
+leaves the the update phase). Ext3/VFS makes use of this feature to simplify 
+quota support.
+</para>
+
+<para>
+Inside each transaction you need to wrap the modifications to the
+individual buffers (blocks). Before you start to modify a buffer you
+need to call journal_get_{create,write,undo}_access() as appropriate,
+this allows the journalling layer to copy the unmodified data if it
+needs to. After all the buffer may be part of a previously uncommitted
+transaction. 
+At this point you are at last ready to modify a buffer, and once
+you are have done so you need to call journal_dirty_{meta,}data().
+Or if you've asked for access to a buffer you now know is now longer 
+required to be pushed back on the device you can call journal_forget()
+in much the same way as you might have used bforget() in the past.
+</para>
+
+<para>
+A journal_flush() may be called at any time to commit and checkpoint
+all your transactions.
+</para>
+
+<para>
+Then at umount time , in your put_super() (2.4) or write_super() (2.5)
+you can then call journal_destroy() to clean up your in-core journal object.
+</para>
+
+
+<para>
+Unfortunately there a couple of ways the journal layer can cause a deadlock.
+The first thing to note is that each task can only have
+a single outstanding transaction at any one time, remember nothing
+commits until the outermost journal_stop(). This means
+you must complete the transaction at the end of each file/inode/address
+etc. operation you perform, so that the journalling system isn't re-entered
+on another journal. Since transactions can't be nested/batched 
+across differing journals, and another filesystem other than
+yours (say ext3) may be modified in a later syscall.
+</para>
+
+<para>
+The second case to bear in mind is that journal_start() can 
+block if there isn't enough space in the journal for your transaction 
+(based on the passed nblocks param) - when it blocks it merely(!) needs to
+wait for transactions to complete and be committed from other tasks, 
+so essentially we are waiting for journal_stop(). So to avoid 
+deadlocks you must treat journal_start/stop() as if they
+were semaphores and include them in your semaphore ordering rules to prevent 
+deadlocks. Note that journal_extend() has similar blocking behaviour to
+journal_start() so you can deadlock here just as easily as on journal_start().
+</para>
+
+<para>
+Try to reserve the right number of blocks the first time. ;-). This will
+be the maximum number of blocks you are going to touch in this transaction.
+I advise having a look at at least ext3_jbd.h to see the basis on which 
+ext3 uses to make these decisions.
+</para>
+
+<para>
+Another wriggle to watch out for is your on-disk block allocation strategy.
+why? Because, if you undo a delete, you need to ensure you haven't reused any
+of the freed blocks in a later transaction. One simple way of doing this
+is make sure any blocks you allocate only have checkpointed transactions
+listed against them. Ext3 does this in ext3_test_allocatable(). 
+</para>
+
+<para>
+Lock is also providing through journal_{un,}lock_updates(),
+ext3 uses this when it wants a window with a clean and stable fs for a moment.
+eg. 
+</para>
+
+<programlisting>
+
+	journal_lock_updates() //stop new stuff happening..
+	journal_flush()        // checkpoint everything.
+	..do stuff on stable fs
+	journal_unlock_updates() // carry on with filesystem use.
+</programlisting>
+
+<para>
+The opportunities for abuse and DOS attacks with this should be obvious,
+if you allow unprivileged userspace to trigger codepaths containing these
+calls.
+</para>
+
+<para>
+A new feature of jbd since 2.5.25 is commit callbacks with the new
+journal_callback_set() function you can now ask the journalling layer
+to call you back when the transaction is finally committed to disk, so that
+you can do some of your own management. The key to this is the journal_callback
+struct, this maintains the internal callback information but you can
+extend it like this:-
+</para>
+<programlisting>
+	struct  myfs_callback_s {
+		//Data structure element required by jbd..
+		struct journal_callback for_jbd;
+		// Stuff for myfs allocated together.
+		myfs_inode*    i_commited;
+	
+	}
+</programlisting>
+
+<para>
+this would be useful if you needed to know when data was committed to a 
+particular inode.
+</para>
+
+</sect1>
+
+<sect1>
+<title>Summary</title>
+<para>
+Using the journal is a matter of wrapping the different context changes,
+being each mount, each modification (transaction) and each changed buffer
+to tell the journalling layer about them.
+</para>
+
+<para>
+Here is a some pseudo code to give you an idea of how it works, as
+an example.
+</para>
+
+<programlisting>
+  journal_t* my_jnrl = journal_create();
+  journal_init_{dev,inode}(jnrl,...)
+  if (clean) journal_wipe();
+  journal_load();
+
+   foreach(transaction) { /*transactions must be 
+                            completed before
+                            a syscall returns to 
+                            userspace*/
+
+          handle_t * xct=journal_start(my_jnrl);
+          foreach(bh) {
+                journal_get_{create,write,undo}_access(xact,bh);
+                if ( myfs_modify(bh) ) { /* returns true 
+                                        if makes changes */
+                           journal_dirty_{meta,}data(xact,bh);
+                } else {
+                           journal_forget(bh);
+                }
+          }
+          journal_stop(xct);
+   }
+   journal_destroy(my_jrnl);
+</programlisting>
+</sect1>
+
+</chapter>
+
+  <chapter id="adt">
+     <title>Data Types</title>
+     <para>	
+	The journalling layer uses typedefs to 'hide' the concrete definitions
+	of the structures used. As a client of the JBD layer you can
+	just rely on the using the pointer as a magic cookie  of some sort.
+	
+	Obviously the hiding is not enforced as this is 'C'.
+	</para>
+	<sect1><title>Structures</title>
+!Iinclude/linux/jbd.h
+	</sect1>
+</chapter>
+
+  <chapter id="calls">
+     <title>Functions</title>
+     <para>	
+	The functions here are split into two groups those that
+	affect a journal as a whole, and those which are used to
+	manage transactions
+</para>
+	<sect1><title>Journal Level</title>
+!Efs/jbd/journal.c
+!Efs/jbd/recovery.c
+	</sect1>
+	<sect1><title>Transasction Level</title>
+!Efs/jbd/transaction.c	
+	</sect1>
+</chapter>
+<chapter>
+     <title>See also</title>
+	<para>
+	<citation>
+	   <ulink url="ftp://ftp.uk.linux.org/pub/linux/sct/fs/jfs/journal-design.ps.gz">
+	   	Journaling the Linux ext2fs Filesystem,LinuxExpo 98, Stephen Tweedie
+	   </ulink>
+	   </citation>
+	   </para>
+	   <para>
+	   <citation>
+	   <ulink url="http://olstrans.sourceforge.net/release/OLS2000-ext3/OLS2000-ext3.html">
+	   	Ext3 Journalling FileSystem , OLS 2000, Dr. Stephen Tweedie
+	   </ulink>
+	   </citation>
+	   </para>
+</chapter>
+
+</book>
diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl
new file mode 100644
index 000000000000..1bd20c860285
--- /dev/null
+++ b/Documentation/DocBook/kernel-api.tmpl
@@ -0,0 +1,342 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="LinuxKernelAPI">
+ <bookinfo>
+  <title>The Linux Kernel API</title>
+  
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="Basics">
+     <title>Driver Basics</title>
+     <sect1><title>Driver Entry and Exit points</title>
+!Iinclude/linux/init.h
+     </sect1>
+
+     <sect1><title>Atomic and pointer manipulation</title>
+!Iinclude/asm-i386/atomic.h
+!Iinclude/asm-i386/unaligned.h
+     </sect1>
+
+<!-- FIXME:
+  kernel/sched.c has no docs, which stuffs up the sgml.  Comment
+  out until somebody adds docs.  KAO
+     <sect1><title>Delaying, scheduling, and timer routines</title>
+X!Ekernel/sched.c
+     </sect1>
+KAO -->
+  </chapter>
+
+  <chapter id="adt">
+     <title>Data Types</title>
+     <sect1><title>Doubly Linked Lists</title>
+!Iinclude/linux/list.h
+     </sect1>
+  </chapter>
+
+  <chapter id="libc">
+     <title>Basic C Library Functions</title>
+
+     <para>
+       When writing drivers, you cannot in general use routines which are
+       from the C Library.  Some of the functions have been found generally
+       useful and they are listed below.  The behaviour of these functions
+       may vary slightly from those defined by ANSI, and these deviations
+       are noted in the text.
+     </para>
+
+     <sect1><title>String Conversions</title>
+!Ilib/vsprintf.c
+!Elib/vsprintf.c
+     </sect1>
+     <sect1><title>String Manipulation</title>
+!Ilib/string.c
+!Elib/string.c
+     </sect1>
+     <sect1><title>Bit Operations</title>
+!Iinclude/asm-i386/bitops.h
+     </sect1>
+  </chapter>
+
+  <chapter id="mm">
+     <title>Memory Management in Linux</title>
+     <sect1><title>The Slab Cache</title>
+!Emm/slab.c
+     </sect1>
+     <sect1><title>User Space Memory Access</title>
+!Iinclude/asm-i386/uaccess.h
+!Iarch/i386/lib/usercopy.c
+     </sect1>
+  </chapter>
+
+  <chapter id="kfifo">
+     <title>FIFO Buffer</title>
+     <sect1><title>kfifo interface</title>
+!Iinclude/linux/kfifo.h
+!Ekernel/kfifo.c
+     </sect1>
+  </chapter>
+
+  <chapter id="proc">
+     <title>The proc filesystem</title>
+ 
+     <sect1><title>sysctl interface</title>
+!Ekernel/sysctl.c
+     </sect1>
+  </chapter>
+
+  <chapter id="debugfs">
+     <title>The debugfs filesystem</title>
+ 
+     <sect1><title>debugfs interface</title>
+!Efs/debugfs/inode.c
+!Efs/debugfs/file.c
+     </sect1>
+  </chapter>
+
+  <chapter id="vfs">
+     <title>The Linux VFS</title>
+     <sect1><title>The Directory Cache</title>
+!Efs/dcache.c
+!Iinclude/linux/dcache.h
+     </sect1>
+     <sect1><title>Inode Handling</title>
+!Efs/inode.c
+!Efs/bad_inode.c
+     </sect1>
+     <sect1><title>Registration and Superblocks</title>
+!Efs/super.c
+     </sect1>
+     <sect1><title>File Locks</title>
+!Efs/locks.c
+!Ifs/locks.c
+     </sect1>
+  </chapter>
+
+  <chapter id="netcore">
+     <title>Linux Networking</title>
+     <sect1><title>Socket Buffer Functions</title>
+!Iinclude/linux/skbuff.h
+!Enet/core/skbuff.c
+     </sect1>
+     <sect1><title>Socket Filter</title>
+!Enet/core/filter.c
+     </sect1>
+     <sect1><title>Generic Network Statistics</title>
+!Iinclude/linux/gen_stats.h
+!Enet/core/gen_stats.c
+!Enet/core/gen_estimator.c
+     </sect1>
+  </chapter>
+
+  <chapter id="netdev">
+     <title>Network device support</title>
+     <sect1><title>Driver Support</title>
+!Enet/core/dev.c
+     </sect1>
+     <sect1><title>8390 Based Network Cards</title>
+!Edrivers/net/8390.c
+     </sect1>
+     <sect1><title>Synchronous PPP</title>
+!Edrivers/net/wan/syncppp.c
+     </sect1>
+  </chapter>
+
+  <chapter id="modload">
+     <title>Module Support</title>
+     <sect1><title>Module Loading</title>
+!Ekernel/kmod.c
+     </sect1>
+     <sect1><title>Inter Module support</title>
+        <para>
+           Refer to the file kernel/module.c for more information.
+        </para>
+<!-- FIXME: Removed for now since no structured comments in source
+X!Ekernel/module.c
+-->
+     </sect1>
+  </chapter>
+
+  <chapter id="hardware">
+     <title>Hardware Interfaces</title>
+     <sect1><title>Interrupt Handling</title>
+!Iarch/i386/kernel/irq.c
+     </sect1>
+
+     <sect1><title>MTRR Handling</title>
+!Earch/i386/kernel/cpu/mtrr/main.c
+     </sect1>
+     <sect1><title>PCI Support Library</title>
+!Edrivers/pci/pci.c
+     </sect1>
+     <sect1><title>PCI Hotplug Support Library</title>
+!Edrivers/pci/hotplug/pci_hotplug_core.c
+     </sect1>
+     <sect1><title>MCA Architecture</title>
+	<sect2><title>MCA Device Functions</title>
+           <para>
+              Refer to the file arch/i386/kernel/mca.c for more information.
+           </para>
+<!-- FIXME: Removed for now since no structured comments in source
+X!Earch/i386/kernel/mca.c
+-->
+	</sect2>
+	<sect2><title>MCA Bus DMA</title>
+!Iinclude/asm-i386/mca_dma.h
+	</sect2>
+     </sect1>
+  </chapter>
+
+  <chapter id="devfs">
+     <title>The Device File System</title>
+!Efs/devfs/base.c
+  </chapter>
+
+  <chapter id="security">
+     <title>Security Framework</title>
+!Esecurity/security.c
+  </chapter>
+
+  <chapter id="pmfuncs">
+     <title>Power Management</title>
+!Ekernel/power/pm.c
+  </chapter>
+
+  <chapter id="blkdev">
+     <title>Block Devices</title>
+!Edrivers/block/ll_rw_blk.c
+  </chapter>
+
+  <chapter id="miscdev">
+     <title>Miscellaneous Devices</title>
+!Edrivers/char/misc.c
+  </chapter>
+
+  <chapter id="viddev">
+     <title>Video4Linux</title>
+!Edrivers/media/video/videodev.c
+  </chapter>
+
+  <chapter id="snddev">
+     <title>Sound Devices</title>
+!Esound/sound_core.c
+<!-- FIXME: Removed for now since no structured comments in source
+X!Isound/sound_firmware.c
+-->
+  </chapter>
+
+  <chapter id="uart16x50">
+     <title>16x50 UART Driver</title>
+!Edrivers/serial/serial_core.c
+!Edrivers/serial/8250.c
+  </chapter>
+
+  <chapter id="z85230">
+     <title>Z85230 Support Library</title>
+!Edrivers/net/wan/z85230.c
+  </chapter>
+
+  <chapter id="fbdev">
+     <title>Frame Buffer Library</title>
+
+     <para>
+       The frame buffer drivers depend heavily on four data structures.  
+       These structures are declared in include/linux/fb.h.  They are 
+       fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs. 
+       The last three can be made available to and from userland. 
+     </para>
+
+     <para>
+       fb_info defines the current state of a particular video card. 
+       Inside fb_info, there exists a fb_ops structure which is a 
+       collection of needed functions to make fbdev and fbcon work.
+       fb_info is only visible to the kernel.
+     </para>
+
+     <para>
+       fb_var_screeninfo is used to describe the features of a video card 
+       that are user defined.  With fb_var_screeninfo, things such as
+       depth and the resolution may be defined.
+     </para>
+
+     <para>
+       The next structure is fb_fix_screeninfo. This defines the 
+       properties of a card that are created when a mode is set and can't 
+       be changed otherwise.  A good example of this is the start of the 
+       frame buffer memory.  This "locks" the address of the frame buffer
+       memory, so that it cannot be changed or moved.
+     </para>
+
+     <para>
+       The last structure is fb_monospecs. In the old API, there was 
+       little importance for fb_monospecs. This allowed for forbidden things 
+       such as setting a mode of 800x600 on a fix frequency monitor. With 
+       the new API, fb_monospecs prevents such things, and if used 
+       correctly, can prevent a monitor from being cooked.  fb_monospecs
+       will not be useful until kernels 2.5.x.
+     </para>
+
+     <sect1><title>Frame Buffer Memory</title>
+!Edrivers/video/fbmem.c
+     </sect1>
+     <sect1><title>Frame Buffer Console</title>
+!Edrivers/video/console/fbcon.c
+     </sect1>
+     <sect1><title>Frame Buffer Colormap</title>
+!Edrivers/video/fbcmap.c
+     </sect1>
+<!-- FIXME:
+  drivers/video/fbgen.c has no docs, which stuffs up the sgml.  Comment
+  out until somebody adds docs.  KAO
+     <sect1><title>Frame Buffer Generic Functions</title>
+X!Idrivers/video/fbgen.c
+     </sect1>
+KAO -->
+     <sect1><title>Frame Buffer Video Mode Database</title>
+!Idrivers/video/modedb.c
+!Edrivers/video/modedb.c
+     </sect1>
+     <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
+!Idrivers/video/macmodes.c
+     </sect1>
+     <sect1><title>Frame Buffer Fonts</title>
+        <para>
+           Refer to the file drivers/video/console/fonts.c for more information.
+        </para>
+<!-- FIXME: Removed for now since no structured comments in source
+X!Idrivers/video/console/fonts.c
+-->
+     </sect1>
+  </chapter>
+</book>
diff --git a/Documentation/DocBook/kernel-hacking.tmpl b/Documentation/DocBook/kernel-hacking.tmpl
new file mode 100644
index 000000000000..49a9ef82d575
--- /dev/null
+++ b/Documentation/DocBook/kernel-hacking.tmpl
@@ -0,0 +1,1349 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="lk-hacking-guide">
+ <bookinfo>
+  <title>Unreliable Guide To Hacking The Linux Kernel</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Paul</firstname>
+    <othername>Rusty</othername>
+    <surname>Russell</surname>
+    <affiliation>
+     <address>
+      <email>rusty@rustcorp.com.au</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2001</year>
+   <holder>Rusty Russell</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+    This documentation is free software; you can redistribute
+    it and/or modify it under the terms of the GNU General Public
+    License as published by the Free Software Foundation; either
+    version 2 of the License, or (at your option) any later
+    version.
+   </para>
+   
+   <para>
+    This program is distributed in the hope that it will be
+    useful, but WITHOUT ANY WARRANTY; without even the implied
+    warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+    See the GNU General Public License for more details.
+   </para>
+   
+   <para>
+    You should have received a copy of the GNU General Public
+    License along with this program; if not, write to the Free
+    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+    MA 02111-1307 USA
+   </para>
+   
+   <para>
+    For more details see the file COPYING in the source
+    distribution of Linux.
+   </para>
+  </legalnotice>
+
+  <releaseinfo>
+   This is the first release of this document as part of the kernel tarball.
+  </releaseinfo>
+
+ </bookinfo>
+
+ <toc></toc>
+
+ <chapter id="introduction">
+  <title>Introduction</title>
+  <para>
+   Welcome, gentle reader, to Rusty's Unreliable Guide to Linux
+   Kernel Hacking.  This document describes the common routines and
+   general requirements for kernel code: its goal is to serve as a
+   primer for Linux kernel development for experienced C
+   programmers.  I avoid implementation details: that's what the
+   code is for, and I ignore whole tracts of useful routines.
+  </para>
+  <para>
+   Before you read this, please understand that I never wanted to
+   write this document, being grossly under-qualified, but I always
+   wanted to read it, and this was the only way.  I hope it will
+   grow into a compendium of best practice, common starting points
+   and random information.
+  </para>
+ </chapter>
+
+ <chapter id="basic-players">
+  <title>The Players</title>
+
+  <para>
+   At any time each of the CPUs in a system can be:
+  </para>
+
+  <itemizedlist>
+   <listitem>
+    <para>
+     not associated with any process, serving a hardware interrupt;
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     not associated with any process, serving a softirq, tasklet or bh;
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     running in kernel space, associated with a process;
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     running a process in user space.
+    </para>
+   </listitem>
+  </itemizedlist>
+
+  <para>
+   There is a strict ordering between these: other than the last
+   category (userspace) each can only be pre-empted by those above.
+   For example, while a softirq is running on a CPU, no other
+   softirq will pre-empt it, but a hardware interrupt can.  However,
+   any other CPUs in the system execute independently.
+  </para>
+
+  <para>
+   We'll see a number of ways that the user context can block
+   interrupts, to become truly non-preemptable.
+  </para>
+  
+  <sect1 id="basics-usercontext">
+   <title>User Context</title>
+
+   <para>
+    User context is when you are coming in from a system call or
+    other trap: you can sleep, and you own the CPU (except for
+    interrupts) until you call <function>schedule()</function>.  
+    In other words, user context (unlike userspace) is not pre-emptable.
+   </para>
+
+   <note>
+    <para>
+     You are always in user context on module load and unload,
+     and on operations on the block device layer.
+    </para>
+   </note>
+
+   <para>
+    In user context, the <varname>current</varname> pointer (indicating 
+    the task we are currently executing) is valid, and
+    <function>in_interrupt()</function>
+    (<filename>include/linux/interrupt.h</filename>) is <returnvalue>false
+    </returnvalue>.  
+   </para>
+
+   <caution>
+    <para>
+     Beware that if you have interrupts or bottom halves disabled 
+     (see below), <function>in_interrupt()</function> will return a 
+     false positive.
+    </para>
+   </caution>
+  </sect1>
+
+  <sect1 id="basics-hardirqs">
+   <title>Hardware Interrupts (Hard IRQs)</title>
+
+   <para>
+    Timer ticks, <hardware>network cards</hardware> and 
+    <hardware>keyboard</hardware> are examples of real
+    hardware which produce interrupts at any time.  The kernel runs
+    interrupt handlers, which services the hardware.  The kernel
+    guarantees that this handler is never re-entered: if another
+    interrupt arrives, it is queued (or dropped).  Because it
+    disables interrupts, this handler has to be fast: frequently it
+    simply acknowledges the interrupt, marks a `software interrupt'
+    for execution and exits.
+   </para>
+
+   <para>
+    You can tell you are in a hardware interrupt, because 
+    <function>in_irq()</function> returns <returnvalue>true</returnvalue>.  
+   </para>
+   <caution>
+    <para>
+     Beware that this will return a false positive if interrupts are disabled 
+     (see below).
+    </para>
+   </caution>
+  </sect1>
+
+  <sect1 id="basics-softirqs">
+   <title>Software Interrupt Context: Bottom Halves, Tasklets, softirqs</title>
+
+   <para>
+    Whenever a system call is about to return to userspace, or a
+    hardware interrupt handler exits, any `software interrupts'
+    which are marked pending (usually by hardware interrupts) are
+    run (<filename>kernel/softirq.c</filename>).
+   </para>
+
+   <para>
+    Much of the real interrupt handling work is done here.  Early in
+    the transition to <acronym>SMP</acronym>, there were only `bottom 
+    halves' (BHs), which didn't take advantage of multiple CPUs.  Shortly 
+    after we switched from wind-up computers made of match-sticks and snot,
+    we abandoned this limitation.
+   </para>
+
+   <para>
+    <filename class="headerfile">include/linux/interrupt.h</filename> lists the
+    different BH's.  No matter how many CPUs you have, no two BHs will run at 
+    the same time. This made the transition to SMP simpler, but sucks hard for
+    scalable performance.  A very important bottom half is the timer
+    BH (<filename class="headerfile">include/linux/timer.h</filename>): you
+    can register to have it call functions for you in a given length of time.
+   </para>
+
+   <para>
+    2.3.43 introduced softirqs, and re-implemented the (now
+    deprecated) BHs underneath them.  Softirqs are fully-SMP
+    versions of BHs: they can run on as many CPUs at once as
+    required.  This means they need to deal with any races in shared
+    data using their own locks.  A bitmask is used to keep track of
+    which are enabled, so the 32 available softirqs should not be
+    used up lightly.  (<emphasis>Yes</emphasis>, people will
+    notice).
+   </para>
+
+   <para>
+    tasklets (<filename class="headerfile">include/linux/interrupt.h</filename>)
+    are like softirqs, except they are dynamically-registrable (meaning you 
+    can have as many as you want), and they also guarantee that any tasklet 
+    will only run on one CPU at any time, although different tasklets can 
+    run simultaneously (unlike different BHs).  
+   </para>
+   <caution>
+    <para>
+     The name `tasklet' is misleading: they have nothing to do with `tasks', 
+     and probably more to do with some bad vodka Alexey Kuznetsov had at the 
+     time.
+    </para>
+   </caution>
+
+   <para>
+    You can tell you are in a softirq (or bottom half, or tasklet)
+    using the <function>in_softirq()</function> macro 
+    (<filename class="headerfile">include/linux/interrupt.h</filename>).
+   </para>
+   <caution>
+    <para>
+     Beware that this will return a false positive if a bh lock (see below)
+     is held.
+    </para>
+   </caution>
+  </sect1>
+ </chapter>
+
+ <chapter id="basic-rules">
+  <title>Some Basic Rules</title>
+
+  <variablelist>
+   <varlistentry>
+    <term>No memory protection</term>
+    <listitem>
+     <para>
+      If you corrupt memory, whether in user context or
+      interrupt context, the whole machine will crash.  Are you
+      sure you can't do what you want in userspace?
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term>No floating point or <acronym>MMX</acronym></term>
+    <listitem>
+     <para>
+      The <acronym>FPU</acronym> context is not saved; even in user
+      context the <acronym>FPU</acronym> state probably won't
+      correspond with the current process: you would mess with some
+      user process' <acronym>FPU</acronym> state.  If you really want
+      to do this, you would have to explicitly save/restore the full
+      <acronym>FPU</acronym> state (and avoid context switches).  It
+      is generally a bad idea; use fixed point arithmetic first.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term>A rigid stack limit</term>
+    <listitem>
+     <para>
+      The kernel stack is about 6K in 2.2 (for most
+      architectures: it's about 14K on the Alpha), and shared
+      with interrupts so you can't use it all.  Avoid deep
+      recursion and huge local arrays on the stack (allocate
+      them dynamically instead).
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term>The Linux kernel is portable</term>
+    <listitem>
+     <para>
+      Let's keep it that way.  Your code should be 64-bit clean,
+      and endian-independent.  You should also minimize CPU
+      specific stuff, e.g. inline assembly should be cleanly
+      encapsulated and minimized to ease porting.  Generally it
+      should be restricted to the architecture-dependent part of
+      the kernel tree.
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </chapter>
+
+ <chapter id="ioctls">
+  <title>ioctls: Not writing a new system call</title>
+
+  <para>
+   A system call generally looks like this
+  </para>
+
+  <programlisting>
+asmlinkage long sys_mycall(int arg)
+{
+        return 0; 
+}
+  </programlisting>
+
+  <para>
+   First, in most cases you don't want to create a new system call.
