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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
Fabian Frederick8ca57722014-04-07 15:39:01 -070052nofilenametruncate
53 The file system will return an error when filename exceeds
54 standard maximum filename length (30 characters).
55
Linus Torvalds1da177e2005-04-16 15:20:36 -070056reserved=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.
59
60root=block Sets the block number of the root block. This should never
61 be necessary.
62
63bs=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.
66
67quiet The file system will not return an error for disallowed
68 mode changes.
69
70verbose The volume name, file system type and block size will
71 be written to the syslog when the filesystem is mounted.
72
73mufs 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.
77
78prefix=path Path will be prefixed to every absolute path name of
79 symbolic links on an AFFS partition. Default = "/".
80 (See below.)
81
82volume=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.)
86
87Handling of the Users/Groups and protection flags
88=================================================
89
90Amiga -> Linux:
91
92The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
93
94 - R maps to r for user, group and others. On directories, R implies x.
95
96 - If both W and D are allowed, w will be set.
97
98 - E maps to x.
99
100 - H and P are always retained and ignored under Linux.
101
102 - A is always reset when a file is written to.
103
104User id and group id will be used unless set[gu]id are given as mount
105options. Since most of the Amiga file systems are single user systems
106they will be owned by root. The root directory (the mount point) of the
107Amiga filesystem will be owned by the user who actually mounts the
108filesystem (the root directory doesn't have uid/gid fields).
109
110Linux -> Amiga:
111
112The Linux rwxrwxrwx file mode is handled as follows:
113
114 - r permission will set R for user, group and others.
115
116 - w permission will set W and D for user, group and others.
117
118 - x permission of the user will set E for plain files.
119
120 - All other flags (suid, sgid, ...) are ignored and will
121 not be retained.
122
123Newly created files and directories will get the user and group ID
124of the current user and a mode according to the umask.
125
126Symbolic links
127==============
128
129Although the Amiga and Linux file systems resemble each other, there
130are some, not always subtle, differences. One of them becomes apparent
131with symbolic links. While Linux has a file system with exactly one
132root directory, the Amiga has a separate root directory for each
133file system (for example, partition, floppy disk, ...). With the Amiga,
134these entities are called "volumes". They have symbolic names which
135can be used to access them. Thus, symbolic links can point to a
136different volume. AFFS turns the volume name into a directory name
137and prepends the prefix path (see prefix option) to it.
138
139Example:
140You 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
143might 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".
147
148Examples
149========
150
151Command line:
152 mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
153 mount /dev/sda3 /Amiga -t affs
154
155/etc/fstab entry:
156 /dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0
157
158IMPORTANT NOTE
159==============
160
161If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
162have an Amiga harddisk connected to your PC, it will overwrite
163the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
164the Rigid Disk Block. Sheer luck has it that this is an unused
165area of the RDB, so only the checksum doesn't match anymore.
166Linux will ignore this garbage and recognize the RDB anyway, but
167before you connect that drive to your Amiga again, you must
168restore or repair your RDB. So please do make a backup copy of it
169before booting Windows!
170
171If the damage is already done, the following should fix the RDB
172(where <disk> is the device name).
173DO AT YOUR OWN RISK:
174
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>
179
180Bugs, Restrictions, Caveats
181===========================
182
183Quite a few things may not work as advertised. Not everything is
184tested, though several hundred MB have been read and written using
185this fs. For a most up-to-date list of bugs please consult
186fs/affs/Changes.
187
Fabian Frederick8ca57722014-04-07 15:39:01 -0700188By default, filenames are truncated to 30 characters without warning.
189'nofilenametruncate' mount option can change that behavior.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190
191Case is ignored by the affs in filename matching, but Linux shells
192do care about the case. Example (with /wb being an affs mounted fs):
193 rm /wb/WRONGCASE
194will remove /mnt/wrongcase, but
195 rm /wb/WR*
196will not since the names are matched by the shell.
197
198The block allocation is designed for hard disk partitions. If more
199than 1 process writes to a (small) diskette, the blocks are allocated
200in an ugly way (but the real AFFS doesn't do much better). This
201is also true when space gets tight.
202
203You cannot execute programs on an OFS (Old File System), since the
204program files cannot be memory mapped due to the 488 byte blocks.
205For the same reason you cannot mount an image on such a filesystem
206via the loopback device.
207
208The bitmap valid flag in the root block may not be accurate when the
209system crashes while an affs partition is mounted. There's currently
210no way to fix a garbled filesystem without an Amiga (disk validator)
211or manually (who would do this?). Maybe later.
212
213If you mount affs partitions on system startup, you may want to tell
214fsck that the fs should not be checked (place a '0' in the sixth field
215of /etc/fstab).
216
217It's not possible to read floppy disks with a normal PC or workstation
218due to an incompatibility with the Amiga floppy controller.
219
220If you are interested in an Amiga Emulator for Linux, look at
221
Justin P. Mattock0ea6e612010-07-23 20:51:24 -0700222http://web.archive.org/web/*/http://www.freiburg.linux.de/~uae/