|author||Borislav Petkov <email@example.com>||2008-02-02 19:56:48 +0100|
|committer||Bartlomiej Zolnierkiewicz <firstname.lastname@example.org>||2008-02-02 19:56:48 +0100|
ide-tape: move historical changelog to Documentation/ide/ChangeLog.ide-tape.1995-2002
Also, cleanup whitespace and update comments. Bart: - remove reference to drivers/block/ide.c - move driver documentation to Documentation/ide/ide-tape.txt Signed-off-by: Borislav Petkov <email@example.com> Signed-off-by: Bartlomiej Zolnierkiewicz <firstname.lastname@example.org>
Diffstat (limited to 'Documentation/ide')
2 files changed, 403 insertions, 0 deletions
diff --git a/Documentation/ide/ChangeLog.ide-tape.1995-2002 b/Documentation/ide/ChangeLog.ide-tape.1995-2002
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+ * Ver 0.1 Nov 1 95 Pre-working code :-)
+ * Ver 0.2 Nov 23 95 A short backup (few megabytes) and restore procedure
+ * was successful ! (Using tar cvf ... on the block
+ * device interface).
+ * A longer backup resulted in major swapping, bad
+ * overall Linux performance and eventually failed as
+ * we received non serial read-ahead requests from the
+ * buffer cache.
+ * Ver 0.3 Nov 28 95 Long backups are now possible, thanks to the
+ * character device interface. Linux's responsiveness
+ * and performance doesn't seem to be much affected
+ * from the background backup procedure.
+ * Some general mtio.h magnetic tape operations are
+ * now supported by our character device. As a result,
+ * popular tape utilities are starting to work with
+ * ide tapes :-)
+ * The following configurations were tested:
+ * 1. An IDE ATAPI TAPE shares the same interface
+ * and irq with an IDE ATAPI CDROM.
+ * 2. An IDE ATAPI TAPE shares the same interface
+ * and irq with a normal IDE disk.
+ * Both configurations seemed to work just fine !
+ * However, to be on the safe side, it is meanwhile
+ * recommended to give the IDE TAPE its own interface
+ * and irq.
+ * The one thing which needs to be done here is to
+ * add a "request postpone" feature to ide.c,
+ * so that we won't have to wait for the tape to finish
+ * performing a long media access (DSC) request (such
+ * as a rewind) before we can access the other device
+ * on the same interface. This effect doesn't disturb
+ * normal operation most of the time because read/write
+ * requests are relatively fast, and once we are
+ * performing one tape r/w request, a lot of requests
+ * from the other device can be queued and ide.c will
+ * service all of them after this single tape request.
+ * Ver 1.0 Dec 11 95 Integrated into Linux 1.3.46 development tree.
+ * On each read / write request, we now ask the drive
+ * if we can transfer a constant number of bytes
+ * (a parameter of the drive) only to its buffers,
+ * without causing actual media access. If we can't,
+ * we just wait until we can by polling the DSC bit.
+ * This ensures that while we are not transferring
+ * more bytes than the constant referred to above, the
+ * interrupt latency will not become too high and
+ * we won't cause an interrupt timeout, as happened
+ * occasionally in the previous version.
+ * While polling for DSC, the current request is
+ * postponed and ide.c is free to handle requests from
+ * the other device. This is handled transparently to
+ * ide.c. The hwgroup locking method which was used
+ * in the previous version was removed.
+ * Use of new general features which are provided by
+ * ide.c for use with atapi devices.
+ * (Programming done by Mark Lord)
+ * Few potential bug fixes (Again, suggested by Mark)
+ * Single character device data transfers are now
+ * not limited in size, as they were before.
+ * We are asking the tape about its recommended
+ * transfer unit and send a larger data transfer
+ * as several transfers of the above size.
+ * For best results, use an integral number of this
+ * basic unit (which is shown during driver
+ * initialization). I will soon add an ioctl to get
+ * this important parameter.