+   You create a character device and implement an appropriate ioctl
+   for it.  This is much more flexible than system calls, doesn't have
+   to be entered in every architecture's
+   <filename class="headerfile">include/asm/unistd.h</filename> and
+   <filename>arch/kernel/entry.S</filename> file, and is much more
+   likely to be accepted by Linus.
+  </para>
+
+  <para>
+   If all your routine does is read or write some parameter, consider
+   implementing a <function>sysctl</function> interface instead.
+  </para>
+
+  <para>
+   Inside the ioctl you're in user context to a process.  When a
+   error occurs you return a negated errno (see
+   <filename class="headerfile">include/linux/errno.h</filename>),
+   otherwise you return <returnvalue>0</returnvalue>.
+  </para>
+
+  <para>
+   After you slept you should check if a signal occurred: the
+   Unix/Linux way of handling signals is to temporarily exit the
+   system call with the <constant>-ERESTARTSYS</constant> error.  The
+   system call entry code will switch back to user context, process
+   the signal handler and then your system call will be restarted
+   (unless the user disabled that).  So you should be prepared to
+   process the restart, e.g. if you're in the middle of manipulating
+   some data structure.
+  </para>
+
+  <programlisting>
+if (signal_pending()) 
+        return -ERESTARTSYS;
+  </programlisting>
+
+  <para>
+   If you're doing longer computations: first think userspace. If you
+   <emphasis>really</emphasis> want to do it in kernel you should
+   regularly check if you need to give up the CPU (remember there is
+   cooperative multitasking per CPU).  Idiom:
+  </para>
+
+  <programlisting>
+cond_resched(); /* Will sleep */ 
+  </programlisting>
+
+  <para>
+   A short note on interface design: the UNIX system call motto is
+   "Provide mechanism not policy".
+  </para>
+ </chapter>
+
+ <chapter id="deadlock-recipes">
+  <title>Recipes for Deadlock</title>
+
+  <para>
+   You cannot call any routines which may sleep, unless:
+  </para>
+  <itemizedlist>
+   <listitem>
+    <para>
+     You are in user context.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     You do not own any spinlocks.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     You have interrupts enabled (actually, Andi Kleen says
+     that the scheduling code will enable them for you, but
+     that's probably not what you wanted).
+    </para>
+   </listitem>
+  </itemizedlist>
+
+  <para>
+   Note that some functions may sleep implicitly: common ones are
+   the user space access functions (*_user) and memory allocation
+   functions without <symbol>GFP_ATOMIC</symbol>.
+  </para>
+
+  <para>
+   You will eventually lock up your box if you break these rules.  
+  </para>
+
+  <para>
+   Really.
+  </para>
+ </chapter>
+
+ <chapter id="common-routines">
+  <title>Common Routines</title>
+
+  <sect1 id="routines-printk">
+   <title>
+    <function>printk()</function>
+    <filename class="headerfile">include/linux/kernel.h</filename>
+   </title>
+
+   <para>
+    <function>printk()</function> feeds kernel messages to the
+    console, dmesg, and the syslog daemon.  It is useful for debugging
+    and reporting errors, and can be used inside interrupt context,
+    but use with caution: a machine which has its console flooded with
+    printk messages is unusable.  It uses a format string mostly
+    compatible with ANSI C printf, and C string concatenation to give
+    it a first "priority" argument:
+   </para>
+
+   <programlisting>
+printk(KERN_INFO "i = %u\n", i);
+   </programlisting>
+
+   <para>
+    See <filename class="headerfile">include/linux/kernel.h</filename>;
+    for other KERN_ values; these are interpreted by syslog as the
+    level.  Special case: for printing an IP address use
+   </para>
+
+   <programlisting>
+__u32 ipaddress;
+printk(KERN_INFO "my ip: %d.%d.%d.%d\n", NIPQUAD(ipaddress));
+   </programlisting>
+
+   <para>
+    <function>printk()</function> internally uses a 1K buffer and does
+    not catch overruns.  Make sure that will be enough.
+   </para>
+
+   <note>
+    <para>
+     You will know when you are a real kernel hacker
+     when you start typoing printf as printk in your user programs :)
+    </para>
+   </note>
+
+   <!--- From the Lions book reader department --> 
+
+   <note>
+    <para>
+     Another sidenote: the original Unix Version 6 sources had a
+     comment on top of its printf function: "Printf should not be
+     used for chit-chat".  You should follow that advice.
+    </para>
+   </note>
+  </sect1>
+
+  <sect1 id="routines-copy">
+   <title>
+    <function>copy_[to/from]_user()</function>
+    /
+    <function>get_user()</function>
+    /
+    <function>put_user()</function>
+    <filename class="headerfile">include/asm/uaccess.h</filename>
+   </title>  
+
+   <para>
+    <emphasis>[SLEEPS]</emphasis>
+   </para>
+
+   <para>
+    <function>put_user()</function> and <function>get_user()</function>
+    are used to get and put single values (such as an int, char, or
+    long) from and to userspace.  A pointer into userspace should
+    never be simply dereferenced: data should be copied using these
+    routines.  Both return <constant>-EFAULT</constant> or 0.
+   </para>
+   <para>
+    <function>copy_to_user()</function> and
+    <function>copy_from_user()</function> are more general: they copy
+    an arbitrary amount of data to and from userspace.
+    <caution>
+     <para>
+      Unlike <function>put_user()</function> and
+      <function>get_user()</function>, they return the amount of
+      uncopied data (ie. <returnvalue>0</returnvalue> still means
+      success).
+     </para>
+    </caution>
+    [Yes, this moronic interface makes me cringe.  Please submit a
+    patch and become my hero --RR.]
+   </para>
+   <para>
+    The functions may sleep implicitly. This should never be called
+    outside user context (it makes no sense), with interrupts
+    disabled, or a spinlock held.
+   </para>
+  </sect1>
+
+  <sect1 id="routines-kmalloc">
+   <title><function>kmalloc()</function>/<function>kfree()</function>
+    <filename class="headerfile">include/linux/slab.h</filename></title>
+
+   <para>
+    <emphasis>[MAY SLEEP: SEE BELOW]</emphasis>
+   </para>
+
+   <para>
+    These routines are used to dynamically request pointer-aligned
+    chunks of memory, like malloc and free do in userspace, but
+    <function>kmalloc()</function> takes an extra flag word.
+    Important values:
+   </para>
+
+   <variablelist>
+    <varlistentry>
+     <term>
+      <constant>
+       GFP_KERNEL
+      </constant>
+     </term>
+     <listitem>
+      <para>
+       May sleep and swap to free memory. Only allowed in user
+       context, but is the most reliable way to allocate memory.
+      </para>
+     </listitem>
+    </varlistentry>
+    
+    <varlistentry>
+     <term>
+      <constant>
+       GFP_ATOMIC
+      </constant>
+     </term>
+     <listitem>
+      <para>
+       Don't sleep. Less reliable than <constant>GFP_KERNEL</constant>,
+       but may be called from interrupt context. You should
+       <emphasis>really</emphasis> have a good out-of-memory
+       error-handling strategy.
+      </para>
+     </listitem>
+    </varlistentry>
+    
+    <varlistentry>
+     <term>
+      <constant>
+       GFP_DMA
+      </constant>
+     </term>
+     <listitem>
+      <para>
+       Allocate ISA DMA lower than 16MB. If you don't know what that
+       is you don't need it.  Very unreliable.
+      </para>
+     </listitem>
+    </varlistentry>
+   </variablelist>
+
+   <para>
+    If you see a <errorname>kmem_grow: Called nonatomically from int
+    </errorname> warning message you called a memory allocation function
+    from interrupt context without <constant>GFP_ATOMIC</constant>.
+    You should really fix that.  Run, don't walk.
+   </para>
+
+   <para>
+    If you are allocating at least <constant>PAGE_SIZE</constant>
+    (<filename class="headerfile">include/asm/page.h</filename>) bytes,
+    consider using <function>__get_free_pages()</function>
+
+    (<filename class="headerfile">include/linux/mm.h</filename>).  It
+    takes an order argument (0 for page sized, 1 for double page, 2
+    for four pages etc.) and the same memory priority flag word as
+    above.
+   </para>
+
+   <para>
+    If you are allocating more than a page worth of bytes you can use
+    <function>vmalloc()</function>.  It'll allocate virtual memory in
+    the kernel map.  This block is not contiguous in physical memory,
+    but the <acronym>MMU</acronym> makes it look like it is for you
+    (so it'll only look contiguous to the CPUs, not to external device
+    drivers).  If you really need large physically contiguous memory
+    for some weird device, you have a problem: it is poorly supported
+    in Linux because after some time memory fragmentation in a running
+    kernel makes it hard.  The best way is to allocate the block early
+    in the boot process via the <function>alloc_bootmem()</function>
+    routine.
+   </para>
+
+   <para>
+    Before inventing your own cache of often-used objects consider
+    using a slab cache in
+    <filename class="headerfile">include/linux/slab.h</filename>
+   </para>
+  </sect1>
+
+  <sect1 id="routines-current">
+   <title><function>current</function>
+    <filename class="headerfile">include/asm/current.h</filename></title>
+
+   <para>
+    This global variable (really a macro) contains a pointer to
+    the current task structure, so is only valid in user context.
+    For example, when a process makes a system call, this will
+    point to the task structure of the calling process.  It is
+    <emphasis>not NULL</emphasis> in interrupt context.
+   </para>
+  </sect1>
+
+  <sect1 id="routines-udelay">
+   <title><function>udelay()</function>/<function>mdelay()</function>
+     <filename class="headerfile">include/asm/delay.h</filename>
+     <filename class="headerfile">include/linux/delay.h</filename>
+   </title>
+
+   <para>
+    The <function>udelay()</function> function can be used for small pauses.
+    Do not use large values with <function>udelay()</function> as you risk
+    overflow - the helper function <function>mdelay()</function> is useful
+    here, or even consider <function>schedule_timeout()</function>.
+   </para> 
+  </sect1>
+ 
+  <sect1 id="routines-endian">
+   <title><function>cpu_to_be32()</function>/<function>be32_to_cpu()</function>/<function>cpu_to_le32()</function>/<function>le32_to_cpu()</function>
+     <filename class="headerfile">include/asm/byteorder.h</filename>
+   </title>
+
+   <para>
+    The <function>cpu_to_be32()</function> family (where the "32" can
+    be replaced by 64 or 16, and the "be" can be replaced by "le") are
+    the general way to do endian conversions in the kernel: they
+    return the converted value.  All variations supply the reverse as
+    well: <function>be32_to_cpu()</function>, etc.
+   </para>
+
+   <para>
+    There are two major variations of these functions: the pointer
+    variation, such as <function>cpu_to_be32p()</function>, which take
+    a pointer to the given type, and return the converted value.  The
+    other variation is the "in-situ" family, such as
+    <function>cpu_to_be32s()</function>, which convert value referred
+    to by the pointer, and return void.
+   </para> 
+  </sect1>
+
+  <sect1 id="routines-local-irqs">
+   <title><function>local_irq_save()</function>/<function>local_irq_restore()</function>
+    <filename class="headerfile">include/asm/system.h</filename>
+   </title>
+
+   <para>
+    These routines disable hard interrupts on the local CPU, and
+    restore them.  They are reentrant; saving the previous state in
+    their one <varname>unsigned long flags</varname> argument.  If you
+    know that interrupts are enabled, you can simply use
+    <function>local_irq_disable()</function> and
+    <function>local_irq_enable()</function>.
+   </para>
+  </sect1>
+
+  <sect1 id="routines-softirqs">
+   <title><function>local_bh_disable()</function>/<function>local_bh_enable()</function>
+    <filename class="headerfile">include/linux/interrupt.h</filename></title>
+
+   <para>
+    These routines disable soft interrupts on the local CPU, and
+    restore them.  They are reentrant; if soft interrupts were
+    disabled before, they will still be disabled after this pair
+    of functions has been called.  They prevent softirqs, tasklets
+    and bottom halves from running on the current CPU.
+   </para>
+  </sect1>
+
+  <sect1 id="routines-processorids">
+   <title><function>smp_processor_id</function>()
+    <filename class="headerfile">include/asm/smp.h</filename></title>
+   
+   <para>
+    <function>smp_processor_id()</function> returns the current
+    processor number, between 0 and <symbol>NR_CPUS</symbol> (the
+    maximum number of CPUs supported by Linux, currently 32).  These
+    values are not necessarily continuous.
+   </para>
+  </sect1>
+
+  <sect1 id="routines-init">
+   <title><type>__init</type>/<type>__exit</type>/<type>__initdata</type>
+    <filename class="headerfile">include/linux/init.h</filename></title>
+
+   <para>
+    After boot, the kernel frees up a special section; functions
+    marked with <type>__init</type> and data structures marked with
+    <type>__initdata</type> are dropped after boot is complete (within
+    modules this directive is currently ignored).  <type>__exit</type>
+    is used to declare a function which is only required on exit: the
+    function will be dropped if this file is not compiled as a module.
+    See the header file for use. Note that it makes no sense for a function
+    marked with <type>__init</type> to be exported to modules with 
+    <function>EXPORT_SYMBOL()</function> - this will break.
+   </para>
+   <para>
+   Static data structures marked as <type>__initdata</type> must be initialised
+   (as opposed to ordinary static data which is zeroed BSS) and cannot be 
+   <type>const</type>.
+   </para> 
+
+  </sect1>
+
+  <sect1 id="routines-init-again">
+   <title><function>__initcall()</function>/<function>module_init()</function>
+    <filename class="headerfile">include/linux/init.h</filename></title>
+   <para>
+    Many parts of the kernel are well served as a module
+    (dynamically-loadable parts of the kernel).  Using the
+    <function>module_init()</function> and
+    <function>module_exit()</function> macros it is easy to write code
+    without #ifdefs which can operate both as a module or built into
+    the kernel.
+   </para>
+
+   <para>
+    The <function>module_init()</function> macro defines which
+    function is to be called at module insertion time (if the file is
+    compiled as a module), or at boot time: if the file is not
+    compiled as a module the <function>module_init()</function> macro
+    becomes equivalent to <function>__initcall()</function>, which
+    through linker magic ensures that the function is called on boot.
+   </para>
+
+   <para>
+    The function can return a negative error number to cause
+    module loading to fail (unfortunately, this has no effect if
+    the module is compiled into the kernel).  For modules, this is
+    called in user context, with interrupts enabled, and the
+    kernel lock held, so it can sleep.
+   </para>
+  </sect1>
+  
+  <sect1 id="routines-moduleexit">
+   <title> <function>module_exit()</function>
+    <filename class="headerfile">include/linux/init.h</filename> </title>
+
+   <para>
+    This macro defines the function to be called at module removal
+    time (or never, in the case of the file compiled into the
+    kernel).  It will only be called if the module usage count has
+    reached zero.  This function can also sleep, but cannot fail:
+    everything must be cleaned up by the time it returns.
+   </para>
+  </sect1>
+
+ <!-- add info on new-style module refcounting here -->
+ </chapter>
+
+ <chapter id="queues">
+  <title>Wait Queues
+   <filename class="headerfile">include/linux/wait.h</filename>
+  </title>
+  <para>
+   <emphasis>[SLEEPS]</emphasis>
+  </para>
+
+  <para>
+   A wait queue is used to wait for someone to wake you up when a
+   certain condition is true.  They must be used carefully to ensure
+   there is no race condition.  You declare a
+   <type>wait_queue_head_t</type>, and then processes which want to
+   wait for that condition declare a <type>wait_queue_t</type>
+   referring to themselves, and place that in the queue.
+  </para>
+
+  <sect1 id="queue-declaring">
+   <title>Declaring</title>
+   
+   <para>
+    You declare a <type>wait_queue_head_t</type> using the
+    <function>DECLARE_WAIT_QUEUE_HEAD()</function> macro, or using the
+    <function>init_waitqueue_head()</function> routine in your
+    initialization code.
+   </para>
+  </sect1>
+  
+  <sect1 id="queue-waitqueue">
+   <title>Queuing</title>
+   
+   <para>
+    Placing yourself in the waitqueue is fairly complex, because you
+    must put yourself in the queue before checking the condition.
+    There is a macro to do this:
+    <function>wait_event_interruptible()</function>
+
+    <filename class="headerfile">include/linux/sched.h</filename> The
+    first argument is the wait queue head, and the second is an
+    expression which is evaluated; the macro returns
+    <returnvalue>0</returnvalue> when this expression is true, or
+    <returnvalue>-ERESTARTSYS</returnvalue> if a signal is received.
+    The <function>wait_event()</function> version ignores signals.
+   </para>
+   <para>
+   Do not use the <function>sleep_on()</function> function family -
+   it is very easy to accidentally introduce races; almost certainly
+   one of the <function>wait_event()</function> family will do, or a
+   loop around <function>schedule_timeout()</function>. If you choose
+   to loop around <function>schedule_timeout()</function> remember
+   you must set the task state (with 
+   <function>set_current_state()</function>) on each iteration to avoid
+   busy-looping.
+   </para>
+ 
+  </sect1>
+
+  <sect1 id="queue-waking">
+   <title>Waking Up Queued Tasks</title>
+   
+   <para>
+    Call <function>wake_up()</function>
+
+    <filename class="headerfile">include/linux/sched.h</filename>;,
+    which will wake up every process in the queue.  The exception is
+    if one has <constant>TASK_EXCLUSIVE</constant> set, in which case
+    the remainder of the queue will not be woken.
+   </para>
+  </sect1>
+ </chapter>
+
+ <chapter id="atomic-ops">
+  <title>Atomic Operations</title>
+
+  <para>
+   Certain operations are guaranteed atomic on all platforms.  The
+   first class of operations work on <type>atomic_t</type>
+
+   <filename class="headerfile">include/asm/atomic.h</filename>; this
+   contains a signed integer (at least 24 bits long), and you must use
+   these functions to manipulate or read atomic_t variables.
+   <function>atomic_read()</function> and
+   <function>atomic_set()</function> get and set the counter,
+   <function>atomic_add()</function>,
+   <function>atomic_sub()</function>,
+   <function>atomic_inc()</function>,
+   <function>atomic_dec()</function>, and
+   <function>atomic_dec_and_test()</function> (returns
+   <returnvalue>true</returnvalue> if it was decremented to zero).
+  </para>
+
+  <para>
+   Yes.  It returns <returnvalue>true</returnvalue> (i.e. != 0) if the
+   atomic variable is zero.
+  </para>
+
+  <para>
+   Note that these functions are slower than normal arithmetic, and
+   so should not be used unnecessarily.  On some platforms they
+   are much slower, like 32-bit Sparc where they use a spinlock.
+  </para>
+
+  <para>
+   The second class of atomic operations is atomic bit operations on a
+   <type>long</type>, defined in
+
+   <filename class="headerfile">include/linux/bitops.h</filename>.  These
+   operations generally take a pointer to the bit pattern, and a bit
+   number: 0 is the least significant bit.
+   <function>set_bit()</function>, <function>clear_bit()</function>
+   and <function>change_bit()</function> set, clear, and flip the
+   given bit.  <function>test_and_set_bit()</function>,
+   <function>test_and_clear_bit()</function> and
+   <function>test_and_change_bit()</function> do the same thing,
+   except return true if the bit was previously set; these are
+   particularly useful for very simple locking.
+  </para>
+  
+  <para>
+   It is possible to call these operations with bit indices greater
+   than BITS_PER_LONG.  The resulting behavior is strange on big-endian
+   platforms though so it is a good idea not to do this.
+  </para>
+
+  <para>
+   Note that the order of bits depends on the architecture, and in
+   particular, the bitfield passed to these operations must be at
+   least as large as a <type>long</type>.
+  </para>
+ </chapter>
+
+ <chapter id="symbols">
+  <title>Symbols</title>
+
+  <para>
+   Within the kernel proper, the normal linking rules apply
+   (ie. unless a symbol is declared to be file scope with the
+   <type>static</type> keyword, it can be used anywhere in the
+   kernel).  However, for modules, a special exported symbol table is
+   kept which limits the entry points to the kernel proper.  Modules
+   can also export symbols.
+  </para>
+
+  <sect1 id="sym-exportsymbols">
+   <title><function>EXPORT_SYMBOL()</function>
+    <filename class="headerfile">include/linux/module.h</filename></title>
+
+   <para>
+    This is the classic method of exporting a symbol, and it works
+    for both modules and non-modules.  In the kernel all these
+    declarations are often bundled into a single file to help
+    genksyms (which searches source files for these declarations).
+    See the comment on genksyms and Makefiles below.
+   </para>
+  </sect1>
+
+  <sect1 id="sym-exportsymbols-gpl">
+   <title><function>EXPORT_SYMBOL_GPL()</function>
+    <filename class="headerfile">include/linux/module.h</filename></title>
+
+   <para>
+    Similar to <function>EXPORT_SYMBOL()</function> except that the
+    symbols exported by <function>EXPORT_SYMBOL_GPL()</function> can
+    only be seen by modules with a
+    <function>MODULE_LICENSE()</function> that specifies a GPL
+    compatible license.
+   </para>
+  </sect1>
+ </chapter>
+
+ <chapter id="conventions">
+  <title>Routines and Conventions</title>
+
+  <sect1 id="conventions-doublelinkedlist">
+   <title>Double-linked lists
+    <filename class="headerfile">include/linux/list.h</filename></title>
+
+   <para>
+    There are three sets of linked-list routines in the kernel
+    headers, but this one seems to be winning out (and Linus has
+    used it).  If you don't have some particular pressing need for
+    a single list, it's a good choice.  In fact, I don't care
+    whether it's a good choice or not, just use it so we can get
+    rid of the others.
+   </para>
+  </sect1>
+
+  <sect1 id="convention-returns">
+   <title>Return Conventions</title>
+
+   <para>
+    For code called in user context, it's very common to defy C
+    convention, and return <returnvalue>0</returnvalue> for success,
+    and a negative error number
+    (eg. <returnvalue>-EFAULT</returnvalue>) for failure.  This can be
+    unintuitive at first, but it's fairly widespread in the networking
+    code, for example.
+   </para>
+
+   <para>
+    The filesystem code uses <function>ERR_PTR()</function>
+
+    <filename class="headerfile">include/linux/fs.h</filename>; to
+    encode a negative error number into a pointer, and
+    <function>IS_ERR()</function> and <function>PTR_ERR()</function>
+    to get it back out again: avoids a separate pointer parameter for
+    the error number.  Icky, but in a good way.
+   </para>
+  </sect1>
+
+  <sect1 id="conventions-borkedcompile">
+   <title>Breaking Compilation</title>
+
+   <para>
+    Linus and the other developers sometimes change function or
+    structure names in development kernels; this is not done just to
+    keep everyone on their toes: it reflects a fundamental change
+    (eg. can no longer be called with interrupts on, or does extra
+    checks, or doesn't do checks which were caught before).  Usually
+    this is accompanied by a fairly complete note to the linux-kernel
+    mailing list; search the archive.  Simply doing a global replace
+    on the file usually makes things <emphasis>worse</emphasis>.
+   </para>
+  </sect1>
+
+  <sect1 id="conventions-initialising">
+   <title>Initializing structure members</title>
+
+   <para>
+    The preferred method of initializing structures is to use
+    designated initialisers, as defined by ISO C99, eg:
+   </para>
+   <programlisting>
+static struct block_device_operations opt_fops = {
+        .open               = opt_open,
+        .release            = opt_release,
+        .ioctl              = opt_ioctl,
+        .check_media_change = opt_media_change,
+};
+   </programlisting>
+   <para>
+    This makes it easy to grep for, and makes it clear which
+    structure fields are set.  You should do this because it looks
+    cool.
+   </para>
+  </sect1>
+
+  <sect1 id="conventions-gnu-extns">
+   <title>GNU Extensions</title>
+
+   <para>
+    GNU Extensions are explicitly allowed in the Linux kernel.
+    Note that some of the more complex ones are not very well
+    supported, due to lack of general use, but the following are
+    considered standard (see the GCC info page section "C
+    Extensions" for more details - Yes, really the info page, the
+    man page is only a short summary of the stuff in info):
+   </para>
+   <itemizedlist>
+    <listitem>
+     <para>
+      Inline functions
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Statement expressions (ie. the ({ and }) constructs).
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Declaring attributes of a function / variable / type
+      (__attribute__)
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      typeof
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Zero length arrays
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Macro varargs
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Arithmetic on void pointers
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Non-Constant initializers
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Assembler Instructions (not outside arch/ and include/asm/)
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      Function names as strings (__FUNCTION__)
+     </para>
+    </listitem>
+    <listitem>
+     <para>
+      __builtin_constant_p()
+     </para>
+    </listitem>
+   </itemizedlist>
+
+   <para>
+    Be wary when using long long in the kernel, the code gcc generates for
+    it is horrible and worse: division and multiplication does not work
+    on i386 because the GCC runtime functions for it are missing from
+    the kernel environment.
+   </para>
+
+    <!-- FIXME: add a note about ANSI aliasing cleanness -->
+  </sect1>
+
+  <sect1 id="conventions-cplusplus">
+   <title>C++</title>
+   
+   <para>
+    Using C++ in the kernel is usually a bad idea, because the
+    kernel does not provide the necessary runtime environment
+    and the include files are not tested for it.  It is still
+    possible, but not recommended.  If you really want to do
+    this, forget about exceptions at least.
+   </para>
+  </sect1>
+
+  <sect1 id="conventions-ifdef">
+   <title>&num;if</title>
+   
+   <para>
+    It is generally considered cleaner to use macros in header files
+    (or at the top of .c files) to abstract away functions rather than
+    using `#if' pre-processor statements throughout the source code.
+   </para>
+  </sect1>
+ </chapter>
+
+ <chapter id="submitting">
+  <title>Putting Your Stuff in the Kernel</title>
+
+  <para>
+   In order to get your stuff into shape for official inclusion, or
+   even to make a neat patch, there's administrative work to be
+   done:
+  </para>
+  <itemizedlist>
+   <listitem>
+    <para>
+     Figure out whose pond you've been pissing in.  Look at the top of
+     the source files, inside the <filename>MAINTAINERS</filename>
+     file, and last of all in the <filename>CREDITS</filename> file.
