A Datakit deviceeither
k
for the regular Datakit or
i
for the Inconis 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 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 commands 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 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 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).