[mirror_ubuntu-hirsute-kernel.git] / Documentation / filesystems / affs.rst

.. 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/
Commit	Line	Data
76272168 MCC	1	.. SPDX-License-Identifier: GPL-2.0
	2
	3	=============================
1da177e4 LT	4	Overview of Amiga Filesystems
	5	=============================
	6
	7	Not all varieties of the Amiga filesystems are supported for reading and
	8	writing. The Amiga currently knows six different filesystems:
	9
76272168	10	============== ===============================================================
1da177e4 LT	11	DOS\0 The old or original filesystem, not really suited for
	12	hard disks and normally not used on them, either.
	13	Supported read/write.
	14
	15	DOS\1 The original Fast File System. Supported read/write.
	16
	17	DOS\2 The old "international" filesystem. International means that
	18	a bug has been fixed so that accented ("international") letters
	19	in file names are case-insensitive, as they ought to be.
	20	Supported read/write.
	21
	22	DOS\3 The "international" Fast File System. Supported read/write.
	23
	24	DOS\4 The original filesystem with directory cache. The directory
	25	cache speeds up directory accesses on floppies considerably,
	26	but slows down file creation/deletion. Doesn't make much
	27	sense on hard disks. Supported read only.
	28
	29	DOS\5 The Fast File System with directory cache. Supported read only.
76272168	30	============== ===============================================================
1da177e4 LT	31
	32	All of the above filesystems allow block sizes from 512 to 32K bytes.
	33	Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks
	34	speed up almost everything at the expense of wasted disk space. The speed
	35	gain above 4K seems not really worth the price, so you don't lose too
	36	much here, either.
	37
	38	The muFS (multi user File System) equivalents of the above file systems
	39	are supported, too.
	40
	41	Mount options for the AFFS
	42	==========================
	43
76272168 MCC	44	protect
76272168 MCC	45	If this option is set, the protection bits cannot be altered.
1da177e4	46
76272168 MCC	47	setuid[=uid]
76272168 MCC	48	This sets the owner of all files and directories in the file
1da177e4 LT	49	system to uid or the uid of the current user, respectively.
1da177e4 LT	50
76272168 MCC	51	setgid[=gid]
76272168 MCC	52	Same as above, but for gid.
1da177e4	53
76272168 MCC	54	mode=mode
76272168 MCC	55	Sets the mode flags to the given (octal) value, regardless
1da177e4 LT	56	of the original permissions. Directories will get an x
	57	permission if the corresponding r bit is set.
	58	This is useful since most of the plain AmigaOS files
	59	will map to 600.
	60
8ca57722 FF	61	nofilenametruncate
	62	The file system will return an error when filename exceeds
	63	standard maximum filename length (30 characters).
	64
76272168 MCC	65	reserved=num
76272168 MCC	66	Sets the number of reserved blocks at the start of the
1da177e4 LT	67	partition to num. You should never need this option.
	68	Default is 2.
	69
76272168 MCC	70	root=block
76272168 MCC	71	Sets the block number of the root block. This should never
1da177e4 LT	72	be necessary.
1da177e4 LT	73
76272168 MCC	74	bs=blksize
76272168 MCC	75	Sets the blocksize to blksize. Valid block sizes are 512,
1da177e4 LT	76	1024, 2048 and 4096. Like the root option, this should
	77	never be necessary, as the affs can figure it out itself.
	78
76272168 MCC	79	quiet
76272168 MCC	80	The file system will not return an error for disallowed
1da177e4 LT	81	mode changes.
1da177e4 LT	82
76272168 MCC	83	verbose
76272168 MCC	84	The volume name, file system type and block size will
1da177e4 LT	85	be written to the syslog when the filesystem is mounted.
1da177e4 LT	86
76272168 MCC	87	mufs
76272168 MCC	88	The filesystem is really a muFS, also it doesn't
1da177e4 LT	89	identify itself as one. This option is necessary if
	90	the filesystem wasn't formatted as muFS, but is used
	91	as one.
	92
76272168 MCC	93	prefix=path
76272168 MCC	94	Path will be prefixed to every absolute path name of
1da177e4 LT	95	symbolic links on an AFFS partition. Default = "/".
	96	(See below.)
	97
76272168 MCC	98	volume=name
76272168 MCC	99	When symbolic links with an absolute path are created
1da177e4 LT	100	on an AFFS partition, name will be prepended as the
	101	volume name. Default = "" (empty string).
	102	(See below.)
	103
	104	Handling of the Users/Groups and protection flags
	105	=================================================
	106
	107	Amiga -> Linux:
	108
	109	The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
	110
	111	- R maps to r for user, group and others. On directories, R implies x.
	112
d3a84a8d	113	- W maps to w.
1da177e4 LT	114
	115	- E maps to x.
	116
d3a84a8d	117	- D is ignored.
1da177e4	118
d3a84a8d MS	119	- H, S and P are always retained and ignored under Linux.
	120
	121	- A is cleared when a file is written to.
1da177e4 LT	122
	123	User id and group id will be used unless set[gu]id are given as mount
	124	options. Since most of the Amiga file systems are single user systems
	125	they will be owned by root. The root directory (the mount point) of the
	126	Amiga filesystem will be owned by the user who actually mounts the
	127	filesystem (the root directory doesn't have uid/gid fields).
