glenda.party
term% ls -F
term% pwd
$home/manuals/plan9_4th/3/fs
term% cat index.txt
FS(3)                      Library Functions Manual                      FS(3)



NAME
       fs - file system devices

SYNOPSIS
       bind -b #k /dev
       /dev/fs
       /dev/fs/ctl
       /dev/fs/...
       /dev/new

DESCRIPTION
       The fs driver builds complex disk files out of simpler disk files.  In‐
       spired by the Plan 9 file server  kernel's  configuration  strings,  it
       provides  device  mirroring, partitioning, interleaving, and catenation
       for disk-based services like fossil(4) or venti(8).

       The device is intended to be bound at /dev and initially contains a di‐
       rectory  named  fs,  which in turn contains a ctl file and one file per
       configured device.

       Most control messages introduce a new device, here named new.  The file
       arguments are interpreted in the name space of the writing process.

       The  device  name new may be a single filename component (containing no
       slashes); in this case, the device is created under #k/fs.  If new  in‐
       stead  has  the  format  dir/file,  the  device  is  made  available at
       #k/dir/file.  The directory dir goes away when the last device on it is
       removed with the del control message, but #k/fs will never be removed.

       cat new files...
              The device new corresponds to the catenation of files.

       inter new files...
              The  device  new corresponds to the block interleaving of files;
              an 8192-byte block size is assumed.

       mirror new files...
              The device new corresponds to a RAID-1-like mirroring of  files.
              Writes  to new are handled by sequentially writing the same data
              to the files from right to left (the reverse of the order in the
              control  message).   A failed write causes an eventual error re‐
              turn but does not prevent the rest of the writes  to  the  other
              devices  of  the  mirror set.  Reads from new are handled by se‐
              quentially reading from the files from left to right  until  one
              succeeds.  The length of the mirror device is the minimum of the
              lengths of the files.

       part new file offset length
       part new offset end
              In the first form, the device  new  corresponds  to  the  length
              units starting at offset in file.  If offset+length reaches past
              the end of file, length is silently reduced to fit.   Units  are
              bytes.   In  the  second form, a previous disk request must have
              defined the source file for further requests and the end of  the
              device  is  determined by the end offset in the source file, and
              not by the device length. Units are as defined in  the  previous
              disk request. This form is accepted for compatibility with fdisk
              (in prep(8)) and sd(3) devices.

       del old
              Removes the device named old.  The device  will  still  be  seen
              while  in use.  Further I/O attempts will fail with an error in‐
              dication stating that the device is gone.  When  old  is  dir/*,
              all devices under dir are removed.

       disk dir [ n file ]
              makes  dir implicit in new device names (i.e., it makes new mean
              dir/new by default).  Optional argument n specifies the  default
              unit (sector) size in bytes and the default source file for fur‐
              ther partition devices.  Default values are  restored  when  the
              control file is closed.

       clear  Discard all fs device definitions.

       If  the variable fsconfig is set in plan9.ini(8), fs will read its con‐
       figuration from the file $fsconfig on the first attach.  This is useful
       when the machine boots from a local file server that uses fs.

EXAMPLES
       Use  a  previously  partitioned disk, /dev/sdC0, making partition files
       available under /dev/sdC0parts:

              {
                   echo disk sdC0parts 512 /dev/sdC0/data
                   disk/fdisk -p /dev/sdC0/data
                   # now create plan 9 partitions
                   echo disk sdC0parts 512 /dev/sdC0parts/plan9
                   disk/prep -p /dev/sdC0parts/plan9
              } > /dev/fs/ctl

       Mirror the two disks /dev/sdC0/data and /dev/sdD0/data  as  /dev/fs/m0;
       similarly, mirror /dev/sdC1/data and /dev/sdD1/data as /dev/fs/m1:

              echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/fs/ctl
              echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/fs/ctl

       Interleave the two mirrored disks to create /dev/fs/data:

              echo inter data /dev/fs/m0 /dev/fs/m1 >/dev/fs/ctl

       Run kfs(4) on the interleaved device:

              disk/kfs -f /dev/fs/data

       Save the configuration:

              cp /dev/fs/ctl /dev/fd0disk

       To  load  the  configuration  automatically  at  boot time, add this to
       plan9.ini:

              fsconfig=/dev/fd0disk

SEE ALSO
       read in cat(1), dd(1), sd(3), fossil(4), fs(8), plan9.ini(8),  prep(8),
       venti(8)

SOURCE
       /sys/src/9/port/devfs.c

BUGS
       Mirrors  are RAID-like but not RAID.  There is no fancy recovery mecha‐
       nism and no automatic initial copying from a master drive to its mirror
       drives.

       Each write system call on ctl may transmit at most one command.



                                                                         FS(3)