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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.

Example:

You mount all your Amiga partitions under /amiga/ (where

 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

"/amiga/User/sc/include/dos/dos.h".

Examples

========

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

IMPORTANT NOTE

==============

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  is the device name).

DO AT YOUR OWN RISK:

  dd if=/dev/ 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/

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

fs/affs/Changes.

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

http://www-users.informatik.rwth-aachen.de/~crux/uae.html