path: root/Documentation/filesystems/affs.txt
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/filesystems/affs.txt
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!
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+Overview of Amiga Filesystems
+Not all varieties of the Amiga filesystems are supported for reading and
+writing. The Amiga currently knows six different filesystems:
+DOS\0 The old or original filesystem, not really suited for
+ hard disks and normally not used on them, either.
+ Supported read/write.
+DOS\1 The original Fast File System. Supported read/write.
+DOS\2 The old "international" filesystem. International means that
+ a bug has been fixed so that accented ("international") letters
+ in file names are case-insensitive, as they ought to be.
+ Supported read/write.
+DOS\3 The "international" Fast File System. Supported read/write.
+DOS\4 The original filesystem with directory cache. The directory
+ cache speeds up directory accesses on floppies considerably,
+ but slows down file creation/deletion. Doesn't make much
+ sense on hard disks. Supported read only.
+DOS\5 The Fast File System with directory cache. Supported read only.
+All of the above filesystems allow block sizes from 512 to 32K bytes.
+Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks
+speed up almost everything at the expense of wasted disk space. The speed
+gain above 4K seems not really worth the price, so you don't lose too
+much here, either.
+The muFS (multi user File System) equivalents of the above file systems
+are supported, too.
+Mount options for the AFFS
+protect If this option is set, the protection bits cannot be altered.
+setuid[=uid] This sets the owner of all files and directories in the file
+ system to uid or the uid of the current user, respectively.
+setgid[=gid] Same as above, but for gid.
+mode=mode Sets the mode flags to the given (octal) value, regardless
+ of the original permissions. Directories will get an x
+ permission if the corresponding r bit is set.
+ This is useful since most of the plain AmigaOS files
+ will map to 600.
+reserved=num Sets the number of reserved blocks at the start of the
+ partition to num. You should never need this option.
+ Default is 2.
+root=block Sets the block number of the root block. This should never
+ be necessary.
+bs=blksize Sets the blocksize to blksize. Valid block sizes are 512,
+ 1024, 2048 and 4096. Like the root option, this should
+ never be necessary, as the affs can figure it out itself.
+quiet The file system will not return an error for disallowed
+ mode changes.
+verbose The volume name, file system type and block size will
+ be written to the syslog when the filesystem is mounted.
+mufs The filesystem is really a muFS, also it doesn't
+ identify itself as one. This option is necessary if
+ the filesystem wasn't formatted as muFS, but is used
+ as one.
+prefix=path Path will be prefixed to every absolute path name of
+ symbolic links on an AFFS partition. Default = "/".
+ (See below.)
+volume=name When symbolic links with an absolute path are created
+ on an AFFS partition, name will be prepended as the
+ volume name. Default = "" (empty string).
+ (See below.)
+Handling of the Users/Groups and protection flags
+Amiga -> Linux:
+The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
+ - R maps to r for user, group and others. On directories, R implies x.
+ - If both W and D are allowed, w will be set.
+ - E maps to x.
+ - H and P are always retained and ignored under Linux.
+ - A is always reset when a file is written to.
+User id and group id will be used unless set[gu]id are given as mount
+options. Since most of the Amiga file systems are single user systems
+they will be owned by root. The root directory (the mount point) of the
+Amiga filesystem will be owned by the user who actually mounts the
+filesystem (the root directory doesn't have uid/gid fields).
+Linux -> Amiga:
+The Linux rwxrwxrwx file mode is handled as follows:
+ - r permission will set R for user, group and others.
+ - w permission will set W and D for user, group and others.
+ - x permission of the user will set E for plain files.
+ - All other flags (suid, sgid, ...) are ignored and will
+ not be retained.
+Newly created files and directories will get the user and group ID
+of the current user and a mode according to the umask.
+Symbolic links
+Although the Amiga and Linux file systems resemble each other, there
+are some, not always subtle, differences. One of them becomes apparent
+with symbolic links. While Linux has a file system with exactly one
+root directory, the Amiga has a separate root directory for each
+file system (for example, partition, floppy disk, ...). With the Amiga,
+these entities are called "volumes". They have symbolic names which
+can be used to access them. Thus, symbolic links can point to a
+different volume. AFFS turns the volume name into a directory name
+and prepends the prefix path (see prefix option) to it.
+You mount all your Amiga partitions under /amiga/<volume> (where
+<volume> is the name of the volume), and you give the option
+"prefix=/amiga/" when mounting all your AFFS partitions. (They
+might be "User", "WB" and "Graphics", the mount points /amiga/User,
+/amiga/WB and /amiga/Graphics). A symbolic link referring to
+"User:sc/include/dos/dos.h" will be followed to
+Command line:
+ mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
+ mount /dev/sda3 /Amiga -t affs
+/etc/fstab entry:
+ /dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0
+If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
+have an Amiga harddisk connected to your PC, it will overwrite
+the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
+the Rigid Disk Block. Sheer luck has it that this is an unused
+area of the RDB, so only the checksum doesn't match anymore.
+Linux will ignore this garbage and recognize the RDB anyway, but
+before you connect that drive to your Amiga again, you must
+restore or repair your RDB. So please do make a backup copy of it
+before booting Windows!
+If the damage is already done, the following should fix the RDB
+(where <disk> is the device name).
+ dd if=/dev/<disk> of=rdb.tmp count=1
+ cp rdb.tmp rdb.fixed
+ dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4
+ dd if=rdb.fixed of=/dev/<disk>
+Bugs, Restrictions, Caveats
+Quite a few things may not work as advertised. Not everything is
+tested, though several hundred MB have been read and written using
+this fs. For a most up-to-date list of bugs please consult
+Filenames are truncated to 30 characters without warning (this
+can be changed by setting the compile-time option AFFS_NO_TRUNCATE
+in include/linux/amigaffs.h).
+Case is ignored by the affs in filename matching, but Linux shells
+do care about the case. Example (with /wb being an affs mounted fs):
+ rm /wb/WRONGCASE
+will remove /mnt/wrongcase, but
+ rm /wb/WR*
+will not since the names are matched by the shell.
+The block allocation is designed for hard disk partitions. If more
+than 1 process writes to a (small) diskette, the blocks are allocated
+in an ugly way (but the real AFFS doesn't do much better). This
+is also true when space gets tight.
+You cannot execute programs on an OFS (Old File System), since the
+program files cannot be memory mapped due to the 488 byte blocks.
+For the same reason you cannot mount an image on such a filesystem
+via the loopback device.
+The bitmap valid flag in the root block may not be accurate when the
+system crashes while an affs partition is mounted. There's currently
+no way to fix a garbled filesystem without an Amiga (disk validator)
+or manually (who would do this?). Maybe later.
+If you mount affs partitions on system startup, you may want to tell
+fsck that the fs should not be checked (place a '0' in the sixth field
+of /etc/fstab).
+It's not possible to read floppy disks with a normal PC or workstation
+due to an incompatibility with the Amiga floppy controller.
+If you are interested in an Amiga Emulator for Linux, look at