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added man page for pcfs, the MS-DOS filesystem

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cgd 1993-04-09 20:24:59 +00:00
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commit e5b9395979
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share/man/man5/Makefile
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# @(#)Makefile 5.7.1.1 (Berkeley) 5/7/91
MAN5= a.out.0 acct.0 core.0 dir.0 disktab.0 fs.0 fstab.0 \
group.0 hosts.0 networks.0 passwd.0 phones.0 printcap.0 \
group.0 hosts.0 networks.0 passwd.0 pcfs.0 phones.0 printcap.0 \
protocols.0 remote.0 resolver.0 services.0 shells.0 stab.0 types.0 \
utmp.0
MLINKS= fs.5 inode.5 utmp.5 wtmp.5

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share/man/man5/pcfs.5 Normal file
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PCFS quirks file
PCFS filesystems on floppy disks only are supported in this release.
And, only high density floppy disks are supported. This is because
the floppy disk driver only supports high density disks.
Created files use only the user permissions bits. And of these
only the write bit is meaningful. DOS files always have the
execute and read bits on.
PCFS does not turn on or off the DOS archive attribute bit.
The timestamp on dos files is updated when ever the file is modified.
There is no inode time or create time stamp.
The timestamp placed on a dos file does not have corrections for
daylight savings time included. It does have the correction for
timezone though.
Unix times before 1980 will have their year set to 1980 in dos file
timestamps. This is because dos's idea of time starts in 1980.
PCFS filesystems do not support sparse files. Any attempt to seek
past the end of a file results in the blocks being allocated and
cleared.
When read() is used to examine pcfs directories you will get dos
directory contents. Note that the root directory does not contain
a "." or ".." entry. Only the readdir() system call simulates these
entries in the root directory of a dos filesystem. readdir() returns
directory entries as described in getdirentries(2).
Using read() and write() to manipulate the contents of dos directories
is unwise on an active dos filesystem since a more up to date copy of
their contents may reside in data structures in the kernel. It is
probably safe to examine the filename field of dos directory entries.
The filesystem code keeps this up to date at all times.
The cluster allocation algorithm is very simplistic. It starts at
cluster 2 and searchs until the last cluster of the filesystem and
takes the first available cluster.
The fsync() system call does not work on file descriptors open on
directories. This isn't a terrible thing since very few programs
open directories for writing.
The pcfs filesystem truncates filenames quietly. If a filename has
more than 8 characters before the 1st period only the 1st eigth are
used. It only uses the 1st three characters after the period if
they exist. The filenames "abc" and "abc." are the same to pcfs.
Filenames that begin with a "." are considered to be dos filenames
with an extension only and so are limited to 3 characters after the
leading ".". For example ".imlost" would be seen as ".iml" by pcfs.
PCFS folds filenames to upper case before writing them to disk or
looking up filenames, and folds them to lower case when reading them
from disk for presentation to the user (for example by readdir()).
Directory entries for the DOS filesystem label are quietly ignored.
This is probably going to be a problem. This implementation expects
the length of the root directory to be a multiple of the size of
a cluster. If this is not true a warning message is printed when
the filesystem is mounted.
PCFS supports DOS filesystems with 12 bit or 16 bit FATs. It supports
both regular and huge filesystems ( > 32 megabytes). It supports
both version 3.3 and 5.0 BPB's. Don't know about version 4.x and
less than 3.3. It has not been tested with 16 bit fats or huge
filesystems. This is because the hard disk drivers need to support
dos partitions to do these things.
PCFS does not support symbolic links or hard links. It does not
support quotas. How could it, pcfs files have no owners. PCFS
files have a simulated owner and group of 0. PCFS does not support
file locking. Though it may in the future. PCFS filesystems are
not remote mountable, but they will be in the future.
This is the first release and as such has performance problems.
Reading large files is very slow because the read ahead code in pcfs_read()
doesn't read far enough ahead for filesystems with small blocksizes.
Performance and dos hard disk paritions are the next areas to be
worked on. Unless someone else does it.
Operational Details
-------------------
To mount a pcfs filesystem:
mount -t pcfs /dev/fd0a /mnt
To unmount a pcfs filesystem:
umount /mnt
If you want to be sure the fat is ALWAYS up to date, mount the
filesystem with the synchronous option:
mount -t pcfs -o synchronous /dev/fd0a /mnt
This reasults in very slow file write performance because it turns
off write behind of fst disk blocks.
Configuring PCFS into your kernel
---------------------------------
Add the following statements to your configuration file in /sys/i386/conf/BLOT.
Or whatever you call your config file.
options PCFS
PCFS consumes approximately 24000 bytes of kernel code space and
approximately 4000 bytes of bss.
PCFS has some debug printf's that can be turned on by defining PCFSDEBUG.
It produces lots of output. If you use it be sure to kill syslogd before
using a PCFS filesystem with debug.