CWFS(4)                                                   CWFS(4)

          cwfs, cwfs64, cwfs64x, fs64 - cached-worm file server, dump

          cwfs [ -csC ] [ -n service ] [ -a announce-string ] ... [ -m
          device-map ] [ -f config-device ]

          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

          Options are:

          -f   specify config-device other than the default

          -a   announce on announce-string, can be specified multiple

          -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-

          -s   Post file descriptor zero in /srv/service and read and
               write protocol messages on file descriptor one.

     Page 1                       Plan 9             (printed 7/23/24)

     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

          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.

               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

          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

     Page 2                       Plan 9             (printed 7/23/24)

     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

          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%

     Page 3                       Plan 9             (printed 7/23/24)

     CWFS(4)                                                   CWFS(4)

          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-

               ls -lp /n/dump/1992/02??/mips/bin/vc | uniq


          yesterday(1), fs(3), sd(3), fs(4), srv(4), fs(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''

          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

     Page 4                       Plan 9             (printed 7/23/24)