+     You should coordinate with this person to make sure you're not
+     duplicating effort, or trying something that's already been
+     rejected.
+    </para>
+
+    <para>
+     Make sure you put your name and EMail address at the top of
+     any files you create or mangle significantly.  This is the
+     first place people will look when they find a bug, or when
+     <emphasis>they</emphasis> want to make a change.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Usually you want a configuration option for your kernel hack.
+     Edit <filename>Config.in</filename> in the appropriate directory
+     (but under <filename>arch/</filename> it's called
+     <filename>config.in</filename>).  The Config Language used is not
+     bash, even though it looks like bash; the safe way is to use only
+     the constructs that you already see in
+     <filename>Config.in</filename> files (see
+     <filename>Documentation/kbuild/kconfig-language.txt</filename>).
+     It's good to run "make xconfig" at least once to test (because
+     it's the only one with a static parser).
+    </para>
+
+    <para>
+     Variables which can be Y or N use <type>bool</type> followed by a
+     tagline and the config define name (which must start with
+     CONFIG_).  The <type>tristate</type> function is the same, but
+     allows the answer M (which defines
+     <symbol>CONFIG_foo_MODULE</symbol> in your source, instead of
+     <symbol>CONFIG_FOO</symbol>) if <symbol>CONFIG_MODULES</symbol>
+     is enabled.
+    </para>
+
+    <para>
+     You may well want to make your CONFIG option only visible if
+     <symbol>CONFIG_EXPERIMENTAL</symbol> is enabled: this serves as a
+     warning to users.  There many other fancy things you can do: see
+     the various <filename>Config.in</filename> files for ideas.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Edit the <filename>Makefile</filename>: the CONFIG variables are
+     exported here so you can conditionalize compilation with `ifeq'.
+     If your file exports symbols then add the names to
+     <varname>export-objs</varname> so that genksyms will find them.
+     <caution>
+      <para>
+       There is a restriction on the kernel build system that objects
+       which export symbols must have globally unique names.
+       If your object does not have a globally unique name then the
+       standard fix is to move the
+       <function>EXPORT_SYMBOL()</function> statements to their own
+       object with a unique name.
+       This is why several systems have separate exporting objects,
+       usually suffixed with ksyms.
+      </para>
+     </caution>
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Document your option in Documentation/Configure.help.  Mention
+     incompatibilities and issues here.  <emphasis> Definitely
+     </emphasis> end your description with <quote> if in doubt, say N
+     </quote> (or, occasionally, `Y'); this is for people who have no
+     idea what you are talking about.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Put yourself in <filename>CREDITS</filename> if you've done
+     something noteworthy, usually beyond a single file (your name
+     should be at the top of the source files anyway).
+     <filename>MAINTAINERS</filename> means you want to be consulted
+     when changes are made to a subsystem, and hear about bugs; it
+     implies a more-than-passing commitment to some part of the code.
+    </para>
+   </listitem>
+   
+   <listitem>
+    <para>
+     Finally, don't forget to read <filename>Documentation/SubmittingPatches</filename>
+     and possibly <filename>Documentation/SubmittingDrivers</filename>.
+    </para>
+   </listitem>
+  </itemizedlist>
+ </chapter>
+
+ <chapter id="cantrips">
+  <title>Kernel Cantrips</title>
+
+  <para>
+   Some favorites from browsing the source.  Feel free to add to this
+   list.
+  </para>
+
+  <para>
+   <filename>include/linux/brlock.h:</filename>
+  </para>
+  <programlisting>
+extern inline void br_read_lock (enum brlock_indices idx)
+{
+        /*
+         * This causes a link-time bug message if an
+         * invalid index is used:
+         */
+        if (idx >= __BR_END)
+                __br_lock_usage_bug();
+
+        read_lock(&amp;__brlock_array[smp_processor_id()][idx]);
+}
+  </programlisting>
+
+  <para>
+   <filename>include/linux/fs.h</filename>:
+  </para>
+  <programlisting>
+/*
+ * Kernel pointers have redundant information, so we can use a
+ * scheme where we can return either an error code or a dentry
+ * pointer with the same return value.
+ *
+ * This should be a per-architecture thing, to allow different
+ * error and pointer decisions.
+ */
+ #define ERR_PTR(err)    ((void *)((long)(err)))
+ #define PTR_ERR(ptr)    ((long)(ptr))
+ #define IS_ERR(ptr)     ((unsigned long)(ptr) > (unsigned long)(-1000))
+</programlisting>
+
+  <para>
+   <filename>include/asm-i386/uaccess.h:</filename>
+  </para>
+
+  <programlisting>
+#define copy_to_user(to,from,n)                         \
+        (__builtin_constant_p(n) ?                      \
+         __constant_copy_to_user((to),(from),(n)) :     \
+         __generic_copy_to_user((to),(from),(n)))
+  </programlisting>
+
+  <para>
+   <filename>arch/sparc/kernel/head.S:</filename>
+  </para>
+
+  <programlisting>
+/*
+ * Sun people can't spell worth damn. "compatability" indeed.
+ * At least we *know* we can't spell, and use a spell-checker.
+ */
+
+/* Uh, actually Linus it is I who cannot spell. Too much murky
+ * Sparc assembly will do this to ya.
+ */
+C_LABEL(cputypvar):
+        .asciz "compatability"
+
+/* Tested on SS-5, SS-10. Probably someone at Sun applied a spell-checker. */
+        .align 4
+C_LABEL(cputypvar_sun4m):
+        .asciz "compatible"
+  </programlisting>
+
+  <para>
+   <filename>arch/sparc/lib/checksum.S:</filename>
+  </para>
+
+  <programlisting>
+        /* Sun, you just can't beat me, you just can't.  Stop trying,
+         * give up.  I'm serious, I am going to kick the living shit
+         * out of you, game over, lights out.
+         */
+  </programlisting>
+ </chapter>
+
+ <chapter id="credits">
+  <title>Thanks</title>
+
+  <para>
+   Thanks to Andi Kleen for the idea, answering my questions, fixing
+   my mistakes, filling content, etc.  Philipp Rumpf for more spelling
+   and clarity fixes, and some excellent non-obvious points.  Werner
+   Almesberger for giving me a great summary of
+   <function>disable_irq()</function>, and Jes Sorensen and Andrea
+   Arcangeli added caveats. Michael Elizabeth Chastain for checking
+   and adding to the Configure section. <!-- Rusty insisted on this
+   bit; I didn't do it! --> Telsa Gwynne for teaching me DocBook. 
+  </para>
+ </chapter>
+</book>
+
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
new file mode 100644
index 000000000000..90dc2de8e0af
--- /dev/null
+++ b/Documentation/DocBook/kernel-locking.tmpl
@@ -0,0 +1,2088 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="LKLockingGuide">
+ <bookinfo>
+  <title>Unreliable Guide To Locking</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Rusty</firstname>
+    <surname>Russell</surname>
+    <affiliation>
+     <address>
+      <email>rusty@rustcorp.com.au</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2003</year>
+   <holder>Rusty Russell</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+ <toc></toc>
+  <chapter id="intro">
+   <title>Introduction</title>
+   <para>
+     Welcome, to Rusty's Remarkably Unreliable Guide to Kernel
+     Locking issues.  This document describes the locking systems in
+     the Linux Kernel in 2.6.
+   </para>
+   <para>
+     With the wide availability of HyperThreading, and <firstterm
+     linkend="gloss-preemption">preemption </firstterm> in the Linux
+     Kernel, everyone hacking on the kernel needs to know the
+     fundamentals of concurrency and locking for
+     <firstterm linkend="gloss-smp"><acronym>SMP</acronym></firstterm>.
+   </para>
+  </chapter>
+
+   <chapter id="races">
+    <title>The Problem With Concurrency</title>
+    <para>
+      (Skip this if you know what a Race Condition is).
+    </para>
+    <para>
+      In a normal program, you can increment a counter like so:
+    </para>
+    <programlisting>
+      very_important_count++;
+    </programlisting>
+
+    <para>
+      This is what they would expect to happen:
+    </para>
+
+    <table>
+     <title>Expected Results</title>
+
+     <tgroup cols="2" align="left">
+
+      <thead>
+       <row>
+        <entry>Instance 1</entry>
+        <entry>Instance 2</entry>
+       </row>
+      </thead>
+
+      <tbody>
+       <row>
+        <entry>read very_important_count (5)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry>add 1 (6)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry>write very_important_count (6)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>read very_important_count (6)</entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>add 1 (7)</entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>write very_important_count (7)</entry>
+       </row>
+      </tbody>
+
+     </tgroup>
+    </table>
+
+    <para>
+     This is what might happen:
+    </para>
+
+    <table>
+     <title>Possible Results</title>
+
+     <tgroup cols="2" align="left">
+      <thead>
+       <row>
+        <entry>Instance 1</entry>
+        <entry>Instance 2</entry>
+       </row>
+      </thead>
+
+      <tbody>
+       <row>
+        <entry>read very_important_count (5)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>read very_important_count (5)</entry>
+       </row>
+       <row>
+        <entry>add 1 (6)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>add 1 (6)</entry>
+       </row>
+       <row>
+        <entry>write very_important_count (6)</entry>
+        <entry></entry>
+       </row>
+       <row>
+        <entry></entry>
+        <entry>write very_important_count (6)</entry>
+       </row>
+      </tbody>
+     </tgroup>
+    </table>
+
+    <sect1 id="race-condition">
+    <title>Race Conditions and Critical Regions</title>
+    <para>
+      This overlap, where the result depends on the
+      relative timing of multiple tasks, is called a <firstterm>race condition</firstterm>.
+      The piece of code containing the concurrency issue is called a
+      <firstterm>critical region</firstterm>.  And especially since Linux starting running
+      on SMP machines, they became one of the major issues in kernel
+      design and implementation.
+    </para>
+    <para>
+      Preemption can have the same effect, even if there is only one
+      CPU: by preempting one task during the critical region, we have
+      exactly the same race condition.  In this case the thread which
+      preempts might run the critical region itself.
+    </para>
+    <para>
+      The solution is to recognize when these simultaneous accesses
+      occur, and use locks to make sure that only one instance can
+      enter the critical region at any time.  There are many
+      friendly primitives in the Linux kernel to help you do this.
+      And then there are the unfriendly primitives, but I'll pretend
+      they don't exist.
+    </para>
+    </sect1>
+  </chapter>
+
+  <chapter id="locks">
+   <title>Locking in the Linux Kernel</title>
+
+   <para>
+     If I could give you one piece of advice: never sleep with anyone
+     crazier than yourself.  But if I had to give you advice on
+     locking: <emphasis>keep it simple</emphasis>.
+   </para>
+
+   <para>
+     Be reluctant to introduce new locks.
+   </para>
+
+   <para>
+     Strangely enough, this last one is the exact reverse of my advice when
+     you <emphasis>have</emphasis> slept with someone crazier than yourself.
+     And you should think about getting a big dog.
+   </para>
+
+   <sect1 id="lock-intro">
+   <title>Two Main Types of Kernel Locks: Spinlocks and Semaphores</title>
+
+   <para>
+     There are two main types of kernel locks.  The fundamental type
+     is the spinlock 
+     (<filename class="headerfile">include/asm/spinlock.h</filename>),
+     which is a very simple single-holder lock: if you can't get the 
+     spinlock, you keep trying (spinning) until you can.  Spinlocks are 
+     very small and fast, and can be used anywhere.
+   </para>
+   <para>
+     The second type is a semaphore
+     (<filename class="headerfile">include/asm/semaphore.h</filename>): it
+     can have more than one holder at any time (the number decided at
+     initialization time), although it is most commonly used as a
+     single-holder lock (a mutex).  If you can't get a semaphore,
+     your task will put itself on the queue, and be woken up when the
+     semaphore is released.  This means the CPU will do something
+     else while you are waiting, but there are many cases when you
+     simply can't sleep (see <xref linkend="sleeping-things"/>), and so
+     have to use a spinlock instead.
+   </para>
+   <para>
+     Neither type of lock is recursive: see
+     <xref linkend="deadlock"/>.
+   </para>
+   </sect1>
+ 
+   <sect1 id="uniprocessor">
+    <title>Locks and Uniprocessor Kernels</title>
+
+    <para>
+      For kernels compiled without <symbol>CONFIG_SMP</symbol>, and
+      without <symbol>CONFIG_PREEMPT</symbol> spinlocks do not exist at
+      all.  This is an excellent design decision: when no-one else can
+      run at the same time, there is no reason to have a lock.
+    </para>
+
+    <para>
+      If the kernel is compiled without <symbol>CONFIG_SMP</symbol>,
+      but <symbol>CONFIG_PREEMPT</symbol> is set, then spinlocks
+      simply disable preemption, which is sufficient to prevent any
+      races.  For most purposes, we can think of preemption as
+      equivalent to SMP, and not worry about it separately.
+    </para>
+
+    <para>
+      You should always test your locking code with <symbol>CONFIG_SMP</symbol>
+      and <symbol>CONFIG_PREEMPT</symbol> enabled, even if you don't have an SMP test box, because it
+      will still catch some kinds of locking bugs.
+    </para>
+
+    <para>
+      Semaphores still exist, because they are required for
+      synchronization between <firstterm linkend="gloss-usercontext">user 
+      contexts</firstterm>, as we will see below.
+    </para>
+   </sect1>
+
+    <sect1 id="usercontextlocking">
+     <title>Locking Only In User Context</title>
+
+     <para>
+       If you have a data structure which is only ever accessed from
+       user context, then you can use a simple semaphore
+       (<filename>linux/asm/semaphore.h</filename>) to protect it.  This 
+       is the most trivial case: you initialize the semaphore to the number 
+       of resources available (usually 1), and call
+       <function>down_interruptible()</function> to grab the semaphore, and 
+       <function>up()</function> to release it.  There is also a 
+       <function>down()</function>, which should be avoided, because it 
+       will not return if a signal is received.
+     </para>
+
+     <para>
+       Example: <filename>linux/net/core/netfilter.c</filename> allows 
+       registration of new <function>setsockopt()</function> and 
+       <function>getsockopt()</function> calls, with
+       <function>nf_register_sockopt()</function>.  Registration and 
+       de-registration are only done on module load and unload (and boot 
+       time, where there is no concurrency), and the list of registrations 
+       is only consulted for an unknown <function>setsockopt()</function>
+       or <function>getsockopt()</function> system call.  The 
+       <varname>nf_sockopt_mutex</varname> is perfect to protect this,
+       especially since the setsockopt and getsockopt calls may well
+       sleep.
+     </para>
+   </sect1>
+
+   <sect1 id="lock-user-bh">
+    <title>Locking Between User Context and Softirqs</title>
+
+    <para>
+      If a <firstterm linkend="gloss-softirq">softirq</firstterm> shares
+      data with user context, you have two problems.  Firstly, the current 
+      user context can be interrupted by a softirq, and secondly, the
+      critical region could be entered from another CPU.  This is where
+      <function>spin_lock_bh()</function> 
+      (<filename class="headerfile">include/linux/spinlock.h</filename>) is
+      used.  It disables softirqs on that CPU, then grabs the lock.
+      <function>spin_unlock_bh()</function> does the reverse.  (The
+      '_bh' suffix is a historical reference to "Bottom Halves", the
+      old name for software interrupts.  It should really be
+      called spin_lock_softirq()' in a perfect world).
+    </para>
+
+    <para>
+      Note that you can also use <function>spin_lock_irq()</function>
+      or <function>spin_lock_irqsave()</function> here, which stop
+      hardware interrupts as well: see <xref linkend="hardirq-context"/>.
+    </para>
+
+    <para>
+      This works perfectly for <firstterm linkend="gloss-up"><acronym>UP
+      </acronym></firstterm> as well: the spin lock vanishes, and this macro 
+      simply becomes <function>local_bh_disable()</function>
+      (<filename class="headerfile">include/linux/interrupt.h</filename>), which
+      protects you from the softirq being run.
+    </para>
+   </sect1>
+
+   <sect1 id="lock-user-tasklet">
+    <title>Locking Between User Context and Tasklets</title>
+
+    <para>
+      This is exactly the same as above, because <firstterm
+      linkend="gloss-tasklet">tasklets</firstterm> are actually run
+      from a softirq.
+    </para>
+   </sect1>
+
+   <sect1 id="lock-user-timers">
+    <title>Locking Between User Context and Timers</title>
+
+    <para>
+      This, too, is exactly the same as above, because <firstterm
+      linkend="gloss-timers">timers</firstterm> are actually run from
+      a softirq.  From a locking point of view, tasklets and timers
+      are identical.
+    </para>
+   </sect1>
+
+   <sect1 id="lock-tasklets">
+    <title>Locking Between Tasklets/Timers</title>
+
+    <para>
+      Sometimes a tasklet or timer might want to share data with
+      another tasklet or timer.
+    </para>
+
+    <sect2 id="lock-tasklets-same">
+     <title>The Same Tasklet/Timer</title>
+     <para>
+       Since a tasklet is never run on two CPUs at once, you don't
+       need to worry about your tasklet being reentrant (running
+       twice at once), even on SMP.
+     </para>
+    </sect2>
+
+    <sect2 id="lock-tasklets-different">
+     <title>Different Tasklets/Timers</title>
+     <para>
+       If another tasklet/timer wants
+       to share data with your tasklet or timer , you will both need to use
+       <function>spin_lock()</function> and
+       <function>spin_unlock()</function> calls.  
+       <function>spin_lock_bh()</function> is
+       unnecessary here, as you are already in a tasklet, and
+       none will be run on the same CPU.
+     </para>
+    </sect2>
+   </sect1>
+
+   <sect1 id="lock-softirqs">
+    <title>Locking Between Softirqs</title>
+
+    <para>
+      Often a softirq might
+      want to share data with itself or a tasklet/timer.
+    </para>
+
+    <sect2 id="lock-softirqs-same">
+     <title>The Same Softirq</title>
+
+     <para>
+       The same softirq can run on the other CPUs: you can use a
+       per-CPU array (see <xref linkend="per-cpu"/>) for better
+       performance.  If you're going so far as to use a softirq,
+       you probably care about scalable performance enough
+       to justify the extra complexity.
+     </para>
+
+     <para>
+       You'll need to use <function>spin_lock()</function> and 
+       <function>spin_unlock()</function> for shared data.
+     </para>
+    </sect2>
+
+    <sect2 id="lock-softirqs-different">
+     <title>Different Softirqs</title>
+
+     <para>
+       You'll need to use <function>spin_lock()</function> and
+       <function>spin_unlock()</function> for shared data, whether it
+       be a timer, tasklet, different softirq or the same or another
+       softirq: any of them could be running on a different CPU.
+     </para>
+    </sect2>
+   </sect1>
+  </chapter>
+
+  <chapter id="hardirq-context">
+   <title>Hard IRQ Context</title>
+
+   <para>
+     Hardware interrupts usually communicate with a
+     tasklet or softirq.  Frequently this involves putting work in a
+     queue, which the softirq will take out.
+   </para>
+
+   <sect1 id="hardirq-softirq">
+    <title>Locking Between Hard IRQ and Softirqs/Tasklets</title>
+
+    <para>
+      If a hardware irq handler shares data with a softirq, you have
+      two concerns.  Firstly, the softirq processing can be
+      interrupted by a hardware interrupt, and secondly, the
+      critical region could be entered by a hardware interrupt on
+      another CPU.  This is where <function>spin_lock_irq()</function> is 
+      used.  It is defined to disable interrupts on that cpu, then grab 
+      the lock. <function>spin_unlock_irq()</function> does the reverse.
+    </para>
+
+    <para>
+      The irq handler does not to use
+      <function>spin_lock_irq()</function>, because the softirq cannot
+      run while the irq handler is running: it can use
+      <function>spin_lock()</function>, which is slightly faster.  The
+      only exception would be if a different hardware irq handler uses
+      the same lock: <function>spin_lock_irq()</function> will stop
+      that from interrupting us.
+    </para>
+
+    <para>
+      This works perfectly for UP as well: the spin lock vanishes,
+      and this macro simply becomes <function>local_irq_disable()</function>
+      (<filename class="headerfile">include/asm/smp.h</filename>), which
+      protects you from the softirq/tasklet/BH being run.
+    </para>
+
+    <para>
+      <function>spin_lock_irqsave()</function> 
+      (<filename>include/linux/spinlock.h</filename>) is a variant
+      which saves whether interrupts were on or off in a flags word,
+      which is passed to <function>spin_unlock_irqrestore()</function>.  This
+      means that the same code can be used inside an hard irq handler (where
+      interrupts are already off) and in softirqs (where the irq
+      disabling is required).
+    </para>
+
+    <para>
+      Note that softirqs (and hence tasklets and timers) are run on
+      return from hardware interrupts, so
+      <function>spin_lock_irq()</function> also stops these.  In that
+      sense, <function>spin_lock_irqsave()</function> is the most
+      general and powerful locking function.
+    </para>
+
+   </sect1>
+   <sect1 id="hardirq-hardirq">
+    <title>Locking Between Two Hard IRQ Handlers</title>
+    <para>
+      It is rare to have to share data between two IRQ handlers, but
+      if you do, <function>spin_lock_irqsave()</function> should be
+      used: it is architecture-specific whether all interrupts are
+      disabled inside irq handlers themselves.
+    </para>
+   </sect1>
+
+  </chapter>
+
+  <chapter id="cheatsheet">
+   <title>Cheat Sheet For Locking</title>
+   <para>
+     Pete Zaitcev gives the following summary:
+   </para>
+   <itemizedlist>
+      <listitem>
+	<para>
+          If you are in a process context (any syscall) and want to
+	lock other process out, use a semaphore.  You can take a semaphore
+	and sleep (<function>copy_from_user*(</function> or
+	<function>kmalloc(x,GFP_KERNEL)</function>).
+      </para>
+      </listitem>
+      <listitem>
+	<para>
+	Otherwise (== data can be touched in an interrupt), use
+	<function>spin_lock_irqsave()</function> and
+	<function>spin_unlock_irqrestore()</function>.
+	</para>
+      </listitem>
+      <listitem>
+	<para>
+	Avoid holding spinlock for more than 5 lines of code and
+	across any function call (except accessors like
+	<function>readb</function>).
+	</para>
+      </listitem>
+    </itemizedlist>
+
+   <sect1 id="minimum-lock-reqirements">
+   <title>Table of Minimum Requirements</title>
+
+   <para> The following table lists the <emphasis>minimum</emphasis>
+	locking requirements between various contexts.  In some cases,
+	the same context can only be running on one CPU at a time, so
+	no locking is required for that context (eg. a particular
+	thread can only run on one CPU at a time, but if it needs
+	shares data with another thread, locking is required).
+   </para>
+   <para>
+	Remember the advice above: you can always use
+	<function>spin_lock_irqsave()</function>, which is a superset
+	of all other spinlock primitives.
+   </para>
+   <table>
+<title>Table of Locking Requirements</title>
+<tgroup cols="11">
+<tbody>
+<row>
+<entry></entry>
+<entry>IRQ Handler A</entry>
+<entry>IRQ Handler B</entry>
+<entry>Softirq A</entry>
+<entry>Softirq B</entry>
+<entry>Tasklet A</entry>
+<entry>Tasklet B</entry>
+<entry>Timer A</entry>
+<entry>Timer B</entry>
+<entry>User Context A</entry>
+<entry>User Context B</entry>
+</row>
+
+<row>
+<entry>IRQ Handler A</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>IRQ Handler B</entry>
+<entry>spin_lock_irqsave</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>Softirq A</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+</row>
+
+<row>
+<entry>Softirq B</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+</row>
+
+<row>
+<entry>Tasklet A</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>Tasklet B</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>Timer A</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>Timer B</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>spin_lock</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>User Context A</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>None</entry>
+</row>
+
+<row>
+<entry>User Context B</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_irq</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>spin_lock_bh</entry>
+<entry>down_interruptible</entry>
+<entry>None</entry>
+</row>
+
+</tbody>
+</tgroup>
+</table>
+</sect1>
+</chapter>
+
+  <chapter id="Examples">
+   <title>Common Examples</title>
+    <para>
+Let's step through a simple example: a cache of number to name
+mappings.  The cache keeps a count of how often each of the objects is
+used, and when it gets full, throws out the least used one.
+
+    </para>
+
+   <sect1 id="examples-usercontext">
+    <title>All In User Context</title>
+    <para>
+For our first example, we assume that all operations are in user
+context (ie. from system calls), so we can sleep.  This means we can
+use a semaphore to protect the cache and all the objects within
+it.  Here's the code:
+    </para>
+
+    <programlisting>
+#include &lt;linux/list.h&gt;
+#include &lt;linux/slab.h&gt;
+#include &lt;linux/string.h&gt;
+#include &lt;asm/semaphore.h&gt;
+#include &lt;asm/errno.h&gt;
+
+struct object
+{
+        struct list_head list;
+        int id;
+        char name[32];
+        int popularity;
+};
+
+/* Protects the cache, cache_num, and the objects within it */
+static DECLARE_MUTEX(cache_lock);
+static LIST_HEAD(cache);
+static unsigned int cache_num = 0;
+#define MAX_CACHE_SIZE 10
+
+/* Must be holding cache_lock */
+static struct object *__cache_find(int id)
+{
+        struct object *i;
+
+        list_for_each_entry(i, &amp;cache, list)
+                if (i-&gt;id == id) {
+                        i-&gt;popularity++;
+                        return i;
+                }
+        return NULL;
+}
+
+/* Must be holding cache_lock */
+static void __cache_delete(struct object *obj)
+{
+        BUG_ON(!obj);
+        list_del(&amp;obj-&gt;list);
+        kfree(obj);
+        cache_num--;
+}
+
+/* Must be holding cache_lock */
+static void __cache_add(struct object *obj)
+{
+        list_add(&amp;obj-&gt;list, &amp;cache);
+        if (++cache_num > MAX_CACHE_SIZE) {
+                struct object *i, *outcast = NULL;
+                list_for_each_entry(i, &amp;cache, list) {
+                        if (!outcast || i-&gt;popularity &lt; outcast-&gt;popularity)
+                                outcast = i;
+                }
+                __cache_delete(outcast);
+        }
+}
+
+int cache_add(int id, const char *name)
+{
+        struct object *obj;
+
+        if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+                return -ENOMEM;
+
+        strlcpy(obj-&gt;name, name, sizeof(obj-&gt;name));
+        obj-&gt;id = id;
+        obj-&gt;popularity = 0;
+
+        down(&amp;cache_lock);
+        __cache_add(obj);
+        up(&amp;cache_lock);
+        return 0;
+}
+
+void cache_delete(int id)
+{
+        down(&amp;cache_lock);
+        __cache_delete(__cache_find(id));
+        up(&amp;cache_lock);
+}
+
+int cache_find(int id, char *name)
+{
+        struct object *obj;
+        int ret = -ENOENT;
+
+        down(&amp;cache_lock);
+        obj = __cache_find(id);
+        if (obj) {
+                ret = 0;
+                strcpy(name, obj-&gt;name);
+        }
+        up(&amp;cache_lock);
+        return ret;
+}
+</programlisting>
+
+    <para>
+Note that we always make sure we have the cache_lock when we add,
+delete, or look up the cache: both the cache infrastructure itself and
+the contents of the objects are protected by the lock.  In this case
+it's easy, since we copy the data for the user, and never let them
+access the objects directly.
