.if n .pH ddi.rm/d3/gen/pcmsg @(#)pcmsg	43.8 of 11/27/92
.\" Copyright 1991, 1992 UNIX System Laboratories, Inc.
.\" Copyright 1989 AT&T
.TH pcmsg D3
.IX "\f4pcmsg\fP(D3)"
.IX "STREAMS messages"
.SH NAME
\f4pcmsg\fP \- test whether a message is a priority control message
.SH SYNOPSIS
.nf
.na
.ft 4
#include <sys/types.h>
#include <sys/stream.h>
#include <sys/ddi.h>
.sp 0.4
int pcmsg(uchar_t \f2type\fP);
.ft 1
.ad
.fi
.SS Arguments
.RS 0
.IP "\f2type\fP" 10n
The type of message to be tested.
.RE
.SH DESCRIPTION
The \f4pcmsg\fP function tests the type of message to determine 
if it is a priority control message (also known as a high
priority message).
.SS "Return Values"
\f4pcmsg\fP returns 1
if the message is a priority control message and 0
if the message is any other type.
.SH USAGE
The \f4db_type\fP field of the \f4datab\fP(D4) structure
contains the message type.
This field may be accessed through the message block using
\f4mp->b_datap->db_type\fP.
.IX STREAMS messages
.SS Level
Base or Interrupt.
.SS "Synchronization Constraints"
Does not sleep.
.P
Driver-defined basic locks, read/write locks, and sleep locks may be
held across calls to this function.
.SS Examples
.IX "\f4pcmsg\fP(D3), example"
.IX "\f4putbq\fP(D3), example"
.IX "\f4putnext\fP(D3), example"
.P
The service routine processes messages on the queue.
If the message is a high priority message, or if it is a normal message and
the stream is not flow-controlled, the message is processed and passed
along in the stream.  Otherwise, the message is placed back on the
head of the queue and the service routine returns.
.P
.nf
.ft 4
.ps -1
.vs -1
 1    xxxsrv(q)
 2        queue_t *q;
 3    {
 4        mblk_t *mp;
.sp 0.4
 5        while ((mp = getq(q)) != NULL) {
 6            if (pcmsg(mp->b_datap->db_type) || canputnext(q->g_next)) {
 7                /* process message */
 8                putnext(q, mp);
 9            } else {
10                putbq(q, mp);
11                return;
12            }
13        }
14    }
.ft 1
.fi
.ps
.vs
.SH REFERENCES
.na
\f4allocb\fP(D3),
\f4datab\fP(D4),
\f4msgb\fP(D4),
\f4messages\fP(D5)
.ad