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Amiga filesystems Overview

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

Not all varieties of the Amiga filesystems are supported for reading and

writing. The Amiga currently knows 6 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 with 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.

uid[=uid]       This sets the uid of the root directory (i. e. the mount point

                to uid or to the uid of the current user, if the =uid is

                omitted.

gid[=gid]       Same as above, but for gid.

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. 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.

prefix=path     Path will be prefixed to every absolute path name of

                symbolic links on an AFFS partition. Default = /

volume=name     When symbolic links with an absolute path are created

                on an AFFS partition, volume will be prepended as the

                volume name. Default = "" (empty string).

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.

  - If both R and S are set, x will be set.

  - H, P and E are always retained and ignored under Linux.

  - A is always reset when written.

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.

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 S 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 (i. e. 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,reserved=4

    mount  /dev/sda3 /Amiga -t affs

/etc/fstab example

    /dev/sdb5   /d/f    affs    ro

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.

Filenames are truncated to 30 characters without warning.

Currently there are no checks against invalid characters (':')

in filenames.

Case is ignored by the affs in filename matching, but Linux shells

do care about the case. Example (with /mnt being an affs mounted fs):

    rm /mnt/WRONGCASE

will remove /mnt/wrongcase, but

    rm /mnt/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.

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 this without an Amiga (disk validator) or manually

(who would do this?). Maybe later.

A fsck.affs and mkfs.affs will probably be available in the future.

Until then, you should do

    ln -s /bin/true /etc/fs/mkfs.affs

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