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Documentation / filesystems / affs.txt

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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

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