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1da177e4 LT |
1 | Overview of Amiga Filesystems |
2 | ============================= | |
3 | ||
4 | Not all varieties of the Amiga filesystems are supported for reading and | |
5 | writing. The Amiga currently knows six different filesystems: | |
6 | ||
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. | |
10 | ||
11 | DOS\1 The original Fast File System. Supported read/write. | |
12 | ||
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. | |
17 | ||
18 | DOS\3 The "international" Fast File System. Supported read/write. | |
19 | ||
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. | |
24 | ||
25 | DOS\5 The Fast File System with directory cache. Supported read only. | |
26 | ||
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. | |
32 | ||
33 | The muFS (multi user File System) equivalents of the above file systems | |
34 | are supported, too. | |
35 | ||
36 | Mount options for the AFFS | |
37 | ========================== | |
38 | ||
39 | protect If this option is set, the protection bits cannot be altered. | |
40 | ||
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. | |
43 | ||
44 | setgid[=gid] Same as above, but for gid. | |
45 | ||
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. | |
51 | ||
52 | reserved=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 | ||
56 | root=block Sets the block number of the root block. This should never | |
57 | be necessary. | |
58 | ||
59 | bs=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 | ||
63 | quiet The file system will not return an error for disallowed | |
64 | mode changes. | |
65 | ||
66 | verbose The volume name, file system type and block size will | |
67 | be written to the syslog when the filesystem is mounted. | |
68 | ||
69 | mufs 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 | ||
74 | prefix=path Path will be prefixed to every absolute path name of | |
75 | symbolic links on an AFFS partition. Default = "/". | |
76 | (See below.) | |
77 | ||
78 | volume=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 | ||
83 | Handling of the Users/Groups and protection flags | |
84 | ================================================= | |
85 | ||
86 | Amiga -> Linux: | |
87 | ||
88 | The 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 | ||
100 | User id and group id will be used unless set[gu]id are given as mount | |
101 | options. Since most of the Amiga file systems are single user systems | |
102 | they will be owned by root. The root directory (the mount point) of the | |
103 | Amiga filesystem will be owned by the user who actually mounts the | |
104 | filesystem (the root directory doesn't have uid/gid fields). | |
105 | ||
106 | Linux -> Amiga: | |
107 | ||
108 | The 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 | ||
119 | Newly created files and directories will get the user and group ID | |
120 | of the current user and a mode according to the umask. | |
121 | ||
122 | Symbolic links | |
123 | ============== | |
124 | ||
125 | Although the Amiga and Linux file systems resemble each other, there | |
126 | are some, not always subtle, differences. One of them becomes apparent | |
127 | with symbolic links. While Linux has a file system with exactly one | |
128 | root directory, the Amiga has a separate root directory for each | |
129 | file system (for example, partition, floppy disk, ...). With the Amiga, | |
130 | these entities are called "volumes". They have symbolic names which | |
131 | can be used to access them. Thus, symbolic links can point to a | |
132 | different volume. AFFS turns the volume name into a directory name | |
133 | and prepends the prefix path (see prefix option) to it. | |
134 | ||
135 | Example: | |
136 | You 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 | |
139 | might 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 | ||
144 | Examples | |
145 | ======== | |
146 | ||
147 | Command 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 | ||
154 | IMPORTANT NOTE | |
155 | ============== | |
156 | ||
157 | If you boot Windows 95 (don't know about 3.x, 98 and NT) while you | |
158 | have an Amiga harddisk connected to your PC, it will overwrite | |
159 | the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating | |
160 | the Rigid Disk Block. Sheer luck has it that this is an unused | |
161 | area of the RDB, so only the checksum doesn't match anymore. | |
162 | Linux will ignore this garbage and recognize the RDB anyway, but | |
163 | before you connect that drive to your Amiga again, you must | |
164 | restore or repair your RDB. So please do make a backup copy of it | |
165 | before booting Windows! | |
166 | ||
167 | If the damage is already done, the following should fix the RDB | |
168 | (where <disk> is the device name). | |
169 | DO 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 | ||
176 | Bugs, Restrictions, Caveats | |
177 | =========================== | |
178 | ||
179 | Quite a few things may not work as advertised. Not everything is | |
180 | tested, though several hundred MB have been read and written using | |
181 | this fs. For a most up-to-date list of bugs please consult | |
182 | fs/affs/Changes. | |
183 | ||
184 | Filenames are truncated to 30 characters without warning (this | |
185 | can be changed by setting the compile-time option AFFS_NO_TRUNCATE | |
186 | in include/linux/amigaffs.h). | |
187 | ||
188 | Case is ignored by the affs in filename matching, but Linux shells | |
189 | do care about the case. Example (with /wb being an affs mounted fs): | |
190 | rm /wb/WRONGCASE | |
191 | will remove /mnt/wrongcase, but | |
192 | rm /wb/WR* | |
193 | will not since the names are matched by the shell. | |
194 | ||
195 | The block allocation is designed for hard disk partitions. If more | |
196 | than 1 process writes to a (small) diskette, the blocks are allocated | |
197 | in an ugly way (but the real AFFS doesn't do much better). This | |
198 | is also true when space gets tight. | |
199 | ||
200 | You cannot execute programs on an OFS (Old File System), since the | |
201 | program files cannot be memory mapped due to the 488 byte blocks. | |
202 | For the same reason you cannot mount an image on such a filesystem | |
203 | via the loopback device. | |
204 | ||
205 | The bitmap valid flag in the root block may not be accurate when the | |
206 | system crashes while an affs partition is mounted. There's currently | |
207 | no way to fix a garbled filesystem without an Amiga (disk validator) | |
208 | or manually (who would do this?). Maybe later. | |
209 | ||
210 | If you mount affs partitions on system startup, you may want to tell | |
211 | fsck that the fs should not be checked (place a '0' in the sixth field | |
212 | of /etc/fstab). | |
213 | ||
214 | It's not possible to read floppy disks with a normal PC or workstation | |
215 | due to an incompatibility with the Amiga floppy controller. | |
216 | ||
217 | If you are interested in an Amiga Emulator for Linux, look at | |
218 | ||
219 | http://www-users.informatik.rwth-aachen.de/~crux/uae.html |