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DK(3)                      Library Functions Manual                      DK(3)



NAME
       dk - Datakit conversations

SYNOPSIS
       bind #kname /net/dk
       bind #iname /net/dk

       ctlfd = open(".../ctl", ORDWR);
       write(ctlfd, "push dkmux", 10);
       write(ctlfd, "config csc [no]restart name nvc window", n);

DESCRIPTION
       A Datakit device--either k for the regular Datakit or i for the Incon--
       is a directory containing up to 256 directories, one per  virtual  cir-
       cuit,  named 0 through 255, and a special file named clone.  The speci-
       fier name matches the Datakit device to a physical device that its vir-
       tual circuits are multiplexed over (see dkmux below).

       Normally, the standard routines dial, hangup, listen, and announce (see
       dial(2)) are used to make, listen for, and control calls over any  net-
       work.   The routines expect the following properties of any multiplexed
       network, not just Datakit.

       Opening the clone file opens the ctl file of an unused virtual circuit.
       Reading any ctl file returns the name of the virtual circuit directory.
       For example, reading #k/17/ctl will return the string 17.

       Each virtual circuit directory contains the files:

       ctl       to control the virtual circuit: establish a connection,  hang
                 it up, etc.

       data      to converse with the remote end (via read and write)

       listen    to listen for calls (after announcing; see below)

       other     information about the conversation

       raddr     the address of the remote end

       ruser     the id of the user at the remote end (when applicable)

       To  set up and tear down virtual circuits a process writes textual com-
       mands to the ctl file:

       connect addr      connect to address addr.  If  the  connection  fails,
                         the write returns an error.

       hangup            tear down a connected virtual circuit.

       announce name     announce the readiness to accept calls to name.

       accept n          accept the call on virtual circuit n.

       reject n e        reject  the call on virtual circuit n with error code
                         e.  E must be a number from 0 to 7.

       Once a virtual circuit is set up,  a  process  can  converse  with  the
       remote  service by reading and writing the data file.  Write boundaries
       are preserved.

       Accepting calls to name requires the following dance:

       1)     announce name on a virtual circuit.

       2)     open the listen file in that virtual circuit's directory.   When
              a  call  comes  in  on a virtual circuit for name, the open will
              return with the file descriptor open to the control file of  the
              incoming virtual circuit.

       3)     accept or reject the call by writing an accept or reject command
              to the ctl file of the announced virtual circuit.

       A dkmux module pushed onto a stream makes  that  stream  a  multiplexed
       connection to a Datakit.  The subsequent config control message config-
       ures the multiplexer and matches it to a dk device.  The parameters  to
       the config message are

       csc    the line number of the common signaling channel (must be > 0)

       nvc    the  number  of  virtual  circuits  (optional; default chosen by
              Datakit)

       [no]restart
              the word restart or norestart (optional;  default  is  restart).
              Restart tells the Datakit to forget all previous connections and
              authentications for this machine.

       name   The name used in binding dk device.

       window the default URP window size for virtual circuits on this Datakit
              line (default is 2048).

FILES
       #k/clone
       #k/[0-255]
       #k/[0-255]/data
       #k/[0-255]/ctl
       #k/[0-255]/listen
       #k/[0-255]/ruser
       #k/[0-255]/raddr

SEE ALSO
       stream(3), dkconfig(8), datakit(3)

SOURCE
       /sys/src/9/*/devdk.c



                                                                         DK(3)