+ * Our data transfer buffer is allocated on startup,
+ * rather than before each data transfer. This should
+ * ensure that we will indeed have a data buffer.
+ * Ver 1.1 Dec 14 95 Fixed random problems which occurred when the tape
+ * shared an interface with another device.
+ * (poll_for_dsc was a complete mess).
+ * Removed some old (non-active) code which had
+ * to do with supporting buffer cache originated
+ * requests.
+ * The block device interface can now be opened, so
+ * that general ide driver features like the unmask
+ * interrupts flag can be selected with an ioctl.
+ * This is the only use of the block device interface.
+ * New fast pipelined operation mode (currently only on
+ * writes). When using the pipelined mode, the
+ * throughput can potentially reach the maximum
+ * tape supported throughput, regardless of the
+ * user backup program. On my tape drive, it sometimes
+ * boosted performance by a factor of 2. Pipelined
+ * mode is enabled by default, but since it has a few
+ * downfalls as well, you may want to disable it.
+ * A short explanation of the pipelined operation mode
+ * is available below.
+ * Ver 1.2 Jan 1 96 Eliminated pipelined mode race condition.
+ * Added pipeline read mode. As a result, restores
+ * are now as fast as backups.
+ * Optimized shared interface behavior. The new behavior
+ * typically results in better IDE bus efficiency and
+ * higher tape throughput.
+ * Pre-calculation of the expected read/write request
+ * service time, based on the tape's parameters. In
+ * the pipelined operation mode, this allows us to
+ * adjust our polling frequency to a much lower value,
+ * and thus to dramatically reduce our load on Linux,
+ * without any decrease in performance.
+ * Implemented additional mtio.h operations.
+ * The recommended user block size is returned by
+ * the MTIOCGET ioctl.
+ * Additional minor changes.
+ * Ver 1.3 Feb 9 96 Fixed pipelined read mode bug which prevented the
+ * use of some block sizes during a restore procedure.
+ * The character device interface will now present a
+ * continuous view of the media - any mix of block sizes
+ * during a backup/restore procedure is supported. The
+ * driver will buffer the requests internally and
+ * convert them to the tape's recommended transfer
+ * unit, making performance almost independent of the
+ * chosen user block size.
+ * Some improvements in error recovery.
+ * By cooperating with ide-dma.c, bus mastering DMA can
+ * now sometimes be used with IDE tape drives as well.
+ * Bus mastering DMA has the potential to dramatically
+ * reduce the CPU's overhead when accessing the device,
+ * and can be enabled by using hdparm -d1 on the tape's
+ * block device interface. For more info, read the
+ * comments in ide-dma.c.
+ * Ver 1.4 Mar 13 96 Fixed serialize support.
+ * Ver 1.5 Apr 12 96 Fixed shared interface operation, broken in 1.3.85.
+ * Fixed pipelined read mode inefficiency.
+ * Fixed nasty null dereferencing bug.
+ * Ver 1.6 Aug 16 96 Fixed FPU usage in the driver.
+ * Fixed end of media bug.
+ * Ver 1.7 Sep 10 96 Minor changes for the CONNER CTT8000-A model.
+ * Ver 1.8 Sep 26 96 Attempt to find a better balance between good
+ * interactive response and high system throughput.
+ * Ver 1.9 Nov 5 96 Automatically cross encountered filemarks rather
+ * than requiring an explicit FSF command.
+ * Abort pending requests at end of media.
+ * MTTELL was sometimes returning incorrect results.
+ * Return the real block size in the MTIOCGET ioctl.
+ * Some error recovery bug fixes.
+ * Ver 1.10 Nov 5 96 Major reorganization.
+ * Reduced CPU overhead a bit by eliminating internal
+ * bounce buffers.
+ * Added module support.
+ * Added multiple tape drives support.
+ * Added partition support.
+ * Rewrote DSC handling.
+ * Some portability fixes.
+ * Removed ide-tape.h.
+ * Additional minor changes.
