Documentation/filesystems/affs.rst - third_party/kernel - 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/