linux/Documentation/filesystems/affs.txt
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   1Overview of Amiga Filesystems
   2=============================
   3
   4Not all varieties of the Amiga filesystems are supported for reading and
   5writing. The Amiga currently knows six different filesystems:
   6
   7DOS\0           The old or original filesystem, not really suited for
   8                hard disks and normally not used on them, either.
   9                Supported read/write.
  10
  11DOS\1           The original Fast File System. Supported read/write.
  12
  13DOS\2           The old "international" filesystem. International means that
  14                a bug has been fixed so that accented ("international") letters
  15                in file names are case-insensitive, as they ought to be.
  16                Supported read/write.
  17
  18DOS\3           The "international" Fast File System.  Supported read/write.
  19
  20DOS\4           The original filesystem with directory cache. The directory
  21                cache speeds up directory accesses on floppies considerably,
  22                but slows down file creation/deletion. Doesn't make much
  23                sense on hard disks. Supported read only.
  24
  25DOS\5           The Fast File System with directory cache. Supported read only.
  26
  27All of the above filesystems allow block sizes from 512 to 32K bytes.
  28Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks
  29speed up almost everything at the expense of wasted disk space. The speed
  30gain above 4K seems not really worth the price, so you don't lose too
  31much here, either.
  32
  33The muFS (multi user File System) equivalents of the above file systems
  34are supported, too.
  35
  36Mount options for the AFFS
  37==========================
  38
  39protect         If this option is set, the protection bits cannot be altered.
  40
  41setuid[=uid]    This sets the owner of all files and directories in the file
  42                system to uid or the uid of the current user, respectively.
  43
  44setgid[=gid]    Same as above, but for gid.
  45
  46mode=mode       Sets the mode flags to the given (octal) value, regardless
  47                of the original permissions. Directories will get an x
  48                permission if the corresponding r bit is set.
  49                This is useful since most of the plain AmigaOS files
  50                will map to 600.
  51
  52reserved=num    Sets the number of reserved blocks at the start of the
  53                partition to num. You should never need this option.
  54                Default is 2.
  55
  56root=block      Sets the block number of the root block. This should never
  57                be necessary.
  58
  59bs=blksize      Sets the blocksize to blksize. Valid block sizes are 512,
  60                1024, 2048 and 4096. Like the root option, this should
  61                never be necessary, as the affs can figure it out itself.
  62
  63quiet           The file system will not return an error for disallowed
  64                mode changes.
  65
  66verbose         The volume name, file system type and block size will
  67                be written to the syslog when the filesystem is mounted.
  68
  69mufs            The filesystem is really a muFS, also it doesn't
  70                identify itself as one. This option is necessary if
  71                the filesystem wasn't formatted as muFS, but is used
  72                as one.
  73
  74prefix=path     Path will be prefixed to every absolute path name of
  75                symbolic links on an AFFS partition. Default = "/".
  76                (See below.)
  77
  78volume=name     When symbolic links with an absolute path are created
  79                on an AFFS partition, name will be prepended as the
  80                volume name. Default = "" (empty string).
  81                (See below.)
  82
  83Handling of the Users/Groups and protection flags
  84=================================================
  85
  86Amiga -> Linux:
  87
  88The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
  89
  90  - R maps to r for user, group and others. On directories, R implies x.
  91
  92  - If both W and D are allowed, w will be set.
  93
  94  - E maps to x.
  95
  96  - H and P are always retained and ignored under Linux.
  97
  98  - A is always reset when a file is written to.
  99
 100User id and group id will be used unless set[gu]id are given as mount
 101options. Since most of the Amiga file systems are single user systems
 102they will be owned by root. The root directory (the mount point) of the
 103Amiga filesystem will be owned by the user who actually mounts the
 104filesystem (the root directory doesn't have uid/gid fields).
 105
 106Linux -> Amiga:
 107
 108The Linux rwxrwxrwx file mode is handled as follows:
 109
 110  - r permission will set R for user, group and others.
 111
 112  - w permission will set W and D for user, group and others.
 113
 114  - x permission of the user will set E for plain files.
 115
 116  - All other flags (suid, sgid, ...) are ignored and will
 117    not be retained.