+    </para>
+    <para>
+There is a slight (and common) optimization here: in
+<function>cache_add</function> we set up the fields of the object
+before grabbing the lock.  This is safe, as no-one else can access it
+until we put it in cache.
+    </para>
+    </sect1>
+
+   <sect1 id="examples-interrupt">
+    <title>Accessing From Interrupt Context</title>
+    <para>
+Now consider the case where <function>cache_find</function> can be
+called from interrupt context: either a hardware interrupt or a
+softirq.  An example would be a timer which deletes object from the
+cache.
+    </para>
+    <para>
+The change is shown below, in standard patch format: the
+<symbol>-</symbol> are lines which are taken away, and the
+<symbol>+</symbol> are lines which are added.
+    </para>
+<programlisting>
+--- cache.c.usercontext	2003-12-09 13:58:54.000000000 +1100
++++ cache.c.interrupt	2003-12-09 14:07:49.000000000 +1100
+@@ -12,7 +12,7 @@
+         int popularity;
+ };
+
+-static DECLARE_MUTEX(cache_lock);
++static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED;
+ static LIST_HEAD(cache);
+ static unsigned int cache_num = 0;
+ #define MAX_CACHE_SIZE 10
+@@ -55,6 +55,7 @@
+ int cache_add(int id, const char *name)
+ {
+         struct object *obj;
++        unsigned long flags;
+
+         if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+                 return -ENOMEM;
+@@ -63,30 +64,33 @@
+         obj-&gt;id = id;
+         obj-&gt;popularity = 0;
+
+-        down(&amp;cache_lock);
++        spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_add(obj);
+-        up(&amp;cache_lock);
++        spin_unlock_irqrestore(&amp;cache_lock, flags);
+         return 0;
+ }
+
+ void cache_delete(int id)
+ {
+-        down(&amp;cache_lock);
++        unsigned long flags;
++
++        spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_delete(__cache_find(id));
+-        up(&amp;cache_lock);
++        spin_unlock_irqrestore(&amp;cache_lock, flags);
+ }
+
+ int cache_find(int id, char *name)
+ {
+         struct object *obj;
+         int ret = -ENOENT;
++        unsigned long flags;
+
+-        down(&amp;cache_lock);
++        spin_lock_irqsave(&amp;cache_lock, flags);
+         obj = __cache_find(id);
+         if (obj) {
+                 ret = 0;
+                 strcpy(name, obj-&gt;name);
+         }
+-        up(&amp;cache_lock);
++        spin_unlock_irqrestore(&amp;cache_lock, flags);
+         return ret;
+ }
+</programlisting>
+
+    <para>
+Note that the <function>spin_lock_irqsave</function> will turn off
+interrupts if they are on, otherwise does nothing (if we are already
+in an interrupt handler), hence these functions are safe to call from
+any context.
+    </para>
+    <para>
+Unfortunately, <function>cache_add</function> calls
+<function>kmalloc</function> with the <symbol>GFP_KERNEL</symbol>
+flag, which is only legal in user context.  I have assumed that
+<function>cache_add</function> is still only called in user context,
+otherwise this should become a parameter to
+<function>cache_add</function>.
+    </para>
+  </sect1>
+   <sect1 id="examples-refcnt">
+    <title>Exposing Objects Outside This File</title>
+    <para>
+If our objects contained more information, it might not be sufficient
+to copy the information in and out: other parts of the code might want
+to keep pointers to these objects, for example, rather than looking up
+the id every time.  This produces two problems.
+    </para>
+    <para>
+The first problem is that we use the <symbol>cache_lock</symbol> to
+protect objects: we'd need to make this non-static so the rest of the
+code can use it.  This makes locking trickier, as it is no longer all
+in one place.
+    </para>
+    <para>
+The second problem is the lifetime problem: if another structure keeps
+a pointer to an object, it presumably expects that pointer to remain
+valid.  Unfortunately, this is only guaranteed while you hold the
+lock, otherwise someone might call <function>cache_delete</function>
+and even worse, add another object, re-using the same address.
+    </para>
+    <para>
+As there is only one lock, you can't hold it forever: no-one else would
+get any work done.
+    </para>
+    <para>
+The solution to this problem is to use a reference count: everyone who
+has a pointer to the object increases it when they first get the
+object, and drops the reference count when they're finished with it.
+Whoever drops it to zero knows it is unused, and can actually delete it.
+    </para>
+    <para>
+Here is the code:
+    </para>
+
+<programlisting>
+--- cache.c.interrupt	2003-12-09 14:25:43.000000000 +1100
++++ cache.c.refcnt	2003-12-09 14:33:05.000000000 +1100
+@@ -7,6 +7,7 @@
+ struct object
+ {
+         struct list_head list;
++        unsigned int refcnt;
+         int id;
+         char name[32];
+         int popularity;
+@@ -17,6 +18,35 @@
+ static unsigned int cache_num = 0;
+ #define MAX_CACHE_SIZE 10
+
++static void __object_put(struct object *obj)
++{
++        if (--obj-&gt;refcnt == 0)
++                kfree(obj);
++}
++
++static void __object_get(struct object *obj)
++{
++        obj-&gt;refcnt++;
++}
++
++void object_put(struct object *obj)
++{
++        unsigned long flags;
++
++        spin_lock_irqsave(&amp;cache_lock, flags);
++        __object_put(obj);
++        spin_unlock_irqrestore(&amp;cache_lock, flags);
++}
++
++void object_get(struct object *obj)
++{
++        unsigned long flags;
++
++        spin_lock_irqsave(&amp;cache_lock, flags);
++        __object_get(obj);
++        spin_unlock_irqrestore(&amp;cache_lock, flags);
++}
++
+ /* Must be holding cache_lock */
+ static struct object *__cache_find(int id)
+ {
+@@ -35,6 +65,7 @@
+ {
+         BUG_ON(!obj);
+         list_del(&amp;obj-&gt;list);
++        __object_put(obj);
+         cache_num--;
+ }
+
+@@ -63,6 +94,7 @@
+         strlcpy(obj-&gt;name, name, sizeof(obj-&gt;name));
+         obj-&gt;id = id;
+         obj-&gt;popularity = 0;
++        obj-&gt;refcnt = 1; /* The cache holds a reference */
+
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_add(obj);
+@@ -79,18 +111,15 @@
+         spin_unlock_irqrestore(&amp;cache_lock, flags);
+ }
+
+-int cache_find(int id, char *name)
++struct object *cache_find(int id)
+ {
+         struct object *obj;
+-        int ret = -ENOENT;
+         unsigned long flags;
+
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         obj = __cache_find(id);
+-        if (obj) {
+-                ret = 0;
+-                strcpy(name, obj-&gt;name);
+-        }
++        if (obj)
++                __object_get(obj);
+         spin_unlock_irqrestore(&amp;cache_lock, flags);
+-        return ret;
++        return obj;
+ }
+</programlisting>
+
+<para>
+We encapsulate the reference counting in the standard 'get' and 'put'
+functions.  Now we can return the object itself from
+<function>cache_find</function> which has the advantage that the user
+can now sleep holding the object (eg. to
+<function>copy_to_user</function> to name to userspace).
+</para>
+<para>
+The other point to note is that I said a reference should be held for
+every pointer to the object: thus the reference count is 1 when first
+inserted into the cache.  In some versions the framework does not hold
+a reference count, but they are more complicated.
+</para>
+
+   <sect2 id="examples-refcnt-atomic">
+    <title>Using Atomic Operations For The Reference Count</title>
+<para>
+In practice, <type>atomic_t</type> would usually be used for
+<structfield>refcnt</structfield>.  There are a number of atomic
+operations defined in
+
+<filename class="headerfile">include/asm/atomic.h</filename>: these are
+guaranteed to be seen atomically from all CPUs in the system, so no
+lock is required.  In this case, it is simpler than using spinlocks,
+although for anything non-trivial using spinlocks is clearer.  The
+<function>atomic_inc</function> and
+<function>atomic_dec_and_test</function> are used instead of the
+standard increment and decrement operators, and the lock is no longer
+used to protect the reference count itself.
+</para>
+
+<programlisting>
+--- cache.c.refcnt	2003-12-09 15:00:35.000000000 +1100
++++ cache.c.refcnt-atomic	2003-12-11 15:49:42.000000000 +1100
+@@ -7,7 +7,7 @@
+ struct object
+ {
+         struct list_head list;
+-        unsigned int refcnt;
++        atomic_t refcnt;
+         int id;
+         char name[32];
+         int popularity;
+@@ -18,33 +18,15 @@
+ static unsigned int cache_num = 0;
+ #define MAX_CACHE_SIZE 10
+
+-static void __object_put(struct object *obj)
+-{
+-        if (--obj-&gt;refcnt == 0)
+-                kfree(obj);
+-}
+-
+-static void __object_get(struct object *obj)
+-{
+-        obj-&gt;refcnt++;
+-}
+-
+ void object_put(struct object *obj)
+ {
+-        unsigned long flags;
+-
+-        spin_lock_irqsave(&amp;cache_lock, flags);
+-        __object_put(obj);
+-        spin_unlock_irqrestore(&amp;cache_lock, flags);
++        if (atomic_dec_and_test(&amp;obj-&gt;refcnt))
++                kfree(obj);
+ }
+
+ void object_get(struct object *obj)
+ {
+-        unsigned long flags;
+-
+-        spin_lock_irqsave(&amp;cache_lock, flags);
+-        __object_get(obj);
+-        spin_unlock_irqrestore(&amp;cache_lock, flags);
++        atomic_inc(&amp;obj-&gt;refcnt);
+ }
+
+ /* Must be holding cache_lock */
+@@ -65,7 +47,7 @@
+ {
+         BUG_ON(!obj);
+         list_del(&amp;obj-&gt;list);
+-        __object_put(obj);
++        object_put(obj);
+         cache_num--;
+ }
+
+@@ -94,7 +76,7 @@
+         strlcpy(obj-&gt;name, name, sizeof(obj-&gt;name));
+         obj-&gt;id = id;
+         obj-&gt;popularity = 0;
+-        obj-&gt;refcnt = 1; /* The cache holds a reference */
++        atomic_set(&amp;obj-&gt;refcnt, 1); /* The cache holds a reference */
+
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_add(obj);
+@@ -119,7 +101,7 @@
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         obj = __cache_find(id);
+         if (obj)
+-                __object_get(obj);
++                object_get(obj);
+         spin_unlock_irqrestore(&amp;cache_lock, flags);
+         return obj;
+ }
+</programlisting>
+</sect2>
+</sect1>
+
+   <sect1 id="examples-lock-per-obj">
+    <title>Protecting The Objects Themselves</title>
+    <para>
+In these examples, we assumed that the objects (except the reference
+counts) never changed once they are created.  If we wanted to allow
+the name to change, there are three possibilities:
+    </para>
+    <itemizedlist>
+      <listitem>
+	<para>
+You can make <symbol>cache_lock</symbol> non-static, and tell people
+to grab that lock before changing the name in any object.
+        </para>
+      </listitem>
+      <listitem>
+        <para>
+You can provide a <function>cache_obj_rename</function> which grabs
+this lock and changes the name for the caller, and tell everyone to
+use that function.
+        </para>
+      </listitem>
+      <listitem>
+        <para>
+You can make the <symbol>cache_lock</symbol> protect only the cache
+itself, and use another lock to protect the name.
+        </para>
+      </listitem>
+    </itemizedlist>
+
+      <para>
+Theoretically, you can make the locks as fine-grained as one lock for
+every field, for every object.  In practice, the most common variants
+are:
+</para>
+    <itemizedlist>
+      <listitem>
+	<para>
+One lock which protects the infrastructure (the <symbol>cache</symbol>
+list in this example) and all the objects.  This is what we have done
+so far.
+	</para>
+      </listitem>
+      <listitem>
+        <para>
+One lock which protects the infrastructure (including the list
+pointers inside the objects), and one lock inside the object which
+protects the rest of that object.
+        </para>
+      </listitem>
+      <listitem>
+        <para>
+Multiple locks to protect the infrastructure (eg. one lock per hash
+chain), possibly with a separate per-object lock.
+        </para>
+      </listitem>
+    </itemizedlist>
+
+<para>
+Here is the "lock-per-object" implementation:
+</para>
+<programlisting>
+--- cache.c.refcnt-atomic	2003-12-11 15:50:54.000000000 +1100
++++ cache.c.perobjectlock	2003-12-11 17:15:03.000000000 +1100
+@@ -6,11 +6,17 @@
+
+ struct object
+ {
++        /* These two protected by cache_lock. */
+         struct list_head list;
++        int popularity;
++
+         atomic_t refcnt;
++
++        /* Doesn't change once created. */
+         int id;
++
++        spinlock_t lock; /* Protects the name */
+         char name[32];
+-        int popularity;
+ };
+
+ static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED;
+@@ -77,6 +84,7 @@
+         obj-&gt;id = id;
+         obj-&gt;popularity = 0;
+         atomic_set(&amp;obj-&gt;refcnt, 1); /* The cache holds a reference */
++        spin_lock_init(&amp;obj-&gt;lock);
+
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_add(obj);
+</programlisting>
+
+<para>
+Note that I decide that the <structfield>popularity</structfield>
+count should be protected by the <symbol>cache_lock</symbol> rather
+than the per-object lock: this is because it (like the
+<structname>struct list_head</structname> inside the object) is
+logically part of the infrastructure.  This way, I don't need to grab
+the lock of every object in <function>__cache_add</function> when
+seeking the least popular.
+</para>
+
+<para>
+I also decided that the <structfield>id</structfield> member is
+unchangeable, so I don't need to grab each object lock in
+<function>__cache_find()</function> to examine the
+<structfield>id</structfield>: the object lock is only used by a
+caller who wants to read or write the <structfield>name</structfield>
+field.
+</para>
+
+<para>
+Note also that I added a comment describing what data was protected by
+which locks.  This is extremely important, as it describes the runtime
+behavior of the code, and can be hard to gain from just reading.  And
+as Alan Cox says, <quote>Lock data, not code</quote>.
+</para>
+</sect1>
+</chapter>
+
+   <chapter id="common-problems">
+    <title>Common Problems</title>
+    <sect1 id="deadlock">
+    <title>Deadlock: Simple and Advanced</title>
+
+    <para>
+      There is a coding bug where a piece of code tries to grab a
+      spinlock twice: it will spin forever, waiting for the lock to
+      be released (spinlocks, rwlocks and semaphores are not
+      recursive in Linux).  This is trivial to diagnose: not a
+      stay-up-five-nights-talk-to-fluffy-code-bunnies kind of
+      problem.
+    </para>
+
+    <para>
+      For a slightly more complex case, imagine you have a region
+      shared by a softirq and user context.  If you use a
+      <function>spin_lock()</function> call to protect it, it is 
+      possible that the user context will be interrupted by the softirq
+      while it holds the lock, and the softirq will then spin
+      forever trying to get the same lock.
+    </para>
+
+    <para>
+      Both of these are called deadlock, and as shown above, it can
+      occur even with a single CPU (although not on UP compiles,
+      since spinlocks vanish on kernel compiles with 
+      <symbol>CONFIG_SMP</symbol>=n. You'll still get data corruption 
+      in the second example).
+    </para>
+
+    <para>
+      This complete lockup is easy to diagnose: on SMP boxes the
+      watchdog timer or compiling with <symbol>DEBUG_SPINLOCKS</symbol> set
+      (<filename>include/linux/spinlock.h</filename>) will show this up 
+      immediately when it happens.
+    </para>
+
+    <para>
+      A more complex problem is the so-called 'deadly embrace',
+      involving two or more locks.  Say you have a hash table: each
+      entry in the table is a spinlock, and a chain of hashed
+      objects.  Inside a softirq handler, you sometimes want to
+      alter an object from one place in the hash to another: you
+      grab the spinlock of the old hash chain and the spinlock of
+      the new hash chain, and delete the object from the old one,
+      and insert it in the new one.
+    </para>
+
+    <para>
+      There are two problems here.  First, if your code ever
+      tries to move the object to the same chain, it will deadlock
+      with itself as it tries to lock it twice.  Secondly, if the
+      same softirq on another CPU is trying to move another object
+      in the reverse direction, the following could happen:
+    </para>
+
+    <table>
+     <title>Consequences</title>
+
+     <tgroup cols="2" align="left">
+
+      <thead>
+       <row>
+        <entry>CPU 1</entry>
+        <entry>CPU 2</entry>
+       </row>
+      </thead>
+
+      <tbody>
+       <row>
+        <entry>Grab lock A -&gt; OK</entry>
+        <entry>Grab lock B -&gt; OK</entry>
+       </row>
+       <row>
+        <entry>Grab lock B -&gt; spin</entry>
+        <entry>Grab lock A -&gt; spin</entry>
+       </row>
+      </tbody>
+     </tgroup>
+    </table>
+
+    <para>
+      The two CPUs will spin forever, waiting for the other to give up
+      their lock.  It will look, smell, and feel like a crash.
+    </para>
+    </sect1>
+
+    <sect1 id="techs-deadlock-prevent">
+     <title>Preventing Deadlock</title>
+
+     <para>
+       Textbooks will tell you that if you always lock in the same
+       order, you will never get this kind of deadlock.  Practice
+       will tell you that this approach doesn't scale: when I
+       create a new lock, I don't understand enough of the kernel
+       to figure out where in the 5000 lock hierarchy it will fit.
+     </para>
+
+     <para>
+       The best locks are encapsulated: they never get exposed in
+       headers, and are never held around calls to non-trivial
+       functions outside the same file.  You can read through this
+       code and see that it will never deadlock, because it never
+       tries to grab another lock while it has that one.  People
+       using your code don't even need to know you are using a
+       lock.
+     </para>
+
+     <para>
+       A classic problem here is when you provide callbacks or
+       hooks: if you call these with the lock held, you risk simple
+       deadlock, or a deadly embrace (who knows what the callback
+       will do?).  Remember, the other programmers are out to get
+       you, so don't do this.
+     </para>
+
+    <sect2 id="techs-deadlock-overprevent">
+     <title>Overzealous Prevention Of Deadlocks</title>
+
+     <para>
+       Deadlocks are problematic, but not as bad as data
+       corruption.  Code which grabs a read lock, searches a list,
+       fails to find what it wants, drops the read lock, grabs a
+       write lock and inserts the object has a race condition.
+     </para>
+
+     <para>
+       If you don't see why, please stay the fuck away from my code.
+     </para>
+    </sect2>
+    </sect1>
+
+   <sect1 id="racing-timers">
+    <title>Racing Timers: A Kernel Pastime</title>
+
+    <para>
+      Timers can produce their own special problems with races.
+      Consider a collection of objects (list, hash, etc) where each
+      object has a timer which is due to destroy it.
+    </para>
+
+    <para>
+      If you want to destroy the entire collection (say on module
+      removal), you might do the following:
+    </para>
+
+    <programlisting>
+        /* THIS CODE BAD BAD BAD BAD: IF IT WAS ANY WORSE IT WOULD USE
+           HUNGARIAN NOTATION */
+        spin_lock_bh(&amp;list_lock);
+
+        while (list) {
+                struct foo *next = list-&gt;next;
+                del_timer(&amp;list-&gt;timer);
+                kfree(list);
+                list = next;
+        }
+
+        spin_unlock_bh(&amp;list_lock);
+    </programlisting>
+
+    <para>
+      Sooner or later, this will crash on SMP, because a timer can
+      have just gone off before the <function>spin_lock_bh()</function>,
+      and it will only get the lock after we
+      <function>spin_unlock_bh()</function>, and then try to free
+      the element (which has already been freed!).
+    </para>
+
+    <para>
+      This can be avoided by checking the result of
+      <function>del_timer()</function>: if it returns
+      <returnvalue>1</returnvalue>, the timer has been deleted.
+      If <returnvalue>0</returnvalue>, it means (in this
+      case) that it is currently running, so we can do:
+    </para>
+
+    <programlisting>
+        retry:
+                spin_lock_bh(&amp;list_lock);
+
+                while (list) {
+                        struct foo *next = list-&gt;next;
+                        if (!del_timer(&amp;list-&gt;timer)) {
+                                /* Give timer a chance to delete this */
+                                spin_unlock_bh(&amp;list_lock);
+                                goto retry;
+                        }
+                        kfree(list);
+                        list = next;
+                }
+
+                spin_unlock_bh(&amp;list_lock);
+    </programlisting>
+
+    <para>
+      Another common problem is deleting timers which restart
+      themselves (by calling <function>add_timer()</function> at the end
+      of their timer function).  Because this is a fairly common case
+      which is prone to races, you should use <function>del_timer_sync()</function>
+      (<filename class="headerfile">include/linux/timer.h</filename>)
+      to handle this case.  It returns the number of times the timer
+      had to be deleted before we finally stopped it from adding itself back
+      in.
+    </para>
+   </sect1>
+
+  </chapter>
+
+ <chapter id="Efficiency">
+    <title>Locking Speed</title>
+
+    <para>
+There are three main things to worry about when considering speed of
+some code which does locking.  First is concurrency: how many things
+are going to be waiting while someone else is holding a lock.  Second
+is the time taken to actually acquire and release an uncontended lock.
+Third is using fewer, or smarter locks.  I'm assuming that the lock is
+used fairly often: otherwise, you wouldn't be concerned about
+efficiency.
+</para>
+    <para>
+Concurrency depends on how long the lock is usually held: you should
+hold the lock for as long as needed, but no longer.  In the cache
+example, we always create the object without the lock held, and then
+grab the lock only when we are ready to insert it in the list.
+</para>
+    <para>
+Acquisition times depend on how much damage the lock operations do to
+the pipeline (pipeline stalls) and how likely it is that this CPU was
+the last one to grab the lock (ie. is the lock cache-hot for this
+CPU): on a machine with more CPUs, this likelihood drops fast.
+Consider a 700MHz Intel Pentium III: an instruction takes about 0.7ns,
+an atomic increment takes about 58ns, a lock which is cache-hot on
+this CPU takes 160ns, and a cacheline transfer from another CPU takes
+an additional 170 to 360ns.  (These figures from Paul McKenney's
+<ulink url="http://www.linuxjournal.com/article.php?sid=6993"> Linux
+Journal RCU article</ulink>).
+</para>
+    <para>
+These two aims conflict: holding a lock for a short time might be done
+by splitting locks into parts (such as in our final per-object-lock
+example), but this increases the number of lock acquisitions, and the
+results are often slower than having a single lock.  This is another
+reason to advocate locking simplicity.
+</para>
+    <para>
+The third concern is addressed below: there are some methods to reduce
+the amount of locking which needs to be done.
+</para>
+
+  <sect1 id="efficiency-rwlocks">
+   <title>Read/Write Lock Variants</title>
+
+   <para>
+      Both spinlocks and semaphores have read/write variants:
+      <type>rwlock_t</type> and <structname>struct rw_semaphore</structname>.
+      These divide users into two classes: the readers and the writers.  If
+      you are only reading the data, you can get a read lock, but to write to
+      the data you need the write lock.  Many people can hold a read lock,
+      but a writer must be sole holder.
+    </para>
+
+   <para>
+      If your code divides neatly along reader/writer lines (as our
+      cache code does), and the lock is held by readers for
+      significant lengths of time, using these locks can help.  They
+      are slightly slower than the normal locks though, so in practice
+      <type>rwlock_t</type> is not usually worthwhile.
+    </para>
+   </sect1>
+
+   <sect1 id="efficiency-read-copy-update">
+    <title>Avoiding Locks: Read Copy Update</title>
+
+    <para>
+      There is a special method of read/write locking called Read Copy
+      Update.  Using RCU, the readers can avoid taking a lock
+      altogether: as we expect our cache to be read more often than
+      updated (otherwise the cache is a waste of time), it is a
+      candidate for this optimization.
+    </para>
+
+    <para>
+      How do we get rid of read locks?  Getting rid of read locks
+      means that writers may be changing the list underneath the
+      readers.  That is actually quite simple: we can read a linked
+      list while an element is being added if the writer adds the
+      element very carefully.  For example, adding
+      <symbol>new</symbol> to a single linked list called
+      <symbol>list</symbol>:
+    </para>
+
+    <programlisting>
+        new-&gt;next = list-&gt;next;
+        wmb();
+        list-&gt;next = new;
+    </programlisting>
+
+    <para>
+      The <function>wmb()</function> is a write memory barrier.  It
+      ensures that the first operation (setting the new element's
+      <symbol>next</symbol> pointer) is complete and will be seen by
+      all CPUs, before the second operation is (putting the new
+      element into the list).  This is important, since modern
+      compilers and modern CPUs can both reorder instructions unless
+      told otherwise: we want a reader to either not see the new
+      element at all, or see the new element with the
+      <symbol>next</symbol> pointer correctly pointing at the rest of
+      the list.
