.TH STREAM 3 
.SH NAME
stream \- a structure for communications
.SH SYNOPSIS
.nf
.B x/data
.B x/ctl
.fi
.SH DESCRIPTION
.PP
A
.I stream
is not a device per se.
However, many devices use the
.I streams
package in the kernel to implement communications channels.
The properties described here are common to all such channels.
.PP
All streams are represented by two standard files,
.B ctl
and
.B data,
plus any others the particular device wants to add.
Reading and writing the
.B data
file receives and sends data on the channel.
If the channel is message oriented, each write
will represent a message and each read will
return at most one message.
If the buffer given in a read is smaller than the message,
subsequent reads will return the remainder of the message.
.PP
Writing textual command strings to the
.B ctl
file performs control operations on the stream.
The strings need not be null-terminated.
Each device may add to the control operations.
The common control operations are:
.TP 14
.B hangup
Hang up this stream.
Any subsequent writes will return an error.
The first subsequent read will return 0.
All following ones will return an error.
.TP 14
.BI push " name
Push the module 
.I name
onto the top of the stream.
.TP 14
.B pop
Pop the top module off the stream
.LP
Reading the 
.B ctl
file returns a textual identifier for the
stream.
This is used by multiplexed devices and its use
is described with the particular device.
.SH "SEE ALSO"
.IR pipe (3),
.IR dk (3),
.IR cons (3),
.IR async (3)