	128
	129	Linux -> Amiga:
	130
	131	The Linux rwxrwxrwx file mode is handled as follows:
	132
d3a84a8d MS	133	- r permission will allow R for user, group and others.
	134
	135	- w permission will allow W for user, group and others.
1da177e4	136
d3a84a8d	137	- x permission of the user will allow E for plain files.
1da177e4	138
d3a84a8d	139	- D will be allowed for user, group and others.
1da177e4 LT	140
	141	- All other flags (suid, sgid, ...) are ignored and will
	142	not be retained.
76272168	143
1da177e4 LT	144	Newly created files and directories will get the user and group ID
	145	of the current user and a mode according to the umask.
	146
	147	Symbolic links
	148	==============
	149
	150	Although the Amiga and Linux file systems resemble each other, there
	151	are some, not always subtle, differences. One of them becomes apparent
	152	with symbolic links. While Linux has a file system with exactly one
	153	root directory, the Amiga has a separate root directory for each
	154	file system (for example, partition, floppy disk, ...). With the Amiga,
	155	these entities are called "volumes". They have symbolic names which
	156	can be used to access them. Thus, symbolic links can point to a
	157	different volume. AFFS turns the volume name into a directory name
	158	and prepends the prefix path (see prefix option) to it.
	159
	160	Example:
	161	You mount all your Amiga partitions under /amiga/<volume> (where
	162	<volume> is the name of the volume), and you give the option
	163	"prefix=/amiga/" when mounting all your AFFS partitions. (They
	164	might be "User", "WB" and "Graphics", the mount points /amiga/User,
	165	/amiga/WB and /amiga/Graphics). A symbolic link referring to
	166	"User:sc/include/dos/dos.h" will be followed to
	167	"/amiga/User/sc/include/dos/dos.h".
	168
	169	Examples
	170	========
	171
76272168 MCC	172	Command line::
76272168 MCC	173
1da177e4 LT	174	mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
	175	mount /dev/sda3 /Amiga -t affs
	176
76272168 MCC	177	/etc/fstab entry::
76272168 MCC	178
1da177e4 LT	179	/dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0
	180
	181	IMPORTANT NOTE
	182	==============
	183
	184	If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
	185	have an Amiga harddisk connected to your PC, it will overwrite
	186	the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
	187	the Rigid Disk Block. Sheer luck has it that this is an unused
	188	area of the RDB, so only the checksum doesn't match anymore.
	189	Linux will ignore this garbage and recognize the RDB anyway, but
	190	before you connect that drive to your Amiga again, you must
	191	restore or repair your RDB. So please do make a backup copy of it
	192	before booting Windows!
	193
	194	If the damage is already done, the following should fix the RDB
	195	(where <disk> is the device name).
76272168 MCC	196
76272168 MCC	197	DO AT YOUR OWN RISK::
1da177e4 LT	198
	199	dd if=/dev/<disk> of=rdb.tmp count=1
	200	cp rdb.tmp rdb.fixed
	201	dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4
	202	dd if=rdb.fixed of=/dev/<disk>
	203
	204	Bugs, Restrictions, Caveats
	205	===========================
	206
	207	Quite a few things may not work as advertised. Not everything is
	208	tested, though several hundred MB have been read and written using
	209	this fs. For a most up-to-date list of bugs please consult
	210	fs/affs/Changes.
	211
8ca57722 FF	212	By default, filenames are truncated to 30 characters without warning.
8ca57722 FF	213	'nofilenametruncate' mount option can change that behavior.
1da177e4 LT	214
1da177e4 LT	215	Case is ignored by the affs in filename matching, but Linux shells
76272168 MCC	216	do care about the case. Example (with /wb being an affs mounted fs)::
76272168 MCC	217
1da177e4	218	rm /wb/WRONGCASE
76272168 MCC	219
	220	will remove /mnt/wrongcase, but::
	221
1da177e4	222	rm /wb/WR*
76272168	223
1da177e4 LT	224	will not since the names are matched by the shell.
	225
	226	The block allocation is designed for hard disk partitions. If more
	227	than 1 process writes to a (small) diskette, the blocks are allocated
	228	in an ugly way (but the real AFFS doesn't do much better). This
	229	is also true when space gets tight.
	230
	231	You cannot execute programs on an OFS (Old File System), since the
	232	program files cannot be memory mapped due to the 488 byte blocks.
	233	For the same reason you cannot mount an image on such a filesystem
	234	via the loopback device.
	235
	236	The bitmap valid flag in the root block may not be accurate when the
	237	system crashes while an affs partition is mounted. There's currently
	238	no way to fix a garbled filesystem without an Amiga (disk validator)
	239	or manually (who would do this?). Maybe later.
	240
	241	If you mount affs partitions on system startup, you may want to tell
	242	fsck that the fs should not be checked (place a '0' in the sixth field
	243	of /etc/fstab).
	244
	245	It's not possible to read floppy disks with a normal PC or workstation
	246	due to an incompatibility with the Amiga floppy controller.
	247
	248	If you are interested in an Amiga Emulator for Linux, look at
	249
76272168	250	http://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/