+    </para>
+    <para>
+      Fortunately, there is a function to do this for standard
+      <structname>struct list_head</structname> lists:
+      <function>list_add_rcu()</function>
+      (<filename>include/linux/list.h</filename>).
+    </para>
+    <para>
+      Removing an element from the list is even simpler: we replace
+      the pointer to the old element with a pointer to its successor,
+      and readers will either see it, or skip over it.
+    </para>
+    <programlisting>
+        list-&gt;next = old-&gt;next;
+    </programlisting>
+    <para>
+      There is <function>list_del_rcu()</function>
+      (<filename>include/linux/list.h</filename>) which does this (the
+      normal version poisons the old object, which we don't want).
+    </para>
+    <para>
+      The reader must also be careful: some CPUs can look through the
+      <symbol>next</symbol> pointer to start reading the contents of
+      the next element early, but don't realize that the pre-fetched
+      contents is wrong when the <symbol>next</symbol> pointer changes
+      underneath them.  Once again, there is a
+      <function>list_for_each_entry_rcu()</function>
+      (<filename>include/linux/list.h</filename>) to help you.  Of
+      course, writers can just use
+      <function>list_for_each_entry()</function>, since there cannot
+      be two simultaneous writers.
+    </para>
+    <para>
+      Our final dilemma is this: when can we actually destroy the
+      removed element?  Remember, a reader might be stepping through
+      this element in the list right now: it we free this element and
+      the <symbol>next</symbol> pointer changes, the reader will jump
+      off into garbage and crash.  We need to wait until we know that
+      all the readers who were traversing the list when we deleted the
+      element are finished.  We use <function>call_rcu()</function> to
+      register a callback which will actually destroy the object once
+      the readers are finished.
+    </para>
+    <para>
+      But how does Read Copy Update know when the readers are
+      finished?  The method is this: firstly, the readers always
+      traverse the list inside
+      <function>rcu_read_lock()</function>/<function>rcu_read_unlock()</function>
+      pairs: these simply disable preemption so the reader won't go to
+      sleep while reading the list.
+    </para>
+    <para>
+      RCU then waits until every other CPU has slept at least once:
+      since readers cannot sleep, we know that any readers which were
+      traversing the list during the deletion are finished, and the
+      callback is triggered.  The real Read Copy Update code is a
+      little more optimized than this, but this is the fundamental
+      idea.
+    </para>
+
+<programlisting>
+--- cache.c.perobjectlock	2003-12-11 17:15:03.000000000 +1100
++++ cache.c.rcupdate	2003-12-11 17:55:14.000000000 +1100
+@@ -1,15 +1,18 @@
+ #include &lt;linux/list.h&gt;
+ #include &lt;linux/slab.h&gt;
+ #include &lt;linux/string.h&gt;
++#include &lt;linux/rcupdate.h&gt;
+ #include &lt;asm/semaphore.h&gt;
+ #include &lt;asm/errno.h&gt;
+
+ struct object
+ {
+-        /* These two protected by cache_lock. */
++        /* This is protected by RCU */
+         struct list_head list;
+         int popularity;
+
++        struct rcu_head rcu;
++
+         atomic_t refcnt;
+
+         /* Doesn't change once created. */
+@@ -40,7 +43,7 @@
+ {
+         struct object *i;
+
+-        list_for_each_entry(i, &amp;cache, list) {
++        list_for_each_entry_rcu(i, &amp;cache, list) {
+                 if (i-&gt;id == id) {
+                         i-&gt;popularity++;
+                         return i;
+@@ -49,19 +52,25 @@
+         return NULL;
+ }
+
++/* Final discard done once we know no readers are looking. */
++static void cache_delete_rcu(void *arg)
++{
++        object_put(arg);
++}
++
+ /* Must be holding cache_lock */
+ static void __cache_delete(struct object *obj)
+ {
+         BUG_ON(!obj);
+-        list_del(&amp;obj-&gt;list);
+-        object_put(obj);
++        list_del_rcu(&amp;obj-&gt;list);
+         cache_num--;
++        call_rcu(&amp;obj-&gt;rcu, cache_delete_rcu, obj);
+ }
+
+ /* Must be holding cache_lock */
+ static void __cache_add(struct object *obj)
+ {
+-        list_add(&amp;obj-&gt;list, &amp;cache);
++        list_add_rcu(&amp;obj-&gt;list, &amp;cache);
+         if (++cache_num > MAX_CACHE_SIZE) {
+                 struct object *i, *outcast = NULL;
+                 list_for_each_entry(i, &amp;cache, list) {
+@@ -85,6 +94,7 @@
+         obj-&gt;popularity = 0;
+         atomic_set(&amp;obj-&gt;refcnt, 1); /* The cache holds a reference */
+         spin_lock_init(&amp;obj-&gt;lock);
++        INIT_RCU_HEAD(&amp;obj-&gt;rcu);
+
+         spin_lock_irqsave(&amp;cache_lock, flags);
+         __cache_add(obj);
+@@ -104,12 +114,11 @@
+ struct object *cache_find(int id)
+ {
+         struct object *obj;
+-        unsigned long flags;
+
+-        spin_lock_irqsave(&amp;cache_lock, flags);
++        rcu_read_lock();
+         obj = __cache_find(id);
+         if (obj)
+                 object_get(obj);
+-        spin_unlock_irqrestore(&amp;cache_lock, flags);
++        rcu_read_unlock();
+         return obj;
+ }
+</programlisting>
+
+<para>
+Note that the reader will alter the
+<structfield>popularity</structfield> member in
+<function>__cache_find()</function>, and now it doesn't hold a lock.
+One solution would be to make it an <type>atomic_t</type>, but for
+this usage, we don't really care about races: an approximate result is
+good enough, so I didn't change it.
+</para>
+
+<para>
+The result is that <function>cache_find()</function> requires no
+synchronization with any other functions, so is almost as fast on SMP
+as it would be on UP.
+</para>
+
+<para>
+There is a furthur optimization possible here: remember our original
+cache code, where there were no reference counts and the caller simply
+held the lock whenever using the object?  This is still possible: if
+you hold the lock, noone can delete the object, so you don't need to
+get and put the reference count.
+</para>
+
+<para>
+Now, because the 'read lock' in RCU is simply disabling preemption, a
+caller which always has preemption disabled between calling
+<function>cache_find()</function> and
+<function>object_put()</function> does not need to actually get and
+put the reference count: we could expose
+<function>__cache_find()</function> by making it non-static, and
+such callers could simply call that.
+</para>
+<para>
+The benefit here is that the reference count is not written to: the
+object is not altered in any way, which is much faster on SMP
+machines due to caching.
+</para>
+  </sect1>
+
+   <sect1 id="per-cpu">
+    <title>Per-CPU Data</title>
+
+    <para>
+      Another technique for avoiding locking which is used fairly
+      widely is to duplicate information for each CPU.  For example,
+      if you wanted to keep a count of a common condition, you could
+      use a spin lock and a single counter.  Nice and simple.
+    </para>
+
+    <para>
+      If that was too slow (it's usually not, but if you've got a
+      really big machine to test on and can show that it is), you
+      could instead use a counter for each CPU, then none of them need
+      an exclusive lock.  See <function>DEFINE_PER_CPU()</function>,
+      <function>get_cpu_var()</function> and
+      <function>put_cpu_var()</function>
+      (<filename class="headerfile">include/linux/percpu.h</filename>).
+    </para>
+
+    <para>
+      Of particular use for simple per-cpu counters is the
+      <type>local_t</type> type, and the
+      <function>cpu_local_inc()</function> and related functions,
+      which are more efficient than simple code on some architectures
+      (<filename class="headerfile">include/asm/local.h</filename>).
+    </para>
+
+    <para>
+      Note that there is no simple, reliable way of getting an exact
+      value of such a counter, without introducing more locks.  This
+      is not a problem for some uses.
+    </para>
+   </sect1>
+
+   <sect1 id="mostly-hardirq">
+    <title>Data Which Mostly Used By An IRQ Handler</title>
+
+    <para>
+      If data is always accessed from within the same IRQ handler, you
+      don't need a lock at all: the kernel already guarantees that the
+      irq handler will not run simultaneously on multiple CPUs.
+    </para>
+    <para>
+      Manfred Spraul points out that you can still do this, even if
+      the data is very occasionally accessed in user context or
+      softirqs/tasklets.  The irq handler doesn't use a lock, and
+      all other accesses are done as so:
+    </para>
+
+<programlisting>
+	spin_lock(&amp;lock);
+	disable_irq(irq);
+	...
+	enable_irq(irq);
+	spin_unlock(&amp;lock);
+</programlisting>
+    <para>
+      The <function>disable_irq()</function> prevents the irq handler
+      from running (and waits for it to finish if it's currently
+      running on other CPUs).  The spinlock prevents any other
+      accesses happening at the same time.  Naturally, this is slower
+      than just a <function>spin_lock_irq()</function> call, so it
+      only makes sense if this type of access happens extremely
+      rarely.
+    </para>
+   </sect1>
+  </chapter>
+
+ <chapter id="sleeping-things">
+    <title>What Functions Are Safe To Call From Interrupts?</title>
+
+    <para>
+      Many functions in the kernel sleep (ie. call schedule())
+      directly or indirectly: you can never call them while holding a
+      spinlock, or with preemption disabled.  This also means you need
+      to be in user context: calling them from an interrupt is illegal.
+    </para>
+
+   <sect1 id="sleeping">
+    <title>Some Functions Which Sleep</title>
+
+    <para>
+      The most common ones are listed below, but you usually have to
+      read the code to find out if other calls are safe.  If everyone
+      else who calls it can sleep, you probably need to be able to
+      sleep, too.  In particular, registration and deregistration
+      functions usually expect to be called from user context, and can
+      sleep.
+    </para>
+
+    <itemizedlist>
+     <listitem>
+      <para>
+        Accesses to 
+        <firstterm linkend="gloss-userspace">userspace</firstterm>:
+      </para>
+      <itemizedlist>
+       <listitem>
+        <para>
+          <function>copy_from_user()</function>
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+          <function>copy_to_user()</function>
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+          <function>get_user()</function>
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+          <function> put_user()</function>
+        </para>
+       </listitem>
+      </itemizedlist>
+     </listitem>
+
+     <listitem>
+      <para>
+        <function>kmalloc(GFP_KERNEL)</function>
+      </para>
+     </listitem>
+
+     <listitem>
+      <para>
+      <function>down_interruptible()</function> and
+      <function>down()</function>
+      </para>
+      <para>
+       There is a <function>down_trylock()</function> which can be
+       used inside interrupt context, as it will not sleep.
+       <function>up()</function> will also never sleep.
+      </para>
+     </listitem>
+    </itemizedlist>
+   </sect1>
+
+   <sect1 id="dont-sleep">
+    <title>Some Functions Which Don't Sleep</title>
+
+    <para>
+     Some functions are safe to call from any context, or holding
+     almost any lock.
+    </para>
+
+    <itemizedlist>
+     <listitem>
+      <para>
+	<function>printk()</function>
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+        <function>kfree()</function>
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+	<function>add_timer()</function> and <function>del_timer()</function>
+      </para>
+     </listitem>
+    </itemizedlist>
+   </sect1>
+  </chapter>
+
+  <chapter id="references">
+   <title>Further reading</title>
+
+   <itemizedlist>
+    <listitem>
+     <para>
+       <filename>Documentation/spinlocks.txt</filename>: 
+       Linus Torvalds' spinlocking tutorial in the kernel sources.
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
+       Unix Systems for Modern Architectures: Symmetric
+       Multiprocessing and Caching for Kernel Programmers:
+     </para>
+
+     <para>
+       Curt Schimmel's very good introduction to kernel level
+       locking (not written for Linux, but nearly everything
+       applies).  The book is expensive, but really worth every
+       penny to understand SMP locking. [ISBN: 0201633388]
+     </para>
+    </listitem>
+   </itemizedlist>
+  </chapter>
+
+  <chapter id="thanks">
+    <title>Thanks</title>
+
+    <para>
+      Thanks to Telsa Gwynne for DocBooking, neatening and adding
+      style.
+    </para>
+
+    <para>
+      Thanks to Martin Pool, Philipp Rumpf, Stephen Rothwell, Paul
+      Mackerras, Ruedi Aschwanden, Alan Cox, Manfred Spraul, Tim
+      Waugh, Pete Zaitcev, James Morris, Robert Love, Paul McKenney,
+      John Ashby for proofreading, correcting, flaming, commenting.
+    </para>
+
+    <para>
+      Thanks to the cabal for having no influence on this document.
+    </para>
+  </chapter>
+
+  <glossary id="glossary">
+   <title>Glossary</title>
+
+   <glossentry id="gloss-preemption">
+    <glossterm>preemption</glossterm>
+     <glossdef>
+      <para>
+        Prior to 2.5, or when <symbol>CONFIG_PREEMPT</symbol> is
+        unset, processes in user context inside the kernel would not
+        preempt each other (ie. you had that CPU until you have it up,
+        except for interrupts).  With the addition of
+        <symbol>CONFIG_PREEMPT</symbol> in 2.5.4, this changed: when
+        in user context, higher priority tasks can "cut in": spinlocks
+        were changed to disable preemption, even on UP.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-bh">
+    <glossterm>bh</glossterm>
+     <glossdef>
+      <para>
+        Bottom Half: for historical reasons, functions with
+        '_bh' in them often now refer to any software interrupt, e.g.
+        <function>spin_lock_bh()</function> blocks any software interrupt 
+        on the current CPU.  Bottom halves are deprecated, and will 
+        eventually be replaced by tasklets.  Only one bottom half will be 
+        running at any time.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-hwinterrupt">
+    <glossterm>Hardware Interrupt / Hardware IRQ</glossterm>
+    <glossdef>
+     <para>
+       Hardware interrupt request.  <function>in_irq()</function> returns 
+       <returnvalue>true</returnvalue> in a hardware interrupt handler.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-interruptcontext">
+    <glossterm>Interrupt Context</glossterm>
+    <glossdef>
+     <para>
+       Not user context: processing a hardware irq or software irq.
+       Indicated by the <function>in_interrupt()</function> macro 
+       returning <returnvalue>true</returnvalue>.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-smp">
+    <glossterm><acronym>SMP</acronym></glossterm>
+    <glossdef>
+     <para>
+       Symmetric Multi-Processor: kernels compiled for multiple-CPU
+       machines.  (CONFIG_SMP=y).
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-softirq">
+    <glossterm>Software Interrupt / softirq</glossterm>
+    <glossdef>
+     <para>
+       Software interrupt handler.  <function>in_irq()</function> returns
+       <returnvalue>false</returnvalue>; <function>in_softirq()</function>
+       returns <returnvalue>true</returnvalue>.  Tasklets and softirqs
+	both fall into the category of 'software interrupts'.
+     </para>
+     <para>
+       Strictly speaking a softirq is one of up to 32 enumerated software
+       interrupts which can run on multiple CPUs at once.
+       Sometimes used to refer to tasklets as
+       well (ie. all software interrupts).
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-tasklet">
+    <glossterm>tasklet</glossterm>
+    <glossdef>
+     <para>
+       A dynamically-registrable software interrupt,
+       which is guaranteed to only run on one CPU at a time.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-timers">
+    <glossterm>timer</glossterm>
+    <glossdef>
+     <para>
+       A dynamically-registrable software interrupt, which is run at
+       (or close to) a given time.  When running, it is just like a
+       tasklet (in fact, they are called from the TIMER_SOFTIRQ).
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-up">
+    <glossterm><acronym>UP</acronym></glossterm>
+    <glossdef>
+     <para>
+       Uni-Processor: Non-SMP.  (CONFIG_SMP=n).
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-usercontext">
+    <glossterm>User Context</glossterm>
+    <glossdef>
+     <para>
+       The kernel executing on behalf of a particular process (ie. a
+       system call or trap) or kernel thread.  You can tell which
+       process with the <symbol>current</symbol> macro.)  Not to
+       be confused with userspace.  Can be interrupted by software or
+       hardware interrupts.
+     </para>
+    </glossdef>
+   </glossentry>
+
+   <glossentry id="gloss-userspace">
+    <glossterm>Userspace</glossterm>
+    <glossdef>
+     <para>
+       A process executing its own code outside the kernel.
+     </para>
+    </glossdef>
+   </glossentry>      
+
+  </glossary>
+</book>
+
diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl
new file mode 100644
index 000000000000..cf2fce7707da
--- /dev/null
+++ b/Documentation/DocBook/libata.tmpl
@@ -0,0 +1,282 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="libataDevGuide">
+ <bookinfo>
+  <title>libATA Developer's Guide</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Jeff</firstname>
+    <surname>Garzik</surname>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2003</year>
+   <holder>Jeff Garzik</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+   The contents of this file are subject to the Open
+   Software License version 1.1 that can be found at
+   <ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein
+   by reference.
+   </para>
+
+   <para>
+   Alternatively, the contents of this file may be used under the terms
+   of the GNU General Public License version 2 (the "GPL") as distributed
+   in the kernel source COPYING file, in which case the provisions of
+   the GPL are applicable instead of the above.  If you wish to allow
+   the use of your version of this file only under the terms of the
+   GPL and not to allow others to use your version of this file under
+   the OSL, indicate your decision by deleting the provisions above and
+   replace them with the notice and other provisions required by the GPL.
+   If you do not delete the provisions above, a recipient may use your
+   version of this file under either the OSL or the GPL.
+   </para>
+
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="libataThanks">
+     <title>Thanks</title>
+  <para>
+  The bulk of the ATA knowledge comes thanks to long conversations with
+  Andre Hedrick (www.linux-ide.org).
+  </para>
+  <para>
+  Thanks to Alan Cox for pointing out similarities 
+  between SATA and SCSI, and in general for motivation to hack on
+  libata.
+  </para>
+  <para>
+  libata's device detection
+  method, ata_pio_devchk, and in general all the early probing was
+  based on extensive study of Hale Landis's probe/reset code in his
+  ATADRVR driver (www.ata-atapi.com).
+  </para>
+  </chapter>
+
+  <chapter id="libataDriverApi">
+     <title>libata Driver API</title>
+     <sect1>
+        <title>struct ata_port_operations</title>
+
+	<programlisting>
+void (*port_disable) (struct ata_port *);
+	</programlisting>
+
+	<para>
+	Called from ata_bus_probe() and ata_bus_reset() error paths,
+	as well as when unregistering from the SCSI module (rmmod, hot
+	unplug).
+	</para>
+
+	<programlisting>
+void (*dev_config) (struct ata_port *, struct ata_device *);
+	</programlisting>
+
+	<para>
+	Called after IDENTIFY [PACKET] DEVICE is issued to each device
+	found.  Typically used to apply device-specific fixups prior to
+	issue of SET FEATURES - XFER MODE, and prior to operation.
+	</para>
+
+	<programlisting>
+void (*set_piomode) (struct ata_port *, struct ata_device *);
+void (*set_dmamode) (struct ata_port *, struct ata_device *);
+void (*post_set_mode) (struct ata_port *ap);
+	</programlisting>
+
+	<para>
+	Hooks called prior to the issue of SET FEATURES - XFER MODE
+	command.  dev->pio_mode is guaranteed to be valid when
+	->set_piomode() is called, and dev->dma_mode is guaranteed to be
+	valid when ->set_dmamode() is called.  ->post_set_mode() is
+	called unconditionally, after the SET FEATURES - XFER MODE
+	command completes successfully.
+	</para>
+
+	<para>
+	->set_piomode() is always called (if present), but
+	->set_dma_mode() is only called if DMA is possible.
+	</para>
+
+	<programlisting>
+void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
+void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
+	</programlisting>
+
+	<para>
+	->tf_load() is called to load the given taskfile into hardware
+	registers / DMA buffers.  ->tf_read() is called to read the
+	hardware registers / DMA buffers, to obtain the current set of
+	taskfile register values.
+	</para>
+
+	<programlisting>
+void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
+	</programlisting>
+
+	<para>
+	causes an ATA command, previously loaded with
+	->tf_load(), to be initiated in hardware.
+	</para>
+
+	<programlisting>
+u8   (*check_status)(struct ata_port *ap);
+void (*dev_select)(struct ata_port *ap, unsigned int device);
+	</programlisting>
+
+	<para>
+	Reads the Status ATA shadow register from hardware.  On some
+	hardware, this has the side effect of clearing the interrupt
+	condition.
+	</para>
+
+	<programlisting>
+void (*dev_select)(struct ata_port *ap, unsigned int device);
+	</programlisting>
+
+	<para>
+	Issues the low-level hardware command(s) that causes one of N
+	hardware devices to be considered 'selected' (active and
+	available for use) on the ATA bus.
+	</para>
+
+	<programlisting>
+void (*phy_reset) (struct ata_port *ap);
+	</programlisting>
+
+	<para>
+	The very first step in the probe phase.  Actions vary depending
+	on the bus type, typically.  After waking up the device and probing
+	for device presence (PATA and SATA), typically a soft reset
+	(SRST) will be performed.  Drivers typically use the helper
+	functions ata_bus_reset() or sata_phy_reset() for this hook.
+	</para>
+
+	<programlisting>
+void (*bmdma_setup) (struct ata_queued_cmd *qc);
+void (*bmdma_start) (struct ata_queued_cmd *qc);
+	</programlisting>
+
+	<para>
+	When setting up an IDE BMDMA transaction, these hooks arm
+	(->bmdma_setup) and fire (->bmdma_start) the hardware's DMA
+	engine.
+	</para>
+
+	<programlisting>
+void (*qc_prep) (struct ata_queued_cmd *qc);
+int (*qc_issue) (struct ata_queued_cmd *qc);
+	</programlisting>
+
+	<para>
+	Higher-level hooks, these two hooks can potentially supercede
+	several of the above taskfile/DMA engine hooks.  ->qc_prep is
+	called after the buffers have been DMA-mapped, and is typically
+	used to populate the hardware's DMA scatter-gather table.
+	Most drivers use the standard ata_qc_prep() helper function, but
+	more advanced drivers roll their own.
+	</para>
+	<para>
+	->qc_issue is used to make a command active, once the hardware
+	and S/G tables have been prepared.  IDE BMDMA drivers use the
+	helper function ata_qc_issue_prot() for taskfile protocol-based
+	dispatch.  More advanced drivers roll their own ->qc_issue
+	implementation, using this as the "issue new ATA command to
+	hardware" hook.
+	</para>
+
+	<programlisting>
+void (*eng_timeout) (struct ata_port *ap);
+	</programlisting>
+
+	<para>
+	This is a high level error handling function, called from the
+	error handling thread, when a command times out.
+	</para>
+
+	<programlisting>
+irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
+void (*irq_clear) (struct ata_port *);
+	</programlisting>
+
+	<para>
+	->irq_handler is the interrupt handling routine registered with
+	the system, by libata.  ->irq_clear is called during probe just
+	before the interrupt handler is registered, to be sure hardware
+	is quiet.
+	</para>
+
+	<programlisting>
+u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
+void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
+                   u32 val);
+	</programlisting>
+
+	<para>
+	Read and write standard SATA phy registers.  Currently only used
+	if ->phy_reset hook called the sata_phy_reset() helper function.
+	</para>
+
+	<programlisting>
+int (*port_start) (struct ata_port *ap);
+void (*port_stop) (struct ata_port *ap);
+void (*host_stop) (struct ata_host_set *host_set);
+	</programlisting>
+
+	<para>
+	->port_start() is called just after the data structures for each
+	port are initialized.  Typically this is used to alloc per-port
+	DMA buffers / tables / rings, enable DMA engines, and similar
+	tasks.  
+	</para>
+	<para>
+	->host_stop() is called when the rmmod or hot unplug process
+	begins.  The hook must stop all hardware interrupts, DMA
+	engines, etc.
+	</para>
+	<para>
+	->port_stop() is called after ->host_stop().  It's sole function
+	is to release DMA/memory resources, now that they are no longer
+	actively being used.
+	</para>
+
+     </sect1>
+  </chapter>
+
+  <chapter id="libataExt">
+     <title>libata Library</title>
+!Edrivers/scsi/libata-core.c
+  </chapter>
+
+  <chapter id="libataInt">
+     <title>libata Core Internals</title>
+!Idrivers/scsi/libata-core.c
+  </chapter>
+
+  <chapter id="libataScsiInt">
+     <title>libata SCSI translation/emulation</title>
+!Edrivers/scsi/libata-scsi.c
+!Idrivers/scsi/libata-scsi.c
+  </chapter>
+
+  <chapter id="PiixInt">
+     <title>ata_piix Internals</title>
+!Idrivers/scsi/ata_piix.c
+  </chapter>
+
+  <chapter id="SILInt">
+     <title>sata_sil Internals</title>
+!Idrivers/scsi/sata_sil.c
+  </chapter>
+
+</book>
diff --git a/Documentation/DocBook/librs.tmpl b/Documentation/DocBook/librs.tmpl
new file mode 100644
index 000000000000..3ff39bafc00e
--- /dev/null
+++ b/Documentation/DocBook/librs.tmpl
@@ -0,0 +1,289 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="Reed-Solomon-Library-Guide">
+ <bookinfo>
+  <title>Reed-Solomon Library Programming Interface</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Thomas</firstname>
+    <surname>Gleixner</surname>
+    <affiliation>
+     <address>
+      <email>tglx@linutronix.de</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2004</year>
+   <holder>Thomas Gleixner</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License version 2 as published by the Free Software Foundation.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="intro">
+      <title>Introduction</title>
+  <para>
+  	The generic Reed-Solomon Library provides encoding, decoding
+	and error correction functions.
+  </para>
+  <para>
+  	Reed-Solomon codes are used in communication and storage
+	applications to ensure data integrity. 
+  </para>
+  <para>
+  	This documentation is provided for developers who want to utilize
+	the functions provided by the library.
+  </para>
+  </chapter>
+  
+  <chapter id="bugs">
+     <title>Known Bugs And Assumptions</title>
+  <para>
+	None.	
+  </para>
+  </chapter>
+
+  <chapter id="usage">
+     	<title>Usage</title>
+	<para>
+		This chapter provides examples how to use the library.
