220 lines
8.0 KiB
Plaintext
220 lines
8.0 KiB
Plaintext
Overview of Amiga Filesystems
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=============================
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Not all varieties of the Amiga filesystems are supported for reading and
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writing. The Amiga currently knows six different filesystems:
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DOS\0 The old or original filesystem, not really suited for
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hard disks and normally not used on them, either.
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Supported read/write.
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DOS\1 The original Fast File System. Supported read/write.
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DOS\2 The old "international" filesystem. International means that
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a bug has been fixed so that accented ("international") letters
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in file names are case-insensitive, as they ought to be.
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Supported read/write.
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DOS\3 The "international" Fast File System. Supported read/write.
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DOS\4 The original filesystem with directory cache. The directory
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cache speeds up directory accesses on floppies considerably,
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but slows down file creation/deletion. Doesn't make much
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sense on hard disks. Supported read only.
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DOS\5 The Fast File System with directory cache. Supported read only.
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All of the above filesystems allow block sizes from 512 to 32K bytes.
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Supported block sizes are: 512, 1024, 2048 and 4096 bytes. Larger blocks
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speed up almost everything at the expense of wasted disk space. The speed
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gain above 4K seems not really worth the price, so you don't lose too
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much here, either.
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The muFS (multi user File System) equivalents of the above file systems
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are supported, too.
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Mount options for the AFFS
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==========================
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protect If this option is set, the protection bits cannot be altered.
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setuid[=uid] This sets the owner of all files and directories in the file
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system to uid or the uid of the current user, respectively.
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setgid[=gid] Same as above, but for gid.
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mode=mode Sets the mode flags to the given (octal) value, regardless
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of the original permissions. Directories will get an x
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permission if the corresponding r bit is set.
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This is useful since most of the plain AmigaOS files
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will map to 600.
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reserved=num Sets the number of reserved blocks at the start of the
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partition to num. You should never need this option.
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Default is 2.
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root=block Sets the block number of the root block. This should never
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be necessary.
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bs=blksize Sets the blocksize to blksize. Valid block sizes are 512,
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1024, 2048 and 4096. Like the root option, this should
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never be necessary, as the affs can figure it out itself.
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quiet The file system will not return an error for disallowed
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mode changes.
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verbose The volume name, file system type and block size will
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be written to the syslog when the filesystem is mounted.
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mufs The filesystem is really a muFS, also it doesn't
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identify itself as one. This option is necessary if
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the filesystem wasn't formatted as muFS, but is used
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as one.
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prefix=path Path will be prefixed to every absolute path name of
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symbolic links on an AFFS partition. Default = "/".
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(See below.)
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volume=name When symbolic links with an absolute path are created
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on an AFFS partition, name will be prepended as the
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volume name. Default = "" (empty string).
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(See below.)
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Handling of the Users/Groups and protection flags
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=================================================
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Amiga -> Linux:
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The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
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- R maps to r for user, group and others. On directories, R implies x.
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- If both W and D are allowed, w will be set.
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- E maps to x.
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- H and P are always retained and ignored under Linux.
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- A is always reset when a file is written to.
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User id and group id will be used unless set[gu]id are given as mount
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options. Since most of the Amiga file systems are single user systems
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they will be owned by root. The root directory (the mount point) of the
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Amiga filesystem will be owned by the user who actually mounts the
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filesystem (the root directory doesn't have uid/gid fields).
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Linux -> Amiga:
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The Linux rwxrwxrwx file mode is handled as follows:
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- r permission will set R for user, group and others.
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- w permission will set W and D for user, group and others.
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- x permission of the user will set E for plain files.
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- All other flags (suid, sgid, ...) are ignored and will
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not be retained.
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Newly created files and directories will get the user and group ID
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of the current user and a mode according to the umask.
