CWFS(4) CWFS(4)
NAME
cwfs, cwfs64, cwfs64x, fs64 - cached-worm file server, dump
SYNOPSIS
cwfs [ -csC ] [ -n service ] [ -a announce-string ] ... [ -m
device-map ] [ -f config-device ]
DESCRIPTION
Cwfs is a cached-worm file server that runs as a user-mode
program and can maintain file systems created by fs(4), the
original Plan 9 file server that had its own kernel and
operated a standalone system with disks and optical-disc
jukebox attached. Unlike fs(4), which could only accept 9P
connections over IL/IPv4 on Ethernets (or over Datakit and
Cyclones, long ago), cwfs accepts 9P connections over any
network medium and protocol that it can announce on, by
default TCP (over IPv4 or IPv6). Given suitable 9P clients,
one could even run 9P over aan(8) or tls(3).
The stock cwfs implements a 16K file system block size and
32-bit disk addresses, in order to be compatible with some
existing file systems, notably emelie's. These parameters
can be changed by recompilation.
Cwfs places its server 9P connection in /srv/name and its
command pipe in /srv/name.cmd, where name is the service
name.
Options are:
-f specify config-device other than the default
`/dev/sdC0/cwfs'.
-a announce on announce-string, can be specified multiple
times.
-C use a newer, faster, and incompatible cache-device lay-
out. To convert an old file system's cache to the new
layout, dump the file system, note the last superblock
number, halt cwfs, restart cwfs with -cC, recover the
file system, and start cwfs with -C thereafter.
-c enter the file server's configuration mode before
starting normal operation.
-n overrides the service name of the file server's config-
uration.
-s Post file descriptor zero in /srv/service and read and
write protocol messages on file descriptor one.
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CWFS(4) CWFS(4)
-m the file device-map contains a simple device name
(e.g., `w9') and a replacement per line. The device
name is in the usual filsys notation of fsconfig(8).
The replacement can be the name of an existing file
(which cwfs will not grow) or another such device name.
For example, the file
w0 /tmp/w0
h1 w2
would map accesses to device `w0' to existing file
`/tmp/w0' and accesses to device `h1' to device `w2',
if no file named `w2' exists.
The file server normally requires all users except `none' to
provide authentication tickets on each attach(5). This can
be disabled using the noauth configuration command (see
fsconfig(8)).
The group numbered 9999, normally called noworld, is special
on the file server. Any user belonging to that group has
attenuated access privileges. Specifically, when checking
such a user's access to files, the file's permission bits
are first ANDed with 0770 for normal files or 0771 for
directories. The effect is to deny world access permissions
to noworld users, except when walking directories.
The user none is always allowed to attach to emelie without
authentication but has minimal permissions.
Emelie maintains three file systems on a combination of
disks and write-once-read-many (WORM) magneto-optical disks.
other
is a simple disk-based file system not backed by worm.
main is a worm-based file system with a disk-based look-
aside cache. The disk cache holds modified worm blocks
to overcome the write-once property of the worm. The
cache also holds recently accessed non-modified blocks
to speed up the effective access time of the worm.
Occasionally (usually daily at 5AM) the modified blocks
in the disk cache are dumped. At this time, traffic to
the file system is halted and the modified blocks are
relabeled to the unwritten portion of the worm. After
the dump, the file system traffic is continued and the
relabeled blocks are copied to the worm by a background
process.
dump Each time the main file system is dumped, its root is
appended to a subdirectory of the dump file system.
Since the dump file system is not mirrored with a disk
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CWFS(4) CWFS(4)
cache, it is read-only. The name of the newly added
root is created from the date of the dump: /yyyy/mmdds.
Here yyyy is the full year, mm is the month number, dd
is the day number and s is a sequence number if more
than one dump is done in a day. For the first dump, s
is null. For the subsequent dumps s is 1, 2, 3, etc.
The root of the main file system that is frozen on the
first dump of March 1, 1992 will be named /1992/0301/
in the dump file system.
Changes from fs
fs(4)'s IP configuration is ignored and the underlying
system's is used.
Various other fs(4) commands have been omitted since they
(or equivalents) can now be executed directly on the under-
lying CPU server, notably date and passwd (see auth/wrkey).
Files can be used directly as wren devices by giving a file
name rooted at / or using double or single quotes. Such a
file name can be appended to the `w' device instead of spec-
ifying `target' and `lun' numbers.
fs(4)'s device names `h' for IDE disks and `m' for Marvell
SATA disks are not supported; use -m to map wren devices to
appropriate names under /dev/sd*.
The file server kernel seems to have scanned PCI buses in
reverse order from the other Plan 9 kernels, so systems with
multiple SCSI cards may find controller numbering reversed.
-m can be used to compensate for this if you don't want to
change filsys declarations.
The file server kernel's config field in NVRAM was over-
loaded in recent times to hold a secstore(1) key for the CPU
hostowner. Since cwfs runs on a CPU kernel, the location of
its configuration block must be supplied on the command
line.
Disk labels are now implemented for l devices. At the first
access of a side, cwfs will attempt to read the label and
verify that it has the correct side number and byte order;
if either is wrong, it will issue a warning. If the label
cannot be read, cwfs will attempt to write a new label.
The original file server reserved the rest of the machines
RAM for io buffers. Where cwfs running under the Plan 9 ker-
nel reserves a settable percentage of the remaining user
pages. The percentage is read from the environment variable
fsmempercent which when not set is assumed to be 25%
(default).
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EXAMPLES
Place the root of the dump file system on /n/dump and show
the modified times of the MIPS C compiler over all dumps in
February, 1992:
cwfs w0
9fs dump
ls -l /n/dump/1992/02??/mips/bin/vc
To get only one line of output for each version of the com-
piler:
ls -lp /n/dump/1992/02??/mips/bin/vc | uniq
SOURCE
/sys/src/cmd/cwfs
SEE ALSO
yesterday(1), fs(3), sd(3), fs(4), srv(4), fs(8),
fsconfig(8)
Sean Quinlan, ``A Cached WORM File System'', Software -
Practice and Experience, December, 1991
Ken Thompson, Geoff Collyer, ``The 64-bit Standalone Plan 9
File Server''
BUGS
For the moment, the file server serves both the old (9P1)
and new (9P2000) versions of 9P, deciding which to serve by
sniffing the first packet on each connection.
File system block size and disk address size (32- or 64-bit)
are fixed at compilation time, and this is not easily
changed.
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