+	</para>
+	<sect1>
+		<title>Initializing</title>
+		<para>
+			The init function init_rs returns a pointer to a
+			rs decoder structure, which holds the necessary
+			information for encoding, decoding and error correction
+			with the given polynomial. It either uses an existing
+			matching decoder or creates a new one. On creation all
+			the lookup tables for fast en/decoding are created.
+			The function may take a while, so make sure not to 
+			call it in critical code paths.
+		</para>
+		<programlisting>
+/* the Reed Solomon control structure */
+static struct rs_control *rs_decoder;
+
+/* Symbolsize is 10 (bits)
+ * Primitve polynomial is x^10+x^3+1
+ * first consecutive root is 0
+ * primitve element to generate roots = 1
+ * generator polinomial degree (number of roots) = 6
+ */
+rs_decoder = init_rs (10, 0x409, 0, 1, 6);
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Encoding</title>
+		<para>
+			The encoder calculates the Reed-Solomon code over
+			the given data length and stores the result in 
+			the parity buffer. Note that the parity buffer must
+			be initialized before calling the encoder.
+		</para>
+		<para>
+			The expanded data can be inverted on the fly by
+			providing a non zero inversion mask. The expanded data is
+			XOR'ed with the mask. This is used e.g. for FLASH
+			ECC, where the all 0xFF is inverted to an all 0x00.
+			The Reed-Solomon code for all 0x00 is all 0x00. The
+			code is inverted before storing to FLASH so it is 0xFF
+			too. This prevent's that reading from an erased FLASH
+			results in ECC errors.
+		</para>
+		<para>
+			The databytes are expanded to the given symbol size
+			on the fly. There is no support for encoding continuous
+			bitstreams with a symbol size != 8 at the moment. If
+			it is necessary it should be not a big deal to implement
+			such functionality.
+		</para>
+		<programlisting>
+/* Parity buffer. Size = number of roots */
+uint16_t par[6];
+/* Initialize the parity buffer */
+memset(par, 0, sizeof(par));
+/* Encode 512 byte in data8. Store parity in buffer par */
+encode_rs8 (rs_decoder, data8, 512, par, 0);
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Decoding</title>
+		<para>
+			The decoder calculates the syndrome over
+			the given data length and the received parity symbols
+			and corrects errors in the data.
+		</para>
+		<para>
+			If a syndrome is available from a hardware decoder
+			then the syndrome calculation is skipped.
+		</para>
+		<para>
+			The correction of the data buffer can be suppressed
+			by providing a correction pattern buffer and an error
+			location buffer to the decoder. The decoder stores the
+			calculated error location and the correction bitmask
+			in the given buffers. This is useful for hardware
+			decoders which use a weird bit ordering scheme.
+		</para>
+		<para>
+			The databytes are expanded to the given symbol size
+			on the fly. There is no support for decoding continuous
+			bitstreams with a symbolsize != 8 at the moment. If
+			it is necessary it should be not a big deal to implement
+			such functionality.
+		</para>
+		
+		<sect2>
+		<title>
+			Decoding with syndrome calculation, direct data correction
+		</title>
+		<programlisting>
+/* Parity buffer. Size = number of roots */
+uint16_t par[6];
+uint8_t  data[512];
+int numerr;
+/* Receive data */
+.....
+/* Receive parity */
+.....
+/* Decode 512 byte in data8.*/
+numerr = decode_rs8 (rs_decoder, data8, par, 512, NULL, 0, NULL, 0, NULL);
+		</programlisting>
+		</sect2>
+
+		<sect2>
+		<title>
+			Decoding with syndrome given by hardware decoder, direct data correction
+		</title>
+		<programlisting>
+/* Parity buffer. Size = number of roots */
+uint16_t par[6], syn[6];
+uint8_t  data[512];
+int numerr;
+/* Receive data */
+.....
+/* Receive parity */
+.....
+/* Get syndrome from hardware decoder */
+.....
+/* Decode 512 byte in data8.*/
+numerr = decode_rs8 (rs_decoder, data8, par, 512, syn, 0, NULL, 0, NULL);
+		</programlisting>
+		</sect2>
+
+		<sect2>
+		<title>
+			Decoding with syndrome given by hardware decoder, no direct data correction.
+		</title>
+		<para>
+			Note: It's not necessary to give data and received parity to the decoder.
+		</para>
+		<programlisting>
+/* Parity buffer. Size = number of roots */
+uint16_t par[6], syn[6], corr[8];
+uint8_t  data[512];
+int numerr, errpos[8];
+/* Receive data */
+.....
+/* Receive parity */
+.....
+/* Get syndrome from hardware decoder */
+.....
+/* Decode 512 byte in data8.*/
+numerr = decode_rs8 (rs_decoder, NULL, NULL, 512, syn, 0, errpos, 0, corr);
+for (i = 0; i &lt; numerr; i++) {
+	do_error_correction_in_your_buffer(errpos[i], corr[i]);
+}
+		</programlisting>
+		</sect2>
+	</sect1>
+	<sect1>
+		<title>Cleanup</title>
+		<para>
+			The function free_rs frees the allocated resources,
+			if the caller is the last user of the decoder.
+		</para>
+		<programlisting>
+/* Release resources */
+free_rs(rs_decoder);
+		</programlisting>
+	</sect1>
+
+  </chapter>
+	
+  <chapter id="structs">
+     <title>Structures</title>
+     <para>
+     This chapter contains the autogenerated documentation of the structures which are
+     used in the Reed-Solomon Library and are relevant for a developer.
+     </para>
+!Iinclude/linux/rslib.h
+  </chapter>
+
+  <chapter id="pubfunctions">
+     <title>Public Functions Provided</title>
+     <para>
+     This chapter contains the autogenerated documentation of the Reed-Solomon functions
+     which are exported.
+     </para>
+!Elib/reed_solomon/reed_solomon.c
+  </chapter>
+  
+  <chapter id="credits">
+     <title>Credits</title>
+	<para>
+		The library code for encoding and decoding was written by Phil Karn.
+	</para>
+	<programlisting>
+		Copyright 2002, Phil Karn, KA9Q
+ 		May be used under the terms of the GNU General Public License (GPL)
+	</programlisting>
+	<para>
+		The wrapper functions and interfaces are written by Thomas Gleixner
+	</para>
+	<para>
+		Many users have provided bugfixes, improvements and helping hands for testing.
+		Thanks a lot.
+	</para>
+	<para>
+		The following people have contributed to this document:
+	</para>
+	<para>
+		Thomas Gleixner<email>tglx@linutronix.de</email>
+	</para>
+  </chapter>
+</book>
diff --git a/Documentation/DocBook/lsm.tmpl b/Documentation/DocBook/lsm.tmpl
new file mode 100644
index 000000000000..f63822195871
--- /dev/null
+++ b/Documentation/DocBook/lsm.tmpl
@@ -0,0 +1,265 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<article class="whitepaper" id="LinuxSecurityModule" lang="en">
+ <articleinfo>
+ <title>Linux Security Modules:  General Security Hooks for Linux</title>
+ <authorgroup>
+ <author>
+ <firstname>Stephen</firstname> 
+ <surname>Smalley</surname>
+ <affiliation>
+ <orgname>NAI Labs</orgname>
+ <address><email>ssmalley@nai.com</email></address>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>Timothy</firstname> 
+ <surname>Fraser</surname>
+ <affiliation>
+ <orgname>NAI Labs</orgname>
+ <address><email>tfraser@nai.com</email></address>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>Chris</firstname> 
+ <surname>Vance</surname>
+ <affiliation>
+ <orgname>NAI Labs</orgname>
+ <address><email>cvance@nai.com</email></address>
+ </affiliation>
+ </author>
+ </authorgroup>
+ </articleinfo>
+
+<sect1><title>Introduction</title>
+
+<para>
+In March 2001, the National Security Agency (NSA) gave a presentation
+about Security-Enhanced Linux (SELinux) at the 2.5 Linux Kernel
+Summit.  SELinux is an implementation of flexible and fine-grained
+nondiscretionary access controls in the Linux kernel, originally
+implemented as its own particular kernel patch.  Several other
+security projects (e.g. RSBAC, Medusa) have also developed flexible
+access control architectures for the Linux kernel, and various
+projects have developed particular access control models for Linux
+(e.g. LIDS, DTE, SubDomain).  Each project has developed and
+maintained its own kernel patch to support its security needs.
+</para>
+
+<para>
+In response to the NSA presentation, Linus Torvalds made a set of
+remarks that described a security framework he would be willing to
+consider for inclusion in the mainstream Linux kernel.  He described a
+general framework that would provide a set of security hooks to
+control operations on kernel objects and a set of opaque security
+fields in kernel data structures for maintaining security attributes.
+This framework could then be used by loadable kernel modules to
+implement any desired model of security.  Linus also suggested the
+possibility of migrating the Linux capabilities code into such a
+module.
+</para>
+
+<para>
+The Linux Security Modules (LSM) project was started by WireX to
+develop such a framework.  LSM is a joint development effort by
+several security projects, including Immunix, SELinux, SGI and Janus,
+and several individuals, including Greg Kroah-Hartman and James
+Morris, to develop a Linux kernel patch that implements this
+framework.  The patch is currently tracking the 2.4 series and is
+targeted for integration into the 2.5 development series.  This
+technical report provides an overview of the framework and the example
+capabilities security module provided by the LSM kernel patch.
+</para>
+
+</sect1>
+
+<sect1 id="framework"><title>LSM Framework</title>
+
+<para>
+The LSM kernel patch provides a general kernel framework to support
+security modules.  In particular, the LSM framework is primarily
+focused on supporting access control modules, although future
+development is likely to address other security needs such as
+auditing.  By itself, the framework does not provide any additional
+security; it merely provides the infrastructure to support security
+modules.  The LSM kernel patch also moves most of the capabilities
+logic into an optional security module, with the system defaulting
+to the traditional superuser logic.  This capabilities module
+is discussed further in <xref linkend="cap"/>.
+</para>
+
+<para>
+The LSM kernel patch adds security fields to kernel data structures
+and inserts calls to hook functions at critical points in the kernel
+code to manage the security fields and to perform access control.  It
+also adds functions for registering and unregistering security
+modules, and adds a general <function>security</function> system call
+to support new system calls for security-aware applications.
+</para>
+
+<para>
+The LSM security fields are simply <type>void*</type> pointers.  For
+process and program execution security information, security fields
+were added to <structname>struct task_struct</structname> and 
+<structname>struct linux_binprm</structname>.  For filesystem security
+information, a security field was added to 
+<structname>struct super_block</structname>.  For pipe, file, and socket
+security information, security fields were added to 
+<structname>struct inode</structname> and 
+<structname>struct file</structname>.  For packet and network device security
+information, security fields were added to
+<structname>struct sk_buff</structname> and
+<structname>struct net_device</structname>.  For System V IPC security
+information, security fields were added to
+<structname>struct kern_ipc_perm</structname> and
+<structname>struct msg_msg</structname>; additionally, the definitions
+for <structname>struct msg_msg</structname>, <structname>struct 
+msg_queue</structname>, and <structname>struct 
+shmid_kernel</structname> were moved to header files
+(<filename>include/linux/msg.h</filename> and
+<filename>include/linux/shm.h</filename> as appropriate) to allow
+the security modules to use these definitions.
+</para>
+
+<para>
+Each LSM hook is a function pointer in a global table,
+security_ops. This table is a
+<structname>security_operations</structname> structure as defined by
+<filename>include/linux/security.h</filename>.  Detailed documentation
+for each hook is included in this header file.  At present, this
+structure consists of a collection of substructures that group related
+hooks based on the kernel object (e.g. task, inode, file, sk_buff,
+etc) as well as some top-level hook function pointers for system
+operations.  This structure is likely to be flattened in the future
+for performance.  The placement of the hook calls in the kernel code
+is described by the "called:" lines in the per-hook documentation in
+the header file.  The hook calls can also be easily found in the
+kernel code by looking for the string "security_ops->".
+
+</para>
+
+<para>
+Linus mentioned per-process security hooks in his original remarks as a
+possible alternative to global security hooks.  However, if LSM were
+to start from the perspective of per-process hooks, then the base
+framework would have to deal with how to handle operations that
+involve multiple processes (e.g. kill), since each process might have
+its own hook for controlling the operation.  This would require a
+general mechanism for composing hooks in the base framework.
+Additionally, LSM would still need global hooks for operations that
+have no process context (e.g. network input operations).
+Consequently, LSM provides global security hooks, but a security
+module is free to implement per-process hooks (where that makes sense)
+by storing a security_ops table in each process' security field and
+then invoking these per-process hooks from the global hooks.
+The problem of composition is thus deferred to the module.
+</para>
+
+<para>
+The global security_ops table is initialized to a set of hook
+functions provided by a dummy security module that provides
+traditional superuser logic.  A <function>register_security</function>
+function (in <filename>security/security.c</filename>) is provided to
+allow a security module to set security_ops to refer to its own hook
+functions, and an <function>unregister_security</function> function is
+provided to revert security_ops to the dummy module hooks.  This
+mechanism is used to set the primary security module, which is
+responsible for making the final decision for each hook.
+</para>
+
+<para>
+LSM also provides a simple mechanism for stacking additional security
+modules with the primary security module.  It defines
+<function>register_security</function> and
+<function>unregister_security</function> hooks in the
+<structname>security_operations</structname> structure and provides
+<function>mod_reg_security</function> and
+<function>mod_unreg_security</function> functions that invoke these
+hooks after performing some sanity checking.  A security module can
+call these functions in order to stack with other modules.  However,
+the actual details of how this stacking is handled are deferred to the
+module, which can implement these hooks in any way it wishes
+(including always returning an error if it does not wish to support
+stacking).  In this manner, LSM again defers the problem of
+composition to the module.
+</para>
+
+<para>
+Although the LSM hooks are organized into substructures based on
+kernel object, all of the hooks can be viewed as falling into two
+major categories: hooks that are used to manage the security fields
+and hooks that are used to perform access control.  Examples of the
+first category of hooks include the
+<function>alloc_security</function> and
+<function>free_security</function> hooks defined for each kernel data
+structure that has a security field.  These hooks are used to allocate
+and free security structures for kernel objects.  The first category
+of hooks also includes hooks that set information in the security
+field after allocation, such as the <function>post_lookup</function>
+hook in <structname>struct inode_security_ops</structname>.  This hook
+is used to set security information for inodes after successful lookup
+operations.  An example of the second category of hooks is the
+<function>permission</function> hook in 
+<structname>struct inode_security_ops</structname>.  This hook checks
+permission when accessing an inode.
+</para>
+
+</sect1>
+
+<sect1 id="cap"><title>LSM Capabilities Module</title>
+
+<para>
+The LSM kernel patch moves most of the existing POSIX.1e capabilities
+logic into an optional security module stored in the file
+<filename>security/capability.c</filename>.  This change allows
+users who do not want to use capabilities to omit this code entirely
+from their kernel, instead using the dummy module for traditional
+superuser logic or any other module that they desire.  This change
+also allows the developers of the capabilities logic to maintain and
+enhance their code more freely, without needing to integrate patches
+back into the base kernel.
+</para>
+
+<para>
+In addition to moving the capabilities logic, the LSM kernel patch
+could move the capability-related fields from the kernel data
+structures into the new security fields managed by the security
+modules.  However, at present, the LSM kernel patch leaves the
+capability fields in the kernel data structures.  In his original
+remarks, Linus suggested that this might be preferable so that other
+security modules can be easily stacked with the capabilities module
+without needing to chain multiple security structures on the security field.
+It also avoids imposing extra overhead on the capabilities module
+to manage the security fields.  However, the LSM framework could
+certainly support such a move if it is determined to be desirable,
+with only a few additional changes described below.
+</para>
+
+<para>
+At present, the capabilities logic for computing process capabilities
+on <function>execve</function> and <function>set*uid</function>,
+checking capabilities for a particular process, saving and checking
+capabilities for netlink messages, and handling the
+<function>capget</function> and <function>capset</function> system
+calls have been moved into the capabilities module.  There are still a
+few locations in the base kernel where capability-related fields are
+directly examined or modified, but the current version of the LSM
+patch does allow a security module to completely replace the
+assignment and testing of capabilities.  These few locations would
+need to be changed if the capability-related fields were moved into
+the security field.  The following is a list of known locations that
+still perform such direct examination or modification of
+capability-related fields:
+<itemizedlist>
+<listitem><para><filename>fs/open.c</filename>:<function>sys_access</function></para></listitem>
+<listitem><para><filename>fs/lockd/host.c</filename>:<function>nlm_bind_host</function></para></listitem>
+<listitem><para><filename>fs/nfsd/auth.c</filename>:<function>nfsd_setuser</function></para></listitem>
+<listitem><para><filename>fs/proc/array.c</filename>:<function>task_cap</function></para></listitem>
+</itemizedlist>
+</para>
+
+</sect1>
+
+</article>
diff --git a/Documentation/DocBook/man/Makefile b/Documentation/DocBook/man/Makefile
new file mode 100644
index 000000000000..4fb7ea0f7ac8
--- /dev/null
+++ b/Documentation/DocBook/man/Makefile
@@ -0,0 +1,3 @@
+# Rules are put in Documentation/DocBook
+
+clean-files := *.9.gz *.sgml manpage.links manpage.refs
diff --git a/Documentation/DocBook/mcabook.tmpl b/Documentation/DocBook/mcabook.tmpl
new file mode 100644
index 000000000000..4367f4642f3d
--- /dev/null
+++ b/Documentation/DocBook/mcabook.tmpl
@@ -0,0 +1,107 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="MCAGuide">
+ <bookinfo>
+  <title>MCA Driver Programming Interface</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Alan</firstname>
+    <surname>Cox</surname>
+    <affiliation>
+     <address>
+      <email>alan@redhat.com</email>
+     </address>
+    </affiliation>
+   </author>
+   <author>
+    <firstname>David</firstname>
+    <surname>Weinehall</surname>
+   </author>
+   <author>
+    <firstname>Chris</firstname>
+    <surname>Beauregard</surname>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2000</year>
+   <holder>Alan Cox</holder>
+   <holder>David Weinehall</holder>
+   <holder>Chris Beauregard</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="intro">
+      <title>Introduction</title>
+  <para>
+	The MCA bus functions provide a generalised interface to find MCA
+	bus cards, to claim them for a driver, and to read and manipulate POS 
+	registers without being aware of the motherboard internals or 
+	certain deep magic specific to onboard devices.
+  </para>
+  <para>
+	The basic interface to the MCA bus devices is the slot. Each slot
+	is numbered and virtual slot numbers are assigned to the internal
+	devices. Using a pci_dev as other busses do does not really make
+	sense in the MCA context as the MCA bus resources require card
+	specific interpretation.
+  </para>
+  <para>
+	Finally the MCA bus functions provide a parallel set of DMA
+	functions mimicing the ISA bus DMA functions as closely as possible,
+	although also supporting the additional DMA functionality on the
+	MCA bus controllers.
+  </para>
+  </chapter>
+  <chapter id="bugs">
+     <title>Known Bugs And Assumptions</title>
+  <para>
+	None.	
+  </para>
+  </chapter>
+
+  <chapter id="pubfunctions">
+     <title>Public Functions Provided</title>
+!Earch/i386/kernel/mca.c
+  </chapter>
+
+  <chapter id="dmafunctions">
+     <title>DMA Functions Provided</title>
+!Iinclude/asm-i386/mca_dma.h
+  </chapter>
+
+</book>
diff --git a/Documentation/DocBook/mtdnand.tmpl b/Documentation/DocBook/mtdnand.tmpl
new file mode 100644
index 000000000000..6e463d0db266
--- /dev/null
+++ b/Documentation/DocBook/mtdnand.tmpl
@@ -0,0 +1,1320 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="MTD-NAND-Guide">
+ <bookinfo>
+  <title>MTD NAND Driver Programming Interface</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Thomas</firstname>
+    <surname>Gleixner</surname>
+    <affiliation>
+     <address>
+      <email>tglx@linutronix.de</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2004</year>
+   <holder>Thomas Gleixner</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License version 2 as published by the Free Software Foundation.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="intro">
+      <title>Introduction</title>
+  <para>
+  	The generic NAND driver supports almost all NAND and AG-AND based
+	chips and connects them to the Memory Technology Devices (MTD)
+	subsystem of the Linux Kernel.
+  </para>
+  <para>
+  	This documentation is provided for developers who want to implement
+	board drivers or filesystem drivers suitable for NAND devices.
+  </para>
+  </chapter>
+  
+  <chapter id="bugs">
+     <title>Known Bugs And Assumptions</title>
+  <para>
+	None.	
+  </para>
+  </chapter>
+
+  <chapter id="dochints">
+     <title>Documentation hints</title>
+     <para>
+     The function and structure docs are autogenerated. Each function and 
+     struct member has a short description which is marked with an [XXX] identifier.
+     The following chapters explain the meaning of those identifiers.
+     </para>
+     <sect1>   
+	<title>Function identifiers [XXX]</title>
+     	<para>
+	The functions are marked with [XXX] identifiers in the short
+	comment. The identifiers explain the usage and scope of the
+	functions. Following identifiers are used:
+     	</para>
+	<itemizedlist>
+		<listitem><para>
+	  	[MTD Interface]</para><para>
+		These functions provide the interface to the MTD kernel API. 
+		They are not replacable and provide functionality
+		which is complete hardware independent.
+		</para></listitem>
+		<listitem><para>
+	  	[NAND Interface]</para><para>
+		These functions are exported and provide the interface to the NAND kernel API. 
+		</para></listitem>
+		<listitem><para>
+	  	[GENERIC]</para><para>
+		Generic functions are not replacable and provide functionality
+		which is complete hardware independent.
+		</para></listitem>
+		<listitem><para>
+	  	[DEFAULT]</para><para>
+		Default functions provide hardware related functionality which is suitable
+		for most of the implementations. These functions can be replaced by the
+		board driver if neccecary. Those functions are called via pointers in the
+		NAND chip description structure. The board driver can set the functions which
+		should be replaced by board dependend functions before calling nand_scan().
+		If the function pointer is NULL on entry to nand_scan() then the pointer
+		is set to the default function which is suitable for the detected chip type.
+		</para></listitem>
+	</itemizedlist>
+     </sect1>
+     <sect1>   
+	<title>Struct member identifiers [XXX]</title>
+     	<para>
+	The struct members are marked with [XXX] identifiers in the 
+	comment. The identifiers explain the usage and scope of the
+	members. Following identifiers are used:
+     	</para>
+	<itemizedlist>
+		<listitem><para>
+	  	[INTERN]</para><para>
+		These members are for NAND driver internal use only and must not be
+		modified. Most of these values are calculated from the chip geometry
+		information which is evaluated during nand_scan().
+		</para></listitem>
+		<listitem><para>
+	  	[REPLACEABLE]</para><para>
+		Replaceable members hold hardware related functions which can be 
+		provided by the board driver. The board driver can set the functions which
+		should be replaced by board dependend functions before calling nand_scan().
+		If the function pointer is NULL on entry to nand_scan() then the pointer
+		is set to the default function which is suitable for the detected chip type.
+		</para></listitem>
+		<listitem><para>
+	  	[BOARDSPECIFIC]</para><para>
+		Board specific members hold hardware related information which must
+		be provided by the board driver. The board driver must set the function
+		pointers and datafields before calling nand_scan().
+		</para></listitem>
+		<listitem><para>
+	  	[OPTIONAL]</para><para>
+		Optional members can hold information relevant for the board driver. The
+		generic NAND driver code does not use this information.
+		</para></listitem>
+	</itemizedlist>
+     </sect1>
+  </chapter>   
+
+  <chapter id="basicboarddriver">
+     	<title>Basic board driver</title>
+	<para>
+		For most boards it will be sufficient to provide just the
+		basic functions and fill out some really board dependend
+		members in the nand chip description structure.
+		See drivers/mtd/nand/skeleton for reference.
+	</para>
+	<sect1>
+		<title>Basic defines</title>
+		<para>
+			At least you have to provide a mtd structure and
+			a storage for the ioremap'ed chip address.
+			You can allocate the mtd structure using kmalloc
+			or you can allocate it statically.
+			In case of static allocation you have to allocate
+			a nand_chip structure too.
+		</para>
+		<para>
+			Kmalloc based example
+		</para>
+		<programlisting>
+static struct mtd_info *board_mtd;
+static unsigned long baseaddr;
+		</programlisting>
+		<para>
+			Static example
+		</para>
+		<programlisting>
+static struct mtd_info board_mtd;
+static struct nand_chip board_chip;
+static unsigned long baseaddr;
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Partition defines</title>
+		<para>
+			If you want to divide your device into parititions, then
+			enable the configuration switch CONFIG_MTD_PARITIONS and define
+			a paritioning scheme suitable to your board.
+		</para>
+		<programlisting>
+#define NUM_PARTITIONS 2
+static struct mtd_partition partition_info[] = {
+	{ .name = "Flash partition 1",
+	  .offset =  0,
+	  .size =    8 * 1024 * 1024 },
+	{ .name = "Flash partition 2",
+	  .offset =  MTDPART_OFS_NEXT,
+	  .size =    MTDPART_SIZ_FULL },
+};
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Hardware control function</title>
+		<para>
+			The hardware control function provides access to the 
+			control pins of the NAND chip(s). 
+			The access can be done by GPIO pins or by address lines.
+			If you use address lines, make sure that the timing
+			requirements are met.
+		</para>
+		<para>
+			<emphasis>GPIO based example</emphasis>
+		</para>
+		<programlisting>
+static void board_hwcontrol(struct mtd_info *mtd, int cmd)
+{
+	switch(cmd){
+		case NAND_CTL_SETCLE: /* Set CLE pin high */ break;
+		case NAND_CTL_CLRCLE: /* Set CLE pin low */ break;
+		case NAND_CTL_SETALE: /* Set ALE pin high */ break;
+		case NAND_CTL_CLRALE: /* Set ALE pin low */ break;
+		case NAND_CTL_SETNCE: /* Set nCE pin low */ break;
+		case NAND_CTL_CLRNCE: /* Set nCE pin high */ break;
+	}
+}
+		</programlisting>
+		<para>
+			<emphasis>Address lines based example.</emphasis> It's assumed that the
+			nCE pin is driven by a chip select decoder.
