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 - If both W and D are allowed, w will be set. 114 115 - E maps to x. 116 117 - H and P are always retained and ignored under Linux. 118 119 - A is always reset when a file is written to. 120 121User id and group id will be used unless set[gu]id are given as mount 122options. Since most of the Amiga file systems are single user systems 123they will be owned by root. The root directory (the mount point) of the 124Amiga filesystem will be owned by the user who actually mounts the 125filesystem (the root directory doesn't have uid/gid fields). 126 127Linux -> Amiga: 128 129The Linux rwxrwxrwx file mode is handled as follows: 130 131 - r permission will set R for user, group and others. 132 133 - w permission will set W and D for user, group and others. 134 135 - x permission of the user will set E for plain files. 136 137 - All other flags (suid, sgid, ...) are ignored and will 138 not be retained. 139 140Newly created files and directories will get the user and group ID 141of the current user and a mode according to the umask. 142 143Symbolic links 144============== 145 146Although the Amiga and Linux file systems resemble each other, there 147are some, not always subtle, differences. One of them becomes apparent 148with symbolic links. While Linux has a file system with exactly one 149root directory, the Amiga has a separate root directory for each 150file system (for example, partition, floppy disk, ...). With the Amiga, 151these entities are called "volumes". They have symbolic names which 152can be used to access them. Thus, symbolic links can point to a 153different volume. AFFS turns the volume name into a directory name 154and prepends the prefix path (see prefix option) to it. 155 156Example: 157You mount all your Amiga partitions under /amiga/<volume> (where 158<volume> is the name of the volume), and you give the option 159"prefix=/amiga/" when mounting all your AFFS partitions. (They 160might be "User", "WB" and "Graphics", the mount points /amiga/User, 161/amiga/WB and /amiga/Graphics). A symbolic link referring to 162"User:sc/include/dos/dos.h" will be followed to 163"/amiga/User/sc/include/dos/dos.h". 164 165Examples 166======== 167 168Command line:: 169 170 mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose 171 mount /dev/sda3 /Amiga -t affs 172 173/etc/fstab entry:: 174 175 /dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0 176 177IMPORTANT NOTE 178============== 179 180If you boot Windows 95 (don't know about 3.x, 98 and NT) while you 181have an Amiga harddisk connected to your PC, it will overwrite 182the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating 183the Rigid Disk Block. Sheer luck has it that this is an unused 184area of the RDB, so only the checksum doesn't match anymore. 185Linux will ignore this garbage and recognize the RDB anyway, but 186before you connect that drive to your Amiga again, you must 187restore or repair your RDB. So please do make a backup copy of it 188before booting Windows! 189 190If the damage is already done, the following should fix the RDB 191(where <disk> is the device name). 192 193DO AT YOUR OWN RISK:: 194 195 dd if=/dev/<disk> of=rdb.tmp count=1 196 cp rdb.tmp rdb.fixed 197 dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4 198 dd if=rdb.fixed of=/dev/<disk> 199 200Bugs, Restrictions, Caveats 201=========================== 202 203Quite a few things may not work as advertised. Not everything is 204tested, though several hundred MB have been read and written using 205this fs. For a most up-to-date list of bugs please consult 206fs/affs/Changes. 207 208By default, filenames are truncated to 30 characters without warning. 209'nofilenametruncate' mount option can change that behavior. 210 211Case is ignored by the affs in filename matching, but Linux shells 212do care about the case. Example (with /wb being an affs mounted fs):: 213 214 rm /wb/WRONGCASE 215 216will remove /mnt/wrongcase, but:: 217 218 rm /wb/WR* 219 220will not since the names are matched by the shell. 221 222The block allocation is designed for hard disk partitions. If more 223than 1 process writes to a (small) diskette, the blocks are allocated 224in an ugly way (but the real AFFS doesn't do much better). This 225is also true when space gets tight. 226 227You cannot execute programs on an OFS (Old File System), since the 228program files cannot be memory mapped due to the 488 byte blocks. 229For the same reason you cannot mount an image on such a filesystem 230via the loopback device. 231 232The bitmap valid flag in the root block may not be accurate when the 233system crashes while an affs partition is mounted. There's currently 234no way to fix a garbled filesystem without an Amiga (disk validator) 235or manually (who would do this?). Maybe later. 236 237If you mount affs partitions on system startup, you may want to tell 238fsck that the fs should not be checked (place a '0' in the sixth field 239of /etc/fstab). 240 241It's not possible to read floppy disks with a normal PC or workstation 242due to an incompatibility with the Amiga floppy controller. 243 244If you are interested in an Amiga Emulator for Linux, look at 245 246http://web.archive.org/web/%2E/http://www.freiburg.linux.de/~uae/ 247