 118    
 119Newly created files and directories will get the user and group ID
 120of the current user and a mode according to the umask.
 121
 122Symbolic links
 123==============
 124
 125Although the Amiga and Linux file systems resemble each other, there
 126are some, not always subtle, differences. One of them becomes apparent
 127with symbolic links. While Linux has a file system with exactly one
 128root directory, the Amiga has a separate root directory for each
 129file system (for example, partition, floppy disk, ...). With the Amiga,
 130these entities are called "volumes". They have symbolic names which
 131can be used to access them. Thus, symbolic links can point to a
 132different volume. AFFS turns the volume name into a directory name
 133and prepends the prefix path (see prefix option) to it.
 134
 135Example:
 136You mount all your Amiga partitions under /amiga/<volume> (where
 137<volume> is the name of the volume), and you give the option
 138"prefix=/amiga/" when mounting all your AFFS partitions. (They
 139might be "User", "WB" and "Graphics", the mount points /amiga/User,
 140/amiga/WB and /amiga/Graphics). A symbolic link referring to
 141"User:sc/include/dos/dos.h" will be followed to
 142"/amiga/User/sc/include/dos/dos.h".
 143
 144Examples
 145========
 146
 147Command line:
 148    mount  Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
 149    mount  /dev/sda3 /Amiga -t affs
 150
 151/etc/fstab entry:
 152    /dev/sdb5   /amiga/Workbench    affs    noauto,user,exec,verbose 0 0
 153
 154IMPORTANT NOTE
 155==============
 156
 157If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
 158have an Amiga harddisk connected to your PC, it will overwrite
 159the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
 160the Rigid Disk Block. Sheer luck has it that this is an unused
 161area of the RDB, so only the checksum doesn't match anymore.
 162Linux will ignore this garbage and recognize the RDB anyway, but
 163before you connect that drive to your Amiga again, you must
 164restore or repair your RDB. So please do make a backup copy of it
 165before booting Windows!
 166
 167If the damage is already done, the following should fix the RDB
 168(where <disk> is the device name).
 169DO AT YOUR OWN RISK:
 170
 171  dd if=/dev/<disk> of=rdb.tmp count=1
 172  cp rdb.tmp rdb.fixed
 173  dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4
 174  dd if=rdb.fixed of=/dev/<disk>
 175
 176Bugs, Restrictions, Caveats
 177===========================
 178
 179Quite a few things may not work as advertised. Not everything is
 180tested, though several hundred MB have been read and written using
 181this fs. For a most up-to-date list of bugs please consult
 182fs/affs/Changes.
 183
 184Filenames are truncated to 30 characters without warning (this
 185can be changed by setting the compile-time option AFFS_NO_TRUNCATE
 186in include/linux/amigaffs.h).
 187
 188Case is ignored by the affs in filename matching, but Linux shells
 189do care about the case. Example (with /wb being an affs mounted fs):
 190    rm /wb/WRONGCASE
 191will remove /mnt/wrongcase, but
 192    rm /wb/WR*
 193will not since the names are matched by the shell.
 194
 195The block allocation is designed for hard disk partitions. If more
 196than 1 process writes to a (small) diskette, the blocks are allocated
 197in an ugly way (but the real AFFS doesn't do much better). This
 198is also true when space gets tight.
 199
 200You cannot execute programs on an OFS (Old File System), since the
 201program files cannot be memory mapped due to the 488 byte blocks.
 202For the same reason you cannot mount an image on such a filesystem
 203via the loopback device.
 204
 205The bitmap valid flag in the root block may not be accurate when the
 206system crashes while an affs partition is mounted. There's currently
 207no way to fix a garbled filesystem without an Amiga (disk validator)
 208or manually (who would do this?). Maybe later.
 209
 210If you mount affs partitions on system startup, you may want to tell
 211fsck that the fs should not be checked (place a '0' in the sixth field
 212of /etc/fstab).
 213
 214It's not possible to read floppy disks with a normal PC or workstation
 215due to an incompatibility with the Amiga floppy controller.
 216
 217If you are interested in an Amiga Emulator for Linux, look at
 218
 219http://web.archive.org/web/*/http://www.freiburg.linux.de/~uae/
 220
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