+		</para>
+		<programlisting>
+static void board_hwcontrol(struct mtd_info *mtd, int cmd)
+{
+	struct nand_chip *this = (struct nand_chip *) mtd->priv;
+	switch(cmd){
+		case NAND_CTL_SETCLE: this->IO_ADDR_W |= CLE_ADRR_BIT;  break;
+		case NAND_CTL_CLRCLE: this->IO_ADDR_W &amp;= ~CLE_ADRR_BIT; break;
+		case NAND_CTL_SETALE: this->IO_ADDR_W |= ALE_ADRR_BIT;  break;
+		case NAND_CTL_CLRALE: this->IO_ADDR_W &amp;= ~ALE_ADRR_BIT; break;
+	}
+}
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Device ready function</title>
+		<para>
+			If the hardware interface has the ready busy pin of the NAND chip connected to a
+			GPIO or other accesible I/O pin, this function is used to read back the state of the
+			pin. The function has no arguments and should return 0, if the device is busy (R/B pin 
+			is low) and 1, if the device is ready (R/B pin is high).
+			If the hardware interface does not give access to the ready busy pin, then
+			the function must not be defined and the function pointer this->dev_ready is set to NULL.		
+		</para>
+	</sect1>
+	<sect1>
+		<title>Init function</title>
+		<para>
+			The init function allocates memory and sets up all the board
+			specific parameters and function pointers. When everything
+			is set up nand_scan() is called. This function tries to
+			detect and identify then chip. If a chip is found all the
+			internal data fields are initialized accordingly.
+			The structure(s) have to be zeroed out first and then filled with the neccecary 
+			information about the device.
+		</para>
+		<programlisting>
+int __init board_init (void)
+{
+	struct nand_chip *this;
+	int err = 0;
+
+	/* Allocate memory for MTD device structure and private data */
+	board_mtd = kmalloc (sizeof(struct mtd_info) + sizeof (struct nand_chip), GFP_KERNEL);
+	if (!board_mtd) {
+		printk ("Unable to allocate NAND MTD device structure.\n");
+		err = -ENOMEM;
+		goto out;
+	}
+
+	/* Initialize structures */
+	memset ((char *) board_mtd, 0, sizeof(struct mtd_info) + sizeof(struct nand_chip));
+
+	/* map physical adress */
+	baseaddr = (unsigned long)ioremap(CHIP_PHYSICAL_ADDRESS, 1024);
+	if(!baseaddr){
+		printk("Ioremap to access NAND chip failed\n");
+		err = -EIO;
+		goto out_mtd;
+	}
+
+	/* Get pointer to private data */
+	this = (struct nand_chip *) ();
+	/* Link the private data with the MTD structure */
+	board_mtd->priv = this;
+
+	/* Set address of NAND IO lines */
+	this->IO_ADDR_R = baseaddr;
+	this->IO_ADDR_W = baseaddr;
+	/* Reference hardware control function */
+	this->hwcontrol = board_hwcontrol;
+	/* Set command delay time, see datasheet for correct value */
+	this->chip_delay = CHIP_DEPENDEND_COMMAND_DELAY;
+	/* Assign the device ready function, if available */
+	this->dev_ready = board_dev_ready;
+	this->eccmode = NAND_ECC_SOFT;
+
+	/* Scan to find existance of the device */
+	if (nand_scan (board_mtd, 1)) {
+		err = -ENXIO;
+		goto out_ior;
+	}
+	
+	add_mtd_partitions(board_mtd, partition_info, NUM_PARTITIONS);
+	goto out;
+
+out_ior:
+	iounmap((void *)baseaddr);
+out_mtd:
+	kfree (board_mtd);
+out:
+	return err;
+}
+module_init(board_init);
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Exit function</title>
+		<para>
+			The exit function is only neccecary if the driver is
+			compiled as a module. It releases all resources which
+			are held by the chip driver and unregisters the partitions
+			in the MTD layer.
+		</para>
+		<programlisting>
+#ifdef MODULE
+static void __exit board_cleanup (void)
+{
+	/* Release resources, unregister device */
+	nand_release (board_mtd);
+
+	/* unmap physical adress */
+	iounmap((void *)baseaddr);
+	
+	/* Free the MTD device structure */
+	kfree (board_mtd);
+}
+module_exit(board_cleanup);
+#endif
+		</programlisting>
+	</sect1>
+  </chapter>
+
+  <chapter id="boarddriversadvanced">
+     	<title>Advanced board driver functions</title>
+	<para>
+		This chapter describes the advanced functionality of the NAND
+		driver. For a list of functions which can be overridden by the board
+		driver see the documentation of the nand_chip structure.
+	</para>
+	<sect1>
+		<title>Multiple chip control</title>
+		<para>
+			The nand driver can control chip arrays. Therefor the
+			board driver must provide an own select_chip function. This
+			function must (de)select the requested chip.
+			The function pointer in the nand_chip structure must
+			be set before calling nand_scan(). The maxchip parameter
+			of nand_scan() defines the maximum number of chips to
+			scan for. Make sure that the select_chip function can
+			handle the requested number of chips.
+		</para>
+		<para>
+			The nand driver concatenates the chips to one virtual
+			chip and provides this virtual chip to the MTD layer.
+		</para>
+		<para>
+			<emphasis>Note: The driver can only handle linear chip arrays
+			of equally sized chips. There is no support for
+			parallel arrays which extend the buswidth.</emphasis>
+		</para>
+		<para>
+			<emphasis>GPIO based example</emphasis>
+		</para>
+		<programlisting>
+static void board_select_chip (struct mtd_info *mtd, int chip)
+{
+	/* Deselect all chips, set all nCE pins high */
+	GPIO(BOARD_NAND_NCE) |= 0xff;	
+	if (chip >= 0)
+		GPIO(BOARD_NAND_NCE) &amp;= ~ (1 &lt;&lt; chip);
+}
+		</programlisting>
+		<para>
+			<emphasis>Address lines based example.</emphasis>
+			Its assumed that the nCE pins are connected to an
+			address decoder.
+		</para>
+		<programlisting>
+static void board_select_chip (struct mtd_info *mtd, int chip)
+{
+	struct nand_chip *this = (struct nand_chip *) mtd->priv;
+	
+	/* Deselect all chips */
+	this->IO_ADDR_R &amp;= ~BOARD_NAND_ADDR_MASK;
+	this->IO_ADDR_W &amp;= ~BOARD_NAND_ADDR_MASK;
+	switch (chip) {
+	case 0:
+		this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIP0;
+		this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIP0;
+		break;
+	....	
+	case n:
+		this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIPn;
+		this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIPn;
+		break;
+	}	
+}
+		</programlisting>
+	</sect1>
+	<sect1>
+		<title>Hardware ECC support</title>
+		<sect2>
+			<title>Functions and constants</title>
+			<para>
+				The nand driver supports three different types of
+				hardware ECC.
+				<itemizedlist>
+				<listitem><para>NAND_ECC_HW3_256</para><para>
+				Hardware ECC generator providing 3 bytes ECC per
+				256 byte.
+				</para>	</listitem>
+				<listitem><para>NAND_ECC_HW3_512</para><para>
+				Hardware ECC generator providing 3 bytes ECC per
+				512 byte.
+				</para>	</listitem>
+				<listitem><para>NAND_ECC_HW6_512</para><para>
+				Hardware ECC generator providing 6 bytes ECC per
+				512 byte.
+				</para>	</listitem>
+				<listitem><para>NAND_ECC_HW8_512</para><para>
+				Hardware ECC generator providing 6 bytes ECC per
+				512 byte.
+				</para>	</listitem>
+				</itemizedlist>
+				If your hardware generator has a different functionality
+				add it at the appropriate place in nand_base.c
+			</para>
+			<para>
+				The board driver must provide following functions:
+				<itemizedlist>
+				<listitem><para>enable_hwecc</para><para>
+				This function is called before reading / writing to
+				the chip. Reset or initialize the hardware generator
+				in this function. The function is called with an
+				argument which let you distinguish between read 
+				and write operations.
+				</para>	</listitem>
+				<listitem><para>calculate_ecc</para><para>
+				This function is called after read / write from / to
+				the chip. Transfer the ECC from the hardware to
+				the buffer. If the option NAND_HWECC_SYNDROME is set
+				then the function is only called on write. See below.
+				</para>	</listitem>
+				<listitem><para>correct_data</para><para>
+				In case of an ECC error this function is called for
+				error detection and correction. Return 1 respectively 2
+				in case the error can be corrected. If the error is
+				not correctable return -1. If your hardware generator
+				matches the default algorithm of the nand_ecc software
+				generator then use the correction function provided
+				by nand_ecc instead of implementing duplicated code.
+				</para>	</listitem>
+				</itemizedlist>
+			</para>
+		</sect2>
+		<sect2>
+		<title>Hardware ECC with syndrome calculation</title>
+			<para>
+				Many hardware ECC implementations provide Reed-Solomon
+				codes and calculate an error syndrome on read. The syndrome
+				must be converted to a standard Reed-Solomon syndrome
+				before calling the error correction code in the generic
+				Reed-Solomon library.
+			</para>
+			<para>
+				The ECC bytes must be placed immidiately after the data
+				bytes in order to make the syndrome generator work. This
+				is contrary to the usual layout used by software ECC. The
+				seperation of data and out of band area is not longer
+				possible. The nand driver code handles this layout and
+				the remaining free bytes in the oob area are managed by 
+				the autoplacement code. Provide a matching oob-layout
+				in this case. See rts_from4.c and diskonchip.c for 
+				implementation reference. In those cases we must also
+				use bad block tables on FLASH, because the ECC layout is
+				interferring with the bad block marker positions.
+				See bad block table support for details.
+			</para>
+		</sect2>
+	</sect1>
+	<sect1>
+		<title>Bad block table support</title>
+		<para>
+			Most NAND chips mark the bad blocks at a defined
+			position in the spare area. Those blocks must 
+			not be erased under any circumstances as the bad 
+			block information would be lost.
+			It is possible to check the bad block mark each
+			time when the blocks are accessed by reading the
+			spare area of the first page in the block. This
+			is time consuming so a bad block table is used.
+		</para>
+		<para>
+			The nand driver supports various types of bad block
+			tables.
+			<itemizedlist>
+			<listitem><para>Per device</para><para>
+			The bad block table contains all bad block information
+			of the device which can consist of multiple chips.
+			</para>	</listitem>
+			<listitem><para>Per chip</para><para>
+			A bad block table is used per chip and contains the
+			bad block information for this particular chip.
+			</para>	</listitem>
+			<listitem><para>Fixed offset</para><para>
+			The bad block table is located at a fixed offset
+			in the chip (device). This applies to various
+			DiskOnChip devices.
+			</para>	</listitem>
+			<listitem><para>Automatic placed</para><para>
+			The bad block table is automatically placed and
+			detected either at the end or at the beginning
+			of a chip (device)
+			</para>	</listitem>
+			<listitem><para>Mirrored tables</para><para>
+			The bad block table is mirrored on the chip (device) to
+			allow updates of the bad block table without data loss.
+			</para>	</listitem>
+			</itemizedlist>
+		</para>
+		<para>	
+			nand_scan() calls the function nand_default_bbt(). 
+			nand_default_bbt() selects appropriate default
+			bad block table desriptors depending on the chip information
+			which was retrieved by nand_scan().
+		</para>
+		<para>
+			The standard policy is scanning the device for bad 
+			blocks and build a ram based bad block table which
+			allows faster access than always checking the
+			bad block information on the flash chip itself.
+		</para>
+		<sect2>
+			<title>Flash based tables</title>
+			<para>
+				It may be desired or neccecary to keep a bad block table in FLASH. 
+				For AG-AND chips this is mandatory, as they have no factory marked
+				bad blocks. They have factory marked good blocks. The marker pattern
+				is erased when the block is erased to be reused. So in case of
+				powerloss before writing the pattern back to the chip this block 
+				would be lost and added to the bad blocks. Therefor we scan the 
+				chip(s) when we detect them the first time for good blocks and 
+				store this information in a bad block table before erasing any 
+				of the blocks.
+			</para>
+			<para>
+				The blocks in which the tables are stored are procteted against
+				accidental access by marking them bad in the memory bad block
+				table. The bad block table managment functions are allowed
+				to circumvernt this protection.
+			</para>
+			<para>
+				The simplest way to activate the FLASH based bad block table support 
+				is to set the option NAND_USE_FLASH_BBT in the option field of
+				the nand chip structure before calling nand_scan(). For AG-AND
+				chips is this done by default.
+				This activates the default FLASH based bad block table functionality 
+				of the NAND driver. The default bad block table options are
+				<itemizedlist>
+				<listitem><para>Store bad block table per chip</para></listitem>
+				<listitem><para>Use 2 bits per block</para></listitem>
+				<listitem><para>Automatic placement at the end of the chip</para></listitem>
+				<listitem><para>Use mirrored tables with version numbers</para></listitem>
+				<listitem><para>Reserve 4 blocks at the end of the chip</para></listitem>
+				</itemizedlist>
+			</para>
+		</sect2>
+		<sect2>
+			<title>User defined tables</title>
+			<para>
+				User defined tables are created by filling out a 
+				nand_bbt_descr structure and storing the pointer in the
+				nand_chip structure member bbt_td before calling nand_scan(). 
+				If a mirror table is neccecary a second structure must be
+				created and a pointer to this structure must be stored
+				in bbt_md inside the nand_chip structure. If the bbt_md 
+				member is set to NULL then only the main table is used
+				and no scan for the mirrored table is performed.
+			</para>
+			<para>
+				The most important field in the nand_bbt_descr structure
+				is the options field. The options define most of the 
+				table properties. Use the predefined constants from
+				nand.h to define the options.
+				<itemizedlist>
+				<listitem><para>Number of bits per block</para>
+				<para>The supported number of bits is 1, 2, 4, 8.</para></listitem>
+				<listitem><para>Table per chip</para>
+				<para>Setting the constant NAND_BBT_PERCHIP selects that
+				a bad block table is managed for each chip in a chip array.
+				If this option is not set then a per device bad block table
+				is used.</para></listitem>
+				<listitem><para>Table location is absolute</para>
+				<para>Use the option constant NAND_BBT_ABSPAGE and
+				define the absolute page number where the bad block
+				table starts in the field pages. If you have selected bad block
+				tables per chip and you have a multi chip array then the start page
+				must be given for each chip in the chip array. Note: there is no scan
+				for a table ident pattern performed, so the fields 
+				pattern, veroffs, offs, len can be left uninitialized</para></listitem>
+				<listitem><para>Table location is automatically detected</para>
+				<para>The table can either be located in the first or the last good
+				blocks of the chip (device). Set NAND_BBT_LASTBLOCK to place
+				the bad block table at the end of the chip (device). The
+				bad block tables are marked and identified by a pattern which
+				is stored in the spare area of the first page in the block which
+				holds the bad block table. Store a pointer to the pattern  
+				in the pattern field. Further the length of the pattern has to be 
+				stored in len and the offset in the spare area must be given
+				in the offs member of the nand_bbt_descr stucture. For mirrored
+				bad block tables different patterns are mandatory.</para></listitem>
+				<listitem><para>Table creation</para>
+				<para>Set the option NAND_BBT_CREATE to enable the table creation
+				if no table can be found during the scan. Usually this is done only 
+				once if a new chip is found. </para></listitem>
+				<listitem><para>Table write support</para>
+				<para>Set the option NAND_BBT_WRITE to enable the table write support.
+				This allows the update of the bad block table(s) in case a block has
+				to be marked bad due to wear. The MTD interface function block_markbad
+				is calling the update function of the bad block table. If the write
+				support is enabled then the table is updated on FLASH.</para>
+				<para>
+				Note: Write support should only be enabled for mirrored tables with
+				version control.
+				</para></listitem>
+				<listitem><para>Table version control</para>
+				<para>Set the option NAND_BBT_VERSION to enable the table version control.
+				It's highly recommended to enable this for mirrored tables with write
+				support. It makes sure that the risk of loosing the bad block
+				table information is reduced to the loss of the information about the
+				one worn out block which should be marked bad. The version is stored in
+				4 consecutive bytes in the spare area of the device. The position of
+				the version number is defined by the member veroffs in the bad block table
+				descriptor.</para></listitem>
+				<listitem><para>Save block contents on write</para>
+				<para>
+				In case that the block which holds the bad block table does contain
+				other useful information, set the option NAND_BBT_SAVECONTENT. When
+				the bad block table is written then the whole block is read the bad
+				block table is updated and the block is erased and everything is 
+				written back. If this option is not set only the bad block table
+				is written and everything else in the block is ignored and erased.
+				</para></listitem>
+				<listitem><para>Number of reserved blocks</para>
+				<para>
+				For automatic placement some blocks must be reserved for
+				bad block table storage. The number of reserved blocks is defined 
+				in the maxblocks member of the babd block table description structure.
+				Reserving 4 blocks for mirrored tables should be a reasonable number. 
+				This also limits the number of blocks which are scanned for the bad
+				block table ident pattern.
+				</para></listitem>
+				</itemizedlist>
+			</para>
+		</sect2>
+	</sect1>
+	<sect1>
+		<title>Spare area (auto)placement</title>
+		<para>
+			The nand driver implements different possibilities for
+			placement of filesystem data in the spare area, 
+			<itemizedlist>
+			<listitem><para>Placement defined by fs driver</para></listitem>
+			<listitem><para>Automatic placement</para></listitem>
+			</itemizedlist>
+			The default placement function is automatic placement. The
+			nand driver has built in default placement schemes for the
+			various chiptypes. If due to hardware ECC functionality the
+			default placement does not fit then the board driver can
+			provide a own placement scheme.
+		</para>
+		<para>
+			File system drivers can provide a own placement scheme which
+			is used instead of the default placement scheme.
+		</para>
+		<para>
+			Placement schemes are defined by a nand_oobinfo structure
+	     		<programlisting>
+struct nand_oobinfo {
+	int	useecc;
+	int	eccbytes;
+	int	eccpos[24];
+	int	oobfree[8][2];
+};
+	     		</programlisting>
+			<itemizedlist>
+			<listitem><para>useecc</para><para>
+				The useecc member controls the ecc and placement function. The header
+				file include/mtd/mtd-abi.h contains constants to select ecc and
+				placement. MTD_NANDECC_OFF switches off the ecc complete. This is
+				not recommended and available for testing and diagnosis only.
+				MTD_NANDECC_PLACE selects caller defined placement, MTD_NANDECC_AUTOPLACE
+				selects automatic placement.
+			</para></listitem>
+			<listitem><para>eccbytes</para><para>
+				The eccbytes member defines the number of ecc bytes per page.
+			</para></listitem>
+			<listitem><para>eccpos</para><para>
+				The eccpos array holds the byte offsets in the spare area where
+				the ecc codes are placed.
+			</para></listitem>
+			<listitem><para>oobfree</para><para>
+				The oobfree array defines the areas in the spare area which can be
+				used for automatic placement. The information is given in the format
+				{offset, size}. offset defines the start of the usable area, size the
+				length in bytes. More than one area can be defined. The list is terminated
+				by an {0, 0} entry.
+			</para></listitem>
+			</itemizedlist>
+		</para>
+		<sect2>
+			<title>Placement defined by fs driver</title>
+			<para>
+				The calling function provides a pointer to a nand_oobinfo
+				structure which defines the ecc placement. For writes the
+				caller must provide a spare area buffer along with the
+				data buffer. The spare area buffer size is (number of pages) *
+				(size of spare area). For reads the buffer size is
+				(number of pages) * ((size of spare area) + (number of ecc
+				steps per page) * sizeof (int)). The driver stores the
+				result of the ecc check for each tuple in the spare buffer.
+				The storage sequence is 
+			</para>
+			<para>
+				&lt;spare data page 0&gt;&lt;ecc result 0&gt;...&lt;ecc result n&gt;
+			</para>
+			<para>
+				...
+			</para>
+			<para>
+				&lt;spare data page n&gt;&lt;ecc result 0&gt;...&lt;ecc result n&gt;
+			</para>
+			<para>
+				This is a legacy mode used by YAFFS1.
+			</para>
+			<para>
+				If the spare area buffer is NULL then only the ECC placement is
+				done according to the given scheme in the nand_oobinfo structure.
+			</para>
+		</sect2>
+		<sect2>
+			<title>Automatic placement</title>
+			<para>
+				Automatic placement uses the built in defaults to place the
+				ecc bytes in the spare area. If filesystem data have to be stored /
+				read into the spare area then the calling function must provide a
+				buffer. The buffer size per page is determined by the oobfree array in
+				the nand_oobinfo structure.
+			</para>
+			<para>
+				If the spare area buffer is NULL then only the ECC placement is
+				done according to the default builtin scheme.
+			</para>
+		</sect2>
+		<sect2>
+			<title>User space placement selection</title>
+		<para>
+			All non ecc functions like mtd->read and mtd->write use an internal 
+			structure, which can be set by an ioctl. This structure is preset 
+			to the autoplacement default.
+	     		<programlisting>
+	ioctl (fd, MEMSETOOBSEL, oobsel);
+	     		</programlisting>
+			oobsel is a pointer to a user supplied structure of type
+			nand_oobconfig. The contents of this structure must match the 
+			criteria of the filesystem, which will be used. See an example in utils/nandwrite.c.
+		</para>
+		</sect2>
+	</sect1>	
+	<sect1>
+		<title>Spare area autoplacement default schemes</title>
+		<sect2>
+			<title>256 byte pagesize</title>
+<informaltable><tgroup cols="3"><tbody>
+<row>
+<entry>Offset</entry>
+<entry>Content</entry>
+<entry>Comment</entry>
+</row>
+<row>
+<entry>0x00</entry>
+<entry>ECC byte 0</entry>
+<entry>Error correction code byte 0</entry>
+</row>
+<row>
+<entry>0x01</entry>
+<entry>ECC byte 1</entry>
+<entry>Error correction code byte 1</entry>
+</row>
+<row>
+<entry>0x02</entry>
+<entry>ECC byte 2</entry>
+<entry>Error correction code byte 2</entry>
+</row>
+<row>
+<entry>0x03</entry>
+<entry>Autoplace 0</entry>
+<entry></entry>
+</row>
+<row>
+<entry>0x04</entry>
+<entry>Autoplace 1</entry>
+<entry></entry>
+</row>
+<row>
+<entry>0x05</entry>
+<entry>Bad block marker</entry>
+<entry>If any bit in this byte is zero, then this block is bad.
+This applies only to the first page in a block. In the remaining
+pages this byte is reserved</entry>
+</row>
+<row>
+<entry>0x06</entry>
+<entry>Autoplace 2</entry>
+<entry></entry>
+</row>
+<row>
+<entry>0x07</entry>
+<entry>Autoplace 3</entry>
+<entry></entry>
+</row>
+</tbody></tgroup></informaltable>
+		</sect2>
+		<sect2>
+			<title>512 byte pagesize</title>
+<informaltable><tgroup cols="3"><tbody>
+<row>
+<entry>Offset</entry>
+<entry>Content</entry>
+<entry>Comment</entry>
+</row>
+<row>
+<entry>0x00</entry>
+<entry>ECC byte 0</entry>
+<entry>Error correction code byte 0 of the lower 256 Byte data in
+this page</entry>
+</row>
+<row>
+<entry>0x01</entry>
+<entry>ECC byte 1</entry>
+<entry>Error correction code byte 1 of the lower 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x02</entry>
+<entry>ECC byte 2</entry>
+<entry>Error correction code byte 2 of the lower 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x03</entry>
+<entry>ECC byte 3</entry>
+<entry>Error correction code byte 0 of the upper 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x04</entry>
+<entry>reserved</entry>
+<entry>reserved</entry>
+</row>
+<row>
+<entry>0x05</entry>
+<entry>Bad block marker</entry>
+<entry>If any bit in this byte is zero, then this block is bad.
+This applies only to the first page in a block. In the remaining
+pages this byte is reserved</entry>
+</row>
+<row>
+<entry>0x06</entry>
+<entry>ECC byte 4</entry>
+<entry>Error correction code byte 1 of the upper 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x07</entry>
+<entry>ECC byte 5</entry>
+<entry>Error correction code byte 2 of the upper 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x08 - 0x0F</entry>
+<entry>Autoplace 0 - 7</entry>
+<entry></entry>
+</row>
+</tbody></tgroup></informaltable>
+		</sect2>
+		<sect2>
+			<title>2048 byte pagesize</title>
+<informaltable><tgroup cols="3"><tbody>
+<row>
+<entry>Offset</entry>
+<entry>Content</entry>
+<entry>Comment</entry>
+</row>
+<row>
+<entry>0x00</entry>
+<entry>Bad block marker</entry>
+<entry>If any bit in this byte is zero, then this block is bad.
