Documentation/filesystems/affs.rst - linux/kernel/git/dtor/input - Git at Google


            
            .. SPDX-License-Identifier: GPL-2.0


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

            
            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.


            nofilenametruncate

            
            		The file system will return an error when filename exceeds

            
            		standard maximum filename length (30 characters).


            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.


              - W maps to w.


              - E maps to x.


              - D is ignored.


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


              - A is cleared 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 allow R for user, group and others.


              - w permission will allow W for user, group and others.


              - x permission of the user will allow E for plain files.


              - D will be allowed for user, group and others.


              - 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/<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

            
            "/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 <disk> is the device name).


            DO AT YOUR OWN RISK::


              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

            
            fs/affs/Changes.


            By default, filenames are truncated to 30 characters without warning.

            
            'nofilenametruncate' mount option can change that behavior.


            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://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/
	.. SPDX-License-Identifier: GPL-2.0

	=============================
	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.

	nofilenametruncate
	The file system will return an error when filename exceeds
	standard maximum filename length (30 characters).

	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.

	- W maps to w.

	- E maps to x.

	- D is ignored.

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

	- A is cleared 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 allow R for user, group and others.

	- w permission will allow W for user, group and others.

	- x permission of the user will allow E for plain files.

	- D will be allowed for user, group and others.

	- 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/<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
	"/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 <disk> is the device name).

	DO AT YOUR OWN RISK::

	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
	fs/affs/Changes.

	By default, filenames are truncated to 30 characters without warning.
	'nofilenametruncate' mount option can change that behavior.

	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://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/