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Symbolic links
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==============
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Although the Amiga and Linux file systems resemble each other, there
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are some, not always subtle, differences. One of them becomes apparent
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with symbolic links. While Linux has a file system with exactly one
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root directory, the Amiga has a separate root directory for each
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file system (for example, partition, floppy disk, ...). With the Amiga,
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these entities are called "volumes". They have symbolic names which
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can be used to access them. Thus, symbolic links can point to a
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different volume. AFFS turns the volume name into a directory name
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and prepends the prefix path (see prefix option) to it.
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Example:
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You mount all your Amiga partitions under /amiga/<volume> (where
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<volume> is the name of the volume), and you give the option
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"prefix=/amiga/" when mounting all your AFFS partitions. (They
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might be "User", "WB" and "Graphics", the mount points /amiga/User,
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/amiga/WB and /amiga/Graphics). A symbolic link referring to
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"User:sc/include/dos/dos.h" will be followed to
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"/amiga/User/sc/include/dos/dos.h".
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Examples
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========
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Command line:
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mount Archive/Amiga/Workbench3.1.adf /mnt -t affs -o loop,verbose
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mount /dev/sda3 /Amiga -t affs
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/etc/fstab entry:
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/dev/sdb5 /amiga/Workbench affs noauto,user,exec,verbose 0 0
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IMPORTANT NOTE
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==============
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If you boot Windows 95 (don't know about 3.x, 98 and NT) while you
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have an Amiga harddisk connected to your PC, it will overwrite
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the bytes 0x00dc..0x00df of block 0 with garbage, thus invalidating
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the Rigid Disk Block. Sheer luck has it that this is an unused
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area of the RDB, so only the checksum doesn't match anymore.
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Linux will ignore this garbage and recognize the RDB anyway, but
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before you connect that drive to your Amiga again, you must
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restore or repair your RDB. So please do make a backup copy of it
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before booting Windows!
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If the damage is already done, the following should fix the RDB
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(where <disk> is the device name).
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DO AT YOUR OWN RISK:
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dd if=/dev/<disk> of=rdb.tmp count=1
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cp rdb.tmp rdb.fixed
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dd if=/dev/zero of=rdb.fixed bs=1 seek=220 count=4
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dd if=rdb.fixed of=/dev/<disk>
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Bugs, Restrictions, Caveats
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===========================
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Quite a few things may not work as advertised. Not everything is
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tested, though several hundred MB have been read and written using
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this fs. For a most up-to-date list of bugs please consult
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fs/affs/Changes.
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Filenames are truncated to 30 characters without warning (this
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can be changed by setting the compile-time option AFFS_NO_TRUNCATE
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in include/linux/amigaffs.h).
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Case is ignored by the affs in filename matching, but Linux shells
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do care about the case. Example (with /wb being an affs mounted fs):
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rm /wb/WRONGCASE
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will remove /mnt/wrongcase, but
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rm /wb/WR*
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will not since the names are matched by the shell.
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The block allocation is designed for hard disk partitions. If more
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than 1 process writes to a (small) diskette, the blocks are allocated
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in an ugly way (but the real AFFS doesn't do much better). This
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is also true when space gets tight.
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You cannot execute programs on an OFS (Old File System), since the
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program files cannot be memory mapped due to the 488 byte blocks.
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For the same reason you cannot mount an image on such a filesystem
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via the loopback device.
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The bitmap valid flag in the root block may not be accurate when the
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system crashes while an affs partition is mounted. There's currently
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no way to fix a garbled filesystem without an Amiga (disk validator)
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or manually (who would do this?). Maybe later.
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If you mount affs partitions on system startup, you may want to tell
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fsck that the fs should not be checked (place a '0' in the sixth field
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of /etc/fstab).
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It's not possible to read floppy disks with a normal PC or workstation
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due to an incompatibility with the Amiga floppy controller.
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If you are interested in an Amiga Emulator for Linux, look at
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http://web.archive.org/web/*/http://www.freiburg.linux.de/~uae/
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