+ * Ver 1.11 Dec 2 96 Bug fix in previous DSC timeout handling.
+ * Use ide_stall_queue() for DSC overlap.
+ * Use the maximum speed rather than the current speed
+ * to compute the request service time.
+ * Ver 1.12 Dec 7 97 Fix random memory overwriting and/or last block data
+ * corruption, which could occur if the total number
+ * of bytes written to the tape was not an integral
+ * number of tape blocks.
+ * Add support for INTERRUPT DRQ devices.
+ * Ver 1.13 Jan 2 98 Add "speed == 0" work-around for HP COLORADO 5GB
+ * Ver 1.14 Dec 30 98 Partial fixes for the Sony/AIWA tape drives.
+ * Replace cli()/sti() with hwgroup spinlocks.
+ * Ver 1.15 Mar 25 99 Fix SMP race condition by replacing hwgroup
+ * spinlock with private per-tape spinlock.
+ * Ver 1.16 Sep 1 99 Add OnStream tape support.
+ * Abort read pipeline on EOD.
+ * Wait for the tape to become ready in case it returns
+ * "in the process of becoming ready" on open().
+ * Fix zero padding of the last written block in
+ * case the tape block size is larger than PAGE_SIZE.
+ * Decrease the default disconnection time to tn.
+ * Ver 1.16e Oct 3 99 Minor fixes.
+ * Ver 1.16e1 Oct 13 99 Patches by Arnold Niessen,
+ * email@example.com / firstname.lastname@example.org
+ * GO-1) Undefined code in idetape_read_position
+ * according to Gadi's email
+ * AJN-1) Minor fix asc == 11 should be asc == 0x11
+ * in idetape_issue_packet_command (did effect
+ * debugging output only)
+ * AJN-2) Added more debugging output, and
+ * added ide-tape: where missing. I would also
+ * like to add tape->name where possible
+ * AJN-3) Added different debug_level's
+ * via /proc/ide/hdc/settings
+ * "debug_level" determines amount of debugging output;
+ * can be changed using /proc/ide/hdx/settings
+ * 0 : almost no debugging output
+ * 1 : 0+output errors only
+ * 2 : 1+output all sensekey/asc
+ * 3 : 2+follow all chrdev related procedures
+ * 4 : 3+follow all procedures
+ * 5 : 4+include pc_stack rq_stack info
+ * 6 : 5+USE_COUNT updates
+ * AJN-4) Fixed timeout for retension in idetape_queue_pc_tail
+ * from 5 to 10 minutes
+ * AJN-5) Changed maximum number of blocks to skip when
+ * reading tapes with multiple consecutive write
+ * errors from 100 to 1000 in idetape_get_logical_blk
+ * Proposed changes to code:
+ * 1) output "logical_blk_num" via /proc
+ * 2) output "current_operation" via /proc
+ * 3) Either solve or document the fact that `mt rewind' is
+ * required after reading from /dev/nhtx to be
+ * able to rmmod the idetape module;
+ * Also, sometimes an application finishes but the
+ * device remains `busy' for some time. Same cause ?
+ * Proposed changes to release-notes:
+ * 4) write a simple `quickstart' section in the
+ * release notes; I volunteer if you don't want to
+ * 5) include a pointer to video4linux in the doc
+ * to stimulate video applications
+ * 6) release notes lines 331 and 362: explain what happens
+ * if the application data rate is higher than 1100 KB/s;
+ * similar approach to lower-than-500 kB/s ?
+ * 7) 6.6 Comparison; wouldn't it be better to allow different
+ * strategies for read and write ?
+ * Wouldn't it be better to control the tape buffer
+ * contents instead of the bandwidth ?
+ * 8) line 536: replace will by would (if I understand
+ * this section correctly, a hypothetical and unwanted situation
+ * is being described)
+ * Ver 1.16f Dec 15 99 Change place of the secondary OnStream header frames.
