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Linus Torvalds1da177e2005-04-16 15:20:36 -07001Overview of Amiga Filesystems
2=============================
3
4Not all varieties of the Amiga filesystems are supported for reading and
5writing. The Amiga currently knows six different filesystems:
6
7DOS\0 The old or original filesystem, not really suited for
8 hard disks and normally not used on them, either.
9 Supported read/write.
10
11DOS\1 The original Fast File System. Supported read/write.
12
13DOS\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.
17
18DOS\3 The "international" Fast File System. Supported read/write.
19
20DOS\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.
24
25DOS\5 The Fast File System with directory cache. Supported read only.
26
27All of the above filesystems allow block sizes from 512 to 32K bytes.
28Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks
29speed up almost everything at the expense of wasted disk space. The speed
30gain above 4K seems not really worth the price, so you don't lose too
31much here, either.
32
33The muFS (multi user File System) equivalents of the above file systems
34are supported, too.
35
36Mount options for the AFFS
37==========================
38
39protect If this option is set, the protection bits cannot be altered.
40
41setuid[=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.
43
44setgid[=gid] Same as above, but for gid.
45
46mode=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.
51
52reserved=num Sets the number of reserved blocks at the start of the
53 partition to num. You should never need this option.
54 Default is 2.
55
56root=block Sets the block number of the root block. This should never
57 be necessary.
58
59bs=blksize Sets the blocksize to blksize. Valid block sizes are 512,
60 1024, 2048 and 4096. Like the root option, this should
61 never be necessary, as the affs can figure it out itself.
62
63quiet The file system will not return an error for disallowed
64 mode changes.
65
66verbose The volume name, file system type and block size will
67 be written to the syslog when the filesystem is mounted.
68
69mufs The filesystem is really a muFS, also it doesn't
70 identify itself as one. This option is necessary if
71 the filesystem wasn't formatted as muFS, but is used
72 as one.
73
74prefix=path Path will be prefixed to every absolute path name of
75 symbolic links on an AFFS partition. Default = "/".
76 (See below.)
77
78volume=name When symbolic links with an absolute path are created
79 on an AFFS partition, name will be prepended as the
80 volume name. Default = "" (empty string).
81 (See below.)
82
83Handling of the Users/Groups and protection flags
84=================================================
85
86Amiga -> Linux:
87
88The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
89
90 - R maps to r for user, group and others. On directories, R implies x.
91
92 - If both W and D are allowed, w will be set.
93
94 - E maps to x.
95
96 - H and P are always retained and ignored under Linux.
97
98 - A is always reset when a file is written to.
99
100User id and group id will be used unless set[gu]id are given as mount
101options. Since most of the Amiga file systems are single user systems
102they will be owned by root. The root directory (the mount point) of the
103Amiga filesystem will be owned by the user who actually mounts the
104filesystem (the root directory doesn't have uid/gid fields).
105
106Linux -> Amiga:
107
108The Linux rwxrwxrwx file mode is handled as follows:
109
110 - r permission will set R for user, group and others.
111
112 - w permission will set W and D for user, group and others.
113
114 - x permission of the user will set E for plain files.
115
116 - All other flags (suid, sgid, ...) are ignored and will
117 not be retained.
118
119Newly created files and directories will get the user and group ID
120of the current user and a mode according to the umask.
121
122Symbolic links
123==============
124
125Although the Amiga and Linux file systems resemble each other, there
126are some, not always subtle, differences. One of them becomes apparent
127with symbolic links. While Linux has a file system with exactly one
128root directory, the Amiga has a separate root directory for each
129file system (for example, partition, floppy disk, ...). With the Amiga,
130these entities are called "volumes". They have symbolic names which
131can be used to access them. Thus, symbolic links can point to a
132different volume. AFFS turns the volume name into a directory name
133and prepends the prefix path (see prefix option) to it.
134
135Example:
136You mount all your Amiga partitions under /amiga/<volume> (where
137<volume> is the name of the volume), and you give the option
138"prefix=/amiga/" when mounting all your AFFS partitions. (They
139might be "User", "WB" and "Graphics", the mount points /amiga/User,
140/amiga/WB and /amiga/Graphics). A symbolic link referring to
141"User:sc/include/dos/dos.h" will be followed to
142"/amiga/User/sc/include/dos/dos.h".
143
144Examples
145========
146
147Command line:
148 mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
149 mount /dev/sda3 /Amiga -t affs
150
151/etc/fstab entry:
152 /dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0
153
154IMPORTANT NOTE
155==============
156
157If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
158have an Amiga harddisk connected to your PC, it will overwrite
159the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
160the Rigid Disk Block. Sheer luck has it that this is an unused
161area of the RDB, so only the checksum doesn't match anymore.
162Linux will ignore this garbage and recognize the RDB anyway, but
163before you connect that drive to your Amiga again, you must
164restore or repair your RDB. So please do make a backup copy of it
165before booting Windows!
166
167If the damage is already done, the following should fix the RDB
168(where <disk> is the device name).
169DO AT YOUR OWN RISK:
170
171 dd if=/dev/<disk> of=rdb.tmp count=1
172 cp rdb.tmp rdb.fixed
173 dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4
174 dd if=rdb.fixed of=/dev/<disk>
175
176Bugs, Restrictions, Caveats
177===========================
178
179Quite a few things may not work as advertised. Not everything is
180tested, though several hundred MB have been read and written using
181this fs. For a most up-to-date list of bugs please consult
182fs/affs/Changes.
183
184Filenames are truncated to 30 characters without warning (this
185can be changed by setting the compile-time option AFFS_NO_TRUNCATE
186in include/linux/amigaffs.h).
187
188Case is ignored by the affs in filename matching, but Linux shells
189do care about the case. Example (with /wb being an affs mounted fs):
190 rm /wb/WRONGCASE
191will remove /mnt/wrongcase, but
192 rm /wb/WR*
193will not since the names are matched by the shell.
194
195The block allocation is designed for hard disk partitions. If more
196than 1 process writes to a (small) diskette, the blocks are allocated
197in an ugly way (but the real AFFS doesn't do much better). This
198is also true when space gets tight.
199
200You cannot execute programs on an OFS (Old File System), since the
201program files cannot be memory mapped due to the 488 byte blocks.
202For the same reason you cannot mount an image on such a filesystem
203via the loopback device.
204
205The bitmap valid flag in the root block may not be accurate when the
206system crashes while an affs partition is mounted. There's currently
207no way to fix a garbled filesystem without an Amiga (disk validator)
208or manually (who would do this?). Maybe later.
209
210If you mount affs partitions on system startup, you may want to tell
211fsck that the fs should not be checked (place a '0' in the sixth field
212of /etc/fstab).
213
214It's not possible to read floppy disks with a normal PC or workstation
215due to an incompatibility with the Amiga floppy controller.
216
217If you are interested in an Amiga Emulator for Linux, look at
218
219http://www-users.informatik.rwth-aachen.de/~crux/uae.html