1 .. SPDX-License-Identifier: GPL-2.0
2
3 =============================
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
10 ============== ===============================================================
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.
30 ============== ===============================================================
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
44 protect
45 If this option is set, the protection bits cannot be altered.
46
47 setuid[=uid]
48 This sets the owner of all files and directories in the file
49 system to uid or the uid of the current user, respectively.
50
51 setgid[=gid]
52 Same as above, but for gid.
53
54 mode=mode
55 Sets the mode flags to the given (octal) value, regardless
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
61 nofilenametruncate
62 The file system will return an error when filename exceeds
63 standard maximum filename length (30 characters).
64
65 reserved=num
66 Sets the number of reserved blocks at the start of the
67 partition to num. You should never need this option.
68 Default is 2.
69
70 root=block
71 Sets the block number of the root block. This should never
72 be necessary.
73
74 bs=blksize
75 Sets the blocksize to blksize. Valid block sizes are 512,
76 1024, 2048 and 4096. Like the root option, this should
77 never be necessary, as the affs can figure it out itself.
78
79 quiet
80 The file system will not return an error for disallowed
81 mode changes.
82
83 verbose
84 The volume name, file system type and block size will
85 be written to the syslog when the filesystem is mounted.
86
87 mufs
88 The filesystem is really a muFS, also it doesn't
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
93 prefix=path
94 Path will be prefixed to every absolute path name of
95 symbolic links on an AFFS partition. Default = "/".
96 (See below.)
97
98 volume=name
99 When symbolic links with an absolute path are created
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
113 - W maps to w.
114
115 - E maps to x.
116
117 - D is ignored.
118
119 - H, S and P are always retained and ignored under Linux.
120
121 - A is cleared when a file is written to.
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
133 - r permission will allow R for user, group and others.
134
135 - w permission will allow W for user, group and others.
136
137 - x permission of the user will allow E for plain files.
138
139 - D will be allowed for user, group and others.
140
141 - All other flags (suid, sgid, ...) are ignored and will
142 not be retained.
143
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
172 Command line::
173
174 mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
175 mount /dev/sda3 /Amiga -t affs
176
177 /etc/fstab entry::
178
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).
196
197 DO AT YOUR OWN RISK::
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
212 By default, filenames are truncated to 30 characters without warning.
213 'nofilenametruncate' mount option can change that behavior.
214
215 Case is ignored by the affs in filename matching, but Linux shells
216 do care about the case. Example (with /wb being an affs mounted fs)::
217
218 rm /wb/WRONGCASE
219
220 will remove /mnt/wrongcase, but::
221
222 rm /wb/WR*
223
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
250 http://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/
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