+ * Ver 1.17 Nov 2000 / Jan 2001 Marcel Mol, email@example.com
+ * - Add idetape_onstream_mode_sense_tape_parameter_page
+ * function to get tape capacity in frames: tape->capacity.
+ * - Add support for DI-50 drives( or any DI- drive).
+ * - 'workaround' for read error/blank block around block 3000.
+ * - Implement Early warning for end of media for Onstream.
+ * - Cosmetic code changes for readability.
+ * - Idetape_position_tape should not use SKIP bit during
+ * Onstream read recovery.
+ * - Add capacity, logical_blk_num and first/last_frame_position
+ * to /proc/ide/hd?/settings.
+ * - Module use count was gone in the Linux 2.4 driver.
+ * Ver 1.17a Apr 2001 Willem Riede firstname.lastname@example.org
+ * - Get drive's actual block size from mode sense block descriptor
+ * - Limit size of pipeline
+ * Ver 1.17b Oct 2002 Alan Stern <email@example.com>
+ * Changed IDETAPE_MIN_PIPELINE_STAGES to 1 and actually used
+ * it in the code!
+ * Actually removed aborted stages in idetape_abort_pipeline
+ * instead of just changing the command code.
+ * Made the transfer byte count for Request Sense equal to the
+ * actual length of the data transfer.
+ * Changed handling of partial data transfers: they do not
+ * cause DMA errors.
+ * Moved initiation of DMA transfers to the correct place.
+ * Removed reference to unallocated memory.
+ * Made __idetape_discard_read_pipeline return the number of
+ * sectors skipped, not the number of stages.
+ * Replaced errant kfree() calls with __idetape_kfree_stage().
+ * Fixed off-by-one error in testing the pipeline length.
+ * Fixed handling of filemarks in the read pipeline.
+ * Small code optimization for MTBSF and MTBSFM ioctls.
+ * Don't try to unlock the door during device close if is
+ * already unlocked!
+ * Cosmetic fixes to miscellaneous debugging output messages.
+ * Set the minimum /proc/ide/hd?/settings values for "pipeline",
+ * "pipeline_min", and "pipeline_max" to 1.
diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt
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+ * IDE ATAPI streaming tape driver.
+ * This driver is a part of the Linux ide driver.
+ * The driver, in co-operation with ide.c, basically traverses the
+ * request-list for the block device interface. The character device
+ * interface, on the other hand, creates new requests, adds them
+ * to the request-list of the block device, and waits for their completion.
+ * Pipelined operation mode is now supported on both reads and writes.
+ * The block device major and minor numbers are determined from the
+ * tape's relative position in the ide interfaces, as explained in ide.c.
+ * The character device interface consists of the following devices:
+ * ht0 major 37, minor 0 first IDE tape, rewind on close.
+ * ht1 major 37, minor 1 second IDE tape, rewind on close.
+ * ...
+ * nht0 major 37, minor 128 first IDE tape, no rewind on close.
+ * nht1 major 37, minor 129 second IDE tape, no rewind on close.
+ * ...
+ * The general magnetic tape commands compatible interface, as defined by
+ * include/linux/mtio.h, is accessible through the character device.
+ * General ide driver configuration options, such as the interrupt-unmask
+ * flag, can be configured by issuing an ioctl to the block device interface,
+ * as any other ide device.
+ * Our own ide-tape ioctl's can be issued to either the block device or
+ * the character device interface.
+ * Maximal throughput with minimal bus load will usually be achieved in the
+ * following scenario:
+ * 1. ide-tape is operating in the pipelined operation mode.
+ * 2. No buffering is performed by the user backup program.
+ * Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive.
+ * Here are some words from the first releases of hd.c, which are quoted
+ * in ide.c and apply here as well:
+ * | Special care is recommended. Have Fun!
+ * An overview of the pipelined operation mode.
+ * In the pipelined write mode, we will usually just add requests to our
+ * pipeline and return immediately, before we even start to service them. The
+ * user program will then have enough time to prepare the next request while
+ * we are still busy servicing previous requests. In the pipelined read mode,
+ * the situation is similar - we add read-ahead requests into the pipeline,
+ * before the user even requested them.