+This applies only to the first page in a block. In the remaining
+pages this byte is reserved</entry>
+</row>
+<row>
+<entry>0x01</entry>
+<entry>Reserved</entry>
+<entry>Reserved</entry>
+</row>
+<row>
+<entry>0x02-0x27</entry>
+<entry>Autoplace 0 - 37</entry>
+<entry></entry>
+</row>
+<row>
+<entry>0x28</entry>
+<entry>ECC byte 0</entry>
+<entry>Error correction code byte 0 of the first 256 Byte data in
+this page</entry>
+</row>
+<row>
+<entry>0x29</entry>
+<entry>ECC byte 1</entry>
+<entry>Error correction code byte 1 of the first 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x2A</entry>
+<entry>ECC byte 2</entry>
+<entry>Error correction code byte 2 of the first 256 Bytes data in
+this page</entry>
+</row>
+<row>
+<entry>0x2B</entry>
+<entry>ECC byte 3</entry>
+<entry>Error correction code byte 0 of the second 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x2C</entry>
+<entry>ECC byte 4</entry>
+<entry>Error correction code byte 1 of the second 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x2D</entry>
+<entry>ECC byte 5</entry>
+<entry>Error correction code byte 2 of the second 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x2E</entry>
+<entry>ECC byte 6</entry>
+<entry>Error correction code byte 0 of the third 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x2F</entry>
+<entry>ECC byte 7</entry>
+<entry>Error correction code byte 1 of the third 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x30</entry>
+<entry>ECC byte 8</entry>
+<entry>Error correction code byte 2 of the third 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x31</entry>
+<entry>ECC byte 9</entry>
+<entry>Error correction code byte 0 of the fourth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x32</entry>
+<entry>ECC byte 10</entry>
+<entry>Error correction code byte 1 of the fourth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x33</entry>
+<entry>ECC byte 11</entry>
+<entry>Error correction code byte 2 of the fourth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x34</entry>
+<entry>ECC byte 12</entry>
+<entry>Error correction code byte 0 of the fifth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x35</entry>
+<entry>ECC byte 13</entry>
+<entry>Error correction code byte 1 of the fifth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x36</entry>
+<entry>ECC byte 14</entry>
+<entry>Error correction code byte 2 of the fifth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x37</entry>
+<entry>ECC byte 15</entry>
+<entry>Error correction code byte 0 of the sixt 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x38</entry>
+<entry>ECC byte 16</entry>
+<entry>Error correction code byte 1 of the sixt 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x39</entry>
+<entry>ECC byte 17</entry>
+<entry>Error correction code byte 2 of the sixt 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x3A</entry>
+<entry>ECC byte 18</entry>
+<entry>Error correction code byte 0 of the seventh 256 Bytes of
+data in this page</entry>
+</row>
+<row>
+<entry>0x3B</entry>
+<entry>ECC byte 19</entry>
+<entry>Error correction code byte 1 of the seventh 256 Bytes of
+data in this page</entry>
+</row>
+<row>
+<entry>0x3C</entry>
+<entry>ECC byte 20</entry>
+<entry>Error correction code byte 2 of the seventh 256 Bytes of
+data in this page</entry>
+</row>
+<row>
+<entry>0x3D</entry>
+<entry>ECC byte 21</entry>
+<entry>Error correction code byte 0 of the eigth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x3E</entry>
+<entry>ECC byte 22</entry>
+<entry>Error correction code byte 1 of the eigth 256 Bytes of data
+in this page</entry>
+</row>
+<row>
+<entry>0x3F</entry>
+<entry>ECC byte 23</entry>
+<entry>Error correction code byte 2 of the eigth 256 Bytes of data
+in this page</entry>
+</row>
+</tbody></tgroup></informaltable>
+		</sect2>
+     	</sect1>
+  </chapter>
+
+  <chapter id="filesystems">
+     	<title>Filesystem support</title>
+	<para>
+		The NAND driver provides all neccecary functions for a
+		filesystem via the MTD interface.
+	</para>
+	<para>
+		Filesystems must be aware of the NAND pecularities and
+		restrictions. One major restrictions of NAND Flash is, that you cannot 
+		write as often as you want to a page. The consecutive writes to a page, 
+		before erasing it again, are restricted to 1-3 writes, depending on the 
+		manufacturers specifications. This applies similar to the spare area. 
+	</para>
+	<para>
+		Therefor NAND aware filesystems must either write in page size chunks
+		or hold a writebuffer to collect smaller writes until they sum up to 
+		pagesize. Available NAND aware filesystems: JFFS2, YAFFS. 		
+	</para>
+	<para>
+		The spare area usage to store filesystem data is controlled by
+		the spare area placement functionality which is described in one
+		of the earlier chapters.
+	</para>
+  </chapter>	
+  <chapter id="tools">
+     	<title>Tools</title>
+	<para>
+		The MTD project provides a couple of helpful tools to handle NAND Flash.
+		<itemizedlist>
+		<listitem><para>flasherase, flasheraseall: Erase and format FLASH partitions</para></listitem>
+		<listitem><para>nandwrite: write filesystem images to NAND FLASH</para></listitem>
+		<listitem><para>nanddump: dump the contents of a NAND FLASH partitions</para></listitem>
+		</itemizedlist>
+	</para>
+	<para>
+		These tools are aware of the NAND restrictions. Please use those tools
+		instead of complaining about errors which are caused by non NAND aware
+		access methods.
+	</para>
+  </chapter>	
+
+  <chapter id="defines">
+     <title>Constants</title>
+     <para>
+     This chapter describes the constants which might be relevant for a driver developer.
+     </para>
+     <sect1>   
+	<title>Chip option constants</title>
+     	<sect2>   
+		<title>Constants for chip id table</title>
+     		<para>
+		These constants are defined in nand.h. They are ored together to describe
+		the chip functionality.
+     		<programlisting>
+/* Chip can not auto increment pages */
+#define NAND_NO_AUTOINCR	0x00000001
+/* Buswitdh is 16 bit */
+#define NAND_BUSWIDTH_16	0x00000002
+/* Device supports partial programming without padding */
+#define NAND_NO_PADDING		0x00000004
+/* Chip has cache program function */
+#define NAND_CACHEPRG		0x00000008
+/* Chip has copy back function */
+#define NAND_COPYBACK		0x00000010
+/* AND Chip which has 4 banks and a confusing page / block 
+ * assignment. See Renesas datasheet for further information */
+#define NAND_IS_AND		0x00000020
+/* Chip has a array of 4 pages which can be read without
+ * additional ready /busy waits */
+#define NAND_4PAGE_ARRAY	0x00000040 
+		</programlisting>
+     		</para>
+     	</sect2>
+     	<sect2>   
+		<title>Constants for runtime options</title>
+     		<para>
+		These constants are defined in nand.h. They are ored together to describe
+		the functionality.
+     		<programlisting>
+/* Use a flash based bad block table. This option is parsed by the
+ * default bad block table function (nand_default_bbt). */
+#define NAND_USE_FLASH_BBT	0x00010000
+/* The hw ecc generator provides a syndrome instead a ecc value on read 
+ * This can only work if we have the ecc bytes directly behind the 
+ * data bytes. Applies for DOC and AG-AND Renesas HW Reed Solomon generators */
+#define NAND_HWECC_SYNDROME	0x00020000
+		</programlisting>
+     		</para>
+     	</sect2>
+     </sect1>	
+
+     <sect1>   
+	<title>ECC selection constants</title>
+	<para>
+	Use these constants to select the ECC algorithm.
+  	<programlisting>
+/* No ECC. Usage is not recommended ! */
+#define NAND_ECC_NONE		0
+/* Software ECC 3 byte ECC per 256 Byte data */
+#define NAND_ECC_SOFT		1
+/* Hardware ECC 3 byte ECC per 256 Byte data */
+#define NAND_ECC_HW3_256	2
+/* Hardware ECC 3 byte ECC per 512 Byte data */
+#define NAND_ECC_HW3_512	3
+/* Hardware ECC 6 byte ECC per 512 Byte data */
+#define NAND_ECC_HW6_512	4
+/* Hardware ECC 6 byte ECC per 512 Byte data */
+#define NAND_ECC_HW8_512	6
+	</programlisting>
+	</para>
+     </sect1>	
+
+     <sect1>   
+	<title>Hardware control related constants</title>
+	<para>
+	These constants describe the requested hardware access function when
+	the boardspecific hardware control function is called
+  	<programlisting>
+/* Select the chip by setting nCE to low */
+#define NAND_CTL_SETNCE 	1
+/* Deselect the chip by setting nCE to high */
+#define NAND_CTL_CLRNCE		2
+/* Select the command latch by setting CLE to high */
+#define NAND_CTL_SETCLE		3
+/* Deselect the command latch by setting CLE to low */
+#define NAND_CTL_CLRCLE		4
+/* Select the address latch by setting ALE to high */
+#define NAND_CTL_SETALE		5
+/* Deselect the address latch by setting ALE to low */
+#define NAND_CTL_CLRALE		6
+/* Set write protection by setting WP to high. Not used! */
+#define NAND_CTL_SETWP		7
+/* Clear write protection by setting WP to low. Not used! */
+#define NAND_CTL_CLRWP		8
+	</programlisting>
+	</para>
+     </sect1>	
+
+     <sect1>   
+	<title>Bad block table related constants</title>
+	<para>
+	These constants describe the options used for bad block
+	table descriptors.
+  	<programlisting>
+/* Options for the bad block table descriptors */
+
+/* The number of bits used per block in the bbt on the device */
+#define NAND_BBT_NRBITS_MSK	0x0000000F
+#define NAND_BBT_1BIT		0x00000001
+#define NAND_BBT_2BIT		0x00000002
+#define NAND_BBT_4BIT		0x00000004
+#define NAND_BBT_8BIT		0x00000008
+/* The bad block table is in the last good block of the device */
+#define	NAND_BBT_LASTBLOCK	0x00000010
+/* The bbt is at the given page, else we must scan for the bbt */
+#define NAND_BBT_ABSPAGE	0x00000020
+/* The bbt is at the given page, else we must scan for the bbt */
+#define NAND_BBT_SEARCH		0x00000040
+/* bbt is stored per chip on multichip devices */
+#define NAND_BBT_PERCHIP	0x00000080
+/* bbt has a version counter at offset veroffs */
+#define NAND_BBT_VERSION	0x00000100
+/* Create a bbt if none axists */
+#define NAND_BBT_CREATE		0x00000200
+/* Search good / bad pattern through all pages of a block */
+#define NAND_BBT_SCANALLPAGES	0x00000400
+/* Scan block empty during good / bad block scan */
+#define NAND_BBT_SCANEMPTY	0x00000800
+/* Write bbt if neccecary */
+#define NAND_BBT_WRITE		0x00001000
+/* Read and write back block contents when writing bbt */
+#define NAND_BBT_SAVECONTENT	0x00002000
+	</programlisting>
+	</para>
+     </sect1>	
+
+  </chapter>
+  	
+  <chapter id="structs">
+     <title>Structures</title>
+     <para>
+     This chapter contains the autogenerated documentation of the structures which are
+     used in the NAND driver and might be relevant for a driver developer. Each  
+     struct member has a short description which is marked with an [XXX] identifier.
+     See the chapter "Documentation hints" for an explanation.
+     </para>
+!Iinclude/linux/mtd/nand.h
+  </chapter>
+
+  <chapter id="pubfunctions">
+     <title>Public Functions Provided</title>
+     <para>
+     This chapter contains the autogenerated documentation of the NAND kernel API functions
+      which are exported. Each function has a short description which is marked with an [XXX] identifier.
+     See the chapter "Documentation hints" for an explanation.
+     </para>
+!Edrivers/mtd/nand/nand_base.c
+!Edrivers/mtd/nand/nand_bbt.c
+!Edrivers/mtd/nand/nand_ecc.c
+  </chapter>
+  
+  <chapter id="intfunctions">
+     <title>Internal Functions Provided</title>
+     <para>
+     This chapter contains the autogenerated documentation of the NAND driver internal functions.
+     Each function has a short description which is marked with an [XXX] identifier.
+     See the chapter "Documentation hints" for an explanation.
+     The functions marked with [DEFAULT] might be relevant for a board driver developer.
+     </para>
+!Idrivers/mtd/nand/nand_base.c
+!Idrivers/mtd/nand/nand_bbt.c
+!Idrivers/mtd/nand/nand_ecc.c
+  </chapter>
+
+  <chapter id="credits">
+     <title>Credits</title>
+	<para>
+		The following people have contributed to the NAND driver:
+		<orderedlist>
+			<listitem><para>Steven J. Hill<email>sjhill@realitydiluted.com</email></para></listitem>
+			<listitem><para>David Woodhouse<email>dwmw2@infradead.org</email></para></listitem>
+			<listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem>
+		</orderedlist>
+		A lot of users have provided bugfixes, improvements and helping hands for testing.
+		Thanks a lot.
+	</para>
+	<para>
+		The following people have contributed to this document:
+		<orderedlist>
+			<listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem>
+		</orderedlist>
+	</para>
+  </chapter>
+</book>
diff --git a/Documentation/DocBook/procfs-guide.tmpl b/Documentation/DocBook/procfs-guide.tmpl
new file mode 100644
index 000000000000..45cad23efefa
--- /dev/null
+++ b/Documentation/DocBook/procfs-guide.tmpl
@@ -0,0 +1,591 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
+<!ENTITY procfsexample SYSTEM "procfs_example.xml">
+]>
+
+<book id="LKProcfsGuide">
+  <bookinfo>
+    <title>Linux Kernel Procfs Guide</title>
+
+    <authorgroup>
+      <author>
+	<firstname>Erik</firstname>
+	<othername>(J.A.K.)</othername>
+	<surname>Mouw</surname>
+	<affiliation>
+	  <orgname>Delft University of Technology</orgname>
+	  <orgdiv>Faculty of Information Technology and Systems</orgdiv>
+	  <address>
+            <email>J.A.K.Mouw@its.tudelft.nl</email>
+            <pob>PO BOX 5031</pob>
+            <postcode>2600 GA</postcode>
+            <city>Delft</city>
+            <country>The Netherlands</country>
+          </address>
+	</affiliation>
+      </author>
+    </authorgroup>
+
+    <revhistory>
+      <revision>
+	<revnumber>1.0&nbsp;</revnumber>
+	<date>May 30, 2001</date>
+	<revremark>Initial revision posted to linux-kernel</revremark>
+      </revision>
+      <revision>
+	<revnumber>1.1&nbsp;</revnumber>
+	<date>June 3, 2001</date>
+	<revremark>Revised after comments from linux-kernel</revremark>
+      </revision>
+    </revhistory>
+
+    <copyright>
+      <year>2001</year>
+      <holder>Erik Mouw</holder>
+    </copyright>
+
+
+    <legalnotice>
+      <para>
+        This documentation is free software; you can redistribute it
+        and/or modify it under the terms of the GNU General Public
+        License as published by the Free Software Foundation; either
+        version 2 of the License, or (at your option) any later
+        version.
+      </para>
+      
+      <para>
+        This documentation is distributed in the hope that it will be
+        useful, but WITHOUT ANY WARRANTY; without even the implied
+        warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+        PURPOSE.  See the GNU General Public License for more details.
+      </para>
+      
+      <para>
+        You should have received a copy of the GNU General Public
+        License along with this program; if not, write to the Free
+        Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+        MA 02111-1307 USA
+      </para>
+      
+      <para>
+        For more details see the file COPYING in the source
+        distribution of Linux.
+      </para>
+    </legalnotice>
+  </bookinfo>
+
+
+
+
+  <toc>
+  </toc>
+
+
+
+
+  <preface>
+    <title>Preface</title>
+
+    <para>
+      This guide describes the use of the procfs file system from
+      within the Linux kernel. The idea to write this guide came up on
+      the #kernelnewbies IRC channel (see <ulink
+      url="http://www.kernelnewbies.org/">http://www.kernelnewbies.org/</ulink>),
+      when Jeff Garzik explained the use of procfs and forwarded me a
+      message Alexander Viro wrote to the linux-kernel mailing list. I
+      agreed to write it up nicely, so here it is.
+    </para>
+
+    <para>
+      I'd like to thank Jeff Garzik
+      <email>jgarzik@pobox.com</email> and Alexander Viro
+      <email>viro@parcelfarce.linux.theplanet.co.uk</email> for their input,
+      Tim Waugh <email>twaugh@redhat.com</email> for his <ulink
+      url="http://people.redhat.com/twaugh/docbook/selfdocbook/">Selfdocbook</ulink>,
+      and Marc Joosen <email>marcj@historia.et.tudelft.nl</email> for
+      proofreading.
+    </para>
+
+    <para>
+      This documentation was written while working on the LART
+      computing board (<ulink
+      url="http://www.lart.tudelft.nl/">http://www.lart.tudelft.nl/</ulink>),
+      which is sponsored by the Mobile Multi-media Communications
+      (<ulink
+      url="http://www.mmc.tudelft.nl/">http://www.mmc.tudelft.nl/</ulink>)
+      and Ubiquitous Communications (<ulink
+      url="http://www.ubicom.tudelft.nl/">http://www.ubicom.tudelft.nl/</ulink>)
+      projects.
+    </para>
+
+    <para>
+      Erik
+    </para>
+  </preface>
+
+
+
+
+  <chapter id="intro">
+    <title>Introduction</title>
+
+    <para>
+      The <filename class="directory">/proc</filename> file system
+      (procfs) is a special file system in the linux kernel. It's a
+      virtual file system: it is not associated with a block device
+      but exists only in memory. The files in the procfs are there to
+      allow userland programs access to certain information from the
+      kernel (like process information in <filename
+      class="directory">/proc/[0-9]+/</filename>), but also for debug
+      purposes (like <filename>/proc/ksyms</filename>).
+    </para>
+
+    <para>
+      This guide describes the use of the procfs file system from
+      within the Linux kernel. It starts by introducing all relevant
+      functions to manage the files within the file system. After that
+      it shows how to communicate with userland, and some tips and
+      tricks will be pointed out. Finally a complete example will be
+      shown.
+    </para>
+
+    <para>
+      Note that the files in <filename
+      class="directory">/proc/sys</filename> are sysctl files: they
+      don't belong to procfs and are governed by a completely
+      different API described in the Kernel API book.
+    </para>
+  </chapter>
+
+
+
+
+  <chapter id="managing">
+    <title>Managing procfs entries</title>
+    
+    <para>
+      This chapter describes the functions that various kernel
+      components use to populate the procfs with files, symlinks,
+      device nodes, and directories.
+    </para>
+
+    <para>
+      A minor note before we start: if you want to use any of the
+      procfs functions, be sure to include the correct header file! 
+      This should be one of the first lines in your code:
+    </para>
+
+    <programlisting>
+#include &lt;linux/proc_fs.h&gt;
+    </programlisting>
+
+
+
+
+    <sect1 id="regularfile">
+      <title>Creating a regular file</title>
+      
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>struct proc_dir_entry* <function>create_proc_entry</function></funcdef>
+	  <paramdef>const char* <parameter>name</parameter></paramdef>
+	  <paramdef>mode_t <parameter>mode</parameter></paramdef>
+	  <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+
+      <para>
+        This function creates a regular file with the name
+        <parameter>name</parameter>, file mode
+        <parameter>mode</parameter> in the directory
+        <parameter>parent</parameter>. To create a file in the root of
+        the procfs, use <constant>NULL</constant> as
+        <parameter>parent</parameter> parameter. When successful, the
+        function will return a pointer to the freshly created
+        <structname>struct proc_dir_entry</structname>; otherwise it
+        will return <constant>NULL</constant>. <xref
+        linkend="userland"/> describes how to do something useful with
+        regular files.
+      </para>
+
+      <para>
+        Note that it is specifically supported that you can pass a
+        path that spans multiple directories. For example
+        <function>create_proc_entry</function>(<parameter>"drivers/via0/info"</parameter>)
+        will create the <filename class="directory">via0</filename>
+        directory if necessary, with standard
+        <constant>0755</constant> permissions.
+      </para>
+
+    <para>
+      If you only want to be able to read the file, the function
+      <function>create_proc_read_entry</function> described in <xref
+      linkend="convenience"/> may be used to create and initialise
+      the procfs entry in one single call.
+    </para>
+    </sect1>
+
+
+
+
+    <sect1>
+      <title>Creating a symlink</title>
+
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>struct proc_dir_entry*
+	  <function>proc_symlink</function></funcdef> <paramdef>const
+	  char* <parameter>name</parameter></paramdef>
+	  <paramdef>struct proc_dir_entry*
+	  <parameter>parent</parameter></paramdef> <paramdef>const
+	  char* <parameter>dest</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+      
+      <para>
+        This creates a symlink in the procfs directory
+        <parameter>parent</parameter> that points from
+        <parameter>name</parameter> to
+        <parameter>dest</parameter>. This translates in userland to
+        <literal>ln -s</literal> <parameter>dest</parameter>
+        <parameter>name</parameter>.
+      </para>
+    </sect1>
+
+    <sect1>
+      <title>Creating a directory</title>
+      
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>struct proc_dir_entry* <function>proc_mkdir</function></funcdef>
+	  <paramdef>const char* <parameter>name</parameter></paramdef>
+	  <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+
+      <para>
+        Create a directory <parameter>name</parameter> in the procfs
+        directory <parameter>parent</parameter>.
+      </para>
+    </sect1>
+
+
+
+
+    <sect1>
+      <title>Removing an entry</title>
+      
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>void <function>remove_proc_entry</function></funcdef>
+	  <paramdef>const char* <parameter>name</parameter></paramdef>
+	  <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+
+      <para>
+        Removes the entry <parameter>name</parameter> in the directory
+        <parameter>parent</parameter> from the procfs. Entries are
+        removed by their <emphasis>name</emphasis>, not by the
+        <structname>struct proc_dir_entry</structname> returned by the
+        various create functions. Note that this function doesn't
+        recursively remove entries.
+      </para>
+
+      <para>
+        Be sure to free the <structfield>data</structfield> entry from
+        the <structname>struct proc_dir_entry</structname> before
+        <function>remove_proc_entry</function> is called (that is: if
+        there was some <structfield>data</structfield> allocated, of
+        course). See <xref linkend="usingdata"/> for more information
+        on using the <structfield>data</structfield> entry.
+      </para>
+    </sect1>
+  </chapter>
+
+
+
+
+  <chapter id="userland">
+    <title>Communicating with userland</title>
+    
+    <para>
+       Instead of reading (or writing) information directly from
+       kernel memory, procfs works with <emphasis>call back
+       functions</emphasis> for files: functions that are called when
+       a specific file is being read or written. Such functions have
+       to be initialised after the procfs file is created by setting
+       the <structfield>read_proc</structfield> and/or
+       <structfield>write_proc</structfield> fields in the
+       <structname>struct proc_dir_entry*</structname> that the
+       function <function>create_proc_entry</function> returned:
+    </para>
+
+    <programlisting>
+struct proc_dir_entry* entry;
+
+entry->read_proc = read_proc_foo;
+entry->write_proc = write_proc_foo;
+    </programlisting>
+
+    <para>
+      If you only want to use a the
+      <structfield>read_proc</structfield>, the function
+      <function>create_proc_read_entry</function> described in <xref
+      linkend="convenience"/> may be used to create and initialise the
+      procfs entry in one single call.
+    </para>
+
+
+
+    <sect1>
+      <title>Reading data</title>
+
+      <para>
+        The read function is a call back function that allows userland
+        processes to read data from the kernel. The read function
+        should have the following format:
+      </para>
+
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>int <function>read_func</function></funcdef>
+	  <paramdef>char* <parameter>page</parameter></paramdef>
+	  <paramdef>char** <parameter>start</parameter></paramdef>
+	  <paramdef>off_t <parameter>off</parameter></paramdef>
+	  <paramdef>int <parameter>count</parameter></paramdef>
+	  <paramdef>int* <parameter>eof</parameter></paramdef>
+	  <paramdef>void* <parameter>data</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+
+      <para>
+        The read function should write its information into the
+        <parameter>page</parameter>. For proper use, the function
+        should start writing at an offset of
+        <parameter>off</parameter> in <parameter>page</parameter> and
+        write at most <parameter>count</parameter> bytes, but because
+        most read functions are quite simple and only return a small
+        amount of information, these two parameters are usually
+        ignored (it breaks pagers like <literal>more</literal> and
+        <literal>less</literal>, but <literal>cat</literal> still
+        works).
+      </para>
+
+      <para>
+        If the <parameter>off</parameter> and
+        <parameter>count</parameter> parameters are properly used,
+        <parameter>eof</parameter> should be used to signal that the
+        end of the file has been reached by writing
+        <literal>1</literal> to the memory location
+        <parameter>eof</parameter> points to.
+      </para>
+
+      <para>
+        The parameter <parameter>start</parameter> doesn't seem to be
+        used anywhere in the kernel. The <parameter>data</parameter>
+        parameter can be used to create a single call back function for
+        several files, see <xref linkend="usingdata"/>.
+      </para>
+
+      <para>
+        The <function>read_func</function> function must return the
+        number of bytes written into the <parameter>page</parameter>.
+      </para>
+
+      <para>
+        <xref linkend="example"/> shows how to use a read call back
+        function.
+      </para>
+    </sect1>
+
+
+
+
+    <sect1>
+      <title>Writing data</title>
+
+      <para>
+        The write call back function allows a userland process to write
+        data to the kernel, so it has some kind of control over the
+        kernel. The write function should have the following format:
+      </para>
+
+      <funcsynopsis>
+	<funcprototype>
+	  <funcdef>int <function>write_func</function></funcdef>
+	  <paramdef>struct file* <parameter>file</parameter></paramdef>
+	  <paramdef>const char* <parameter>buffer</parameter></paramdef>
+	  <paramdef>unsigned long <parameter>count</parameter></paramdef>
+	  <paramdef>void* <parameter>data</parameter></paramdef>
+	</funcprototype>
+      </funcsynopsis>
+
+      <para>
+        The write function should read <parameter>count</parameter>
+        bytes at maximum from the <parameter>buffer</parameter>. Note
+        that the <parameter>buffer</parameter> doesn't live in the
+        kernel's memory space, so it should first be copied to kernel
+        space with <function>copy_from_user</function>. The
+        <parameter>file</parameter> parameter is usually
+        ignored. <xref linkend="usingdata"/> shows how to use the
+        <parameter>data</parameter> parameter.
+      </para>
+
+      <para>
+        Again, <xref linkend="example"/> shows how to use this call back
+        function.
+      </para>
+    </sect1>
+
+
+
+
+    <sect1 id="usingdata">
+      <title>A single call back for many files</title>
+
+      <para>
+         When a large number of almost identical files is used, it's
+         quite inconvenient to use a separate call back function for
+         each file. A better approach is to have a single call back
+         function that distinguishes between the files by using the
+         <structfield>data</structfield> field in <structname>struct
+         proc_dir_entry</structname>. First of all, the
+         <structfield>data</structfield> field has to be initialised:
+      </para>
+
+      <programlisting>
+struct proc_dir_entry* entry;
+struct my_file_data *file_data;
+
+file_data = kmalloc(sizeof(struct my_file_data), GFP_KERNEL);
+entry->data = file_data;
+      </programlisting>
+     
+      <para>
+          The <structfield>data</structfield> field is a <type>void
+          *</type>, so it can be initialised with anything.
+      </para>
+
+      &l