DK(3) 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 circuit, named 0 through 255, and a special
file named clone. The specifier name matches the Datakit
device to a physical device that its virtual 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 network. The routines expect the
following properties of any multiplexed network, not just
Datakit.
Opening the clone file opens the ctl file of an unused vir-
tual 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 con-
nection, 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 appli-
cable)
To set up and tear down virtual circuits a process writes
textual commands to the ctl file:
Page 1 Plan 9 (printed 11/18/24)
DK(3) DK(3)
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 direc-
tory. 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 cir-
cuit.
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 mul-
tiplexed connection to a Datakit. The subsequent config
control message configures 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 cho-
sen by Datakit)
[no]restart
the word restart or norestart (optional; default is
restart). Restart tells the Datakit to forget all pre-
vious connections and authentications for this machine.
name The name used in binding dk device.
window
the default URP window size for virtual circuits on
Page 2 Plan 9 (printed 11/18/24)
DK(3) DK(3)
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
Page 3 Plan 9 (printed 11/18/24)