+ * The pipeline can be viewed as a "safety net" which will be activated when
+ * the system load is high and prevents the user backup program from keeping up
+ * with the current tape speed. At this point, the pipeline will get
+ * shorter and shorter but the tape will still be streaming at the same speed.
+ * Assuming we have enough pipeline stages, the system load will hopefully
+ * decrease before the pipeline is completely empty, and the backup program
+ * will be able to "catch up" and refill the pipeline again.
+ * When using the pipelined mode, it would be best to disable any type of
+ * buffering done by the user program, as ide-tape already provides all the
+ * benefits in the kernel, where it can be done in a more efficient way.
+ * As we will usually not block the user program on a request, the most
+ * efficient user code will then be a simple read-write-read-... cycle.
+ * Any additional logic will usually just slow down the backup process.
+ * Using the pipelined mode, I get a constant over 400 KBps throughput,
+ * which seems to be the maximum throughput supported by my tape.
+ * However, there are some downfalls:
+ * 1. We use memory (for data buffers) in proportional to the number
+ * of pipeline stages (each stage is about 26 KB with my tape).
+ * 2. In the pipelined write mode, we cheat and postpone error codes
+ * to the user task. In read mode, the actual tape position
+ * will be a bit further than the last requested block.
+ * Concerning (1):
+ * 1. We allocate stages dynamically only when we need them. When
+ * we don't need them, we don't consume additional memory. In
+ * case we can't allocate stages, we just manage without them
+ * (at the expense of decreased throughput) so when Linux is
+ * tight in memory, we will not pose additional difficulties.
+ * 2. The maximum number of stages (which is, in fact, the maximum
+ * amount of memory) which we allocate is limited by the compile
+ * time parameter IDETAPE_MAX_PIPELINE_STAGES.
+ * 3. The maximum number of stages is a controlled parameter - We
+ * don't start from the user defined maximum number of stages
+ * but from the lower IDETAPE_MIN_PIPELINE_STAGES (again, we
+ * will not even allocate this amount of stages if the user
+ * program can't handle the speed). We then implement a feedback
+ * loop which checks if the pipeline is empty, and if it is, we
+ * increase the maximum number of stages as necessary until we
+ * reach the optimum value which just manages to keep the tape
+ * busy with minimum allocated memory or until we reach
+ * IDETAPE_MAX_PIPELINE_STAGES.
+ * Concerning (2):
+ * In pipelined write mode, ide-tape can not return accurate error codes
+ * to the user program since we usually just add the request to the
+ * pipeline without waiting for it to be serviced. In case an error
+ * occurs, I will report it on the next user request.
+ * In the pipelined read mode, subsequent read requests or forward
+ * filemark spacing will perform correctly, as we preserve all blocks
+ * and filemarks which we encountered during our excess read-ahead.
+ * For accurate tape positioning and error reporting, disabling
+ * pipelined mode might be the best option.
+ * You can enable/disable/tune the pipelined operation mode by adjusting
+ * the compile time parameters below.
+ * Possible improvements.
+ * 1. Support for the ATAPI overlap protocol.
+ * In order to maximize bus throughput, we currently use the DSC
+ * overlap method which enables ide.c to service requests from the
+ * other device while the tape is busy executing a command. The
+ * DSC overlap method involves polling the tape's status register
+ * for the DSC bit, and servicing the other device while the tape
+ * isn't ready.
+ * In the current QIC development standard (December 1995),
+ * it is recommended that new tape drives will *in addition*
+ * implement the ATAPI overlap protocol, which is used for the
+ * same purpose - efficient use of the IDE bus, but is interrupt
+ * driven and thus has much less CPU overhead.
+ * ATAPI overlap is likely to be supported in most new ATAPI
+ * devices, including new ATAPI cdroms, and thus provides us
+ * a method by which we can achieve higher throughput when
+ * sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.