affs.rst (8613B)
1.. SPDX-License-Identifier: GPL-2.0 2 3============================= 4Overview of Amiga Filesystems 5============================= 6 7Not all varieties of the Amiga filesystems are supported for reading and 8writing. The Amiga currently knows six different filesystems: 9 10============== =============================================================== 11DOS\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 15DOS\1 The original Fast File System. Supported read/write. 16 17DOS\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 22DOS\3 The "international" Fast File System. Supported read/write. 23 24DOS\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 29DOS\5 The Fast File System with directory cache. Supported read only. 30============== =============================================================== 31 32All of the above filesystems allow block sizes from 512 to 32K bytes. 33Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks 34speed up almost everything at the expense of wasted disk space. The speed 35gain above 4K seems not really worth the price, so you don't lose too 36much here, either. 37 38The muFS (multi user File System) equivalents of the above file systems 39are supported, too. 40 41Mount options for the AFFS 42========================== 43 44protect 45 If this option is set, the protection bits cannot be altered. 46 47setuid[=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 51setgid[=gid] 52 Same as above, but for gid. 53 54mode=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 61nofilenametruncate 62 The file system will return an error when filename exceeds 63 standard maximum filename length (30 characters). 64 65reserved=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 70root=block 71 Sets the block number of the root block. This should never 72 be necessary. 73 74bs=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 79quiet 80 The file system will not return an error for disallowed 81 mode changes. 82 83verbose 84 The volume name, file system type and block size will 85 be written to the syslog when the filesystem is mounted. 86 87mufs 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 93prefix=path 94 Path will be prefixed to every absolute path name of 95 symbolic links on an AFFS partition. Default = "/". 96 (See below.) 97 98volume=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 104Handling of the Users/Groups and protection flags 105================================================= 106 107Amiga -> Linux: 108 109The 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 123User id and group id will be used unless set[gu]id are given as mount 124options. Since most of the Amiga file systems are single user systems 125they will be owned by root. The root directory (the mount point) of the 126Amiga filesystem will be owned by the user who actually mounts the 127filesystem (the root directory doesn't have uid/gid fields). 128 129Linux -> Amiga: 130 131The 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 144Newly created files and directories will get the user and group ID 145of the current user and a mode according to the umask. 146 147Symbolic links 148============== 149 150Although the Amiga and Linux file systems resemble each other, there 151are some, not always subtle, differences. One of them becomes apparent 152with symbolic links. While Linux has a file system with exactly one 153root directory, the Amiga has a separate root directory for each 154file system (for example, partition, floppy disk, ...). With the Amiga, 155these entities are called "volumes". They have symbolic names which 156can be used to access them. Thus, symbolic links can point to a 157different volume. AFFS turns the volume name into a directory name 158and prepends the prefix path (see prefix option) to it. 159 160Example: 161You 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 164might 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 169Examples 170======== 171 172Command 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 181IMPORTANT NOTE 182============== 183 184If you boot Windows 95 (don't know about 3.x, 98 and NT) while you 185have an Amiga harddisk connected to your PC, it will overwrite 186the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating 187the Rigid Disk Block. Sheer luck has it that this is an unused 188area of the RDB, so only the checksum doesn't match anymore. 189Linux will ignore this garbage and recognize the RDB anyway, but 190before you connect that drive to your Amiga again, you must 191restore or repair your RDB. So please do make a backup copy of it 192before booting Windows! 193 194If the damage is already done, the following should fix the RDB 195(where <disk> is the device name). 196 197DO 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 204Bugs, Restrictions, Caveats 205=========================== 206 207Quite a few things may not work as advertised. Not everything is 208tested, though several hundred MB have been read and written using 209this fs. For a most up-to-date list of bugs please consult 210fs/affs/Changes. 211 212By default, filenames are truncated to 30 characters without warning. 213'nofilenametruncate' mount option can change that behavior. 214 215Case is ignored by the affs in filename matching, but Linux shells 216do care about the case. Example (with /wb being an affs mounted fs):: 217 218 rm /wb/WRONGCASE 219 220will remove /mnt/wrongcase, but:: 221 222 rm /wb/WR* 223 224will not since the names are matched by the shell. 225 226The block allocation is designed for hard disk partitions. If more 227than 1 process writes to a (small) diskette, the blocks are allocated 228in an ugly way (but the real AFFS doesn't do much better). This 229is also true when space gets tight. 230 231You cannot execute programs on an OFS (Old File System), since the 232program files cannot be memory mapped due to the 488 byte blocks. 233For the same reason you cannot mount an image on such a filesystem 234via the loopback device. 235 236The bitmap valid flag in the root block may not be accurate when the 237system crashes while an affs partition is mounted. There's currently 238no way to fix a garbled filesystem without an Amiga (disk validator) 239or manually (who would do this?). Maybe later. 240 241If you mount affs partitions on system startup, you may want to tell 242fsck that the fs should not be checked (place a '0' in the sixth field 243of /etc/fstab). 244 245It's not possible to read floppy disks with a normal PC or workstation 246due to an incompatibility with the Amiga floppy controller. 247 248If you are interested in an Amiga Emulator for Linux, look at 249 250http://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/