illumos: manual page: flushq.9f

FLUSHQ(9F) Kernel Functions for Drivers FLUSHQ(9F)

NAME

flushq - remove messages from a queue

SYNOPSIS

#include <sys/stream.h>

void flushq(queue_t *q, int flag);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI).

PARAMETERS

q
Pointer to the queue to be flushed.

flag
Valid flag values are:

FLUSHDATA
Flush only data messages (types M_DATA M_DELAY M_PROTO and
M_PCPROTO).

FLUSHALL
Flush all messages.

DESCRIPTION

The flushq() function frees messages and their associated data structures
by calling freemsg(9F). If the queue's count falls below the low water
mark and the queue was blocking an upstream service procedure, the
nearest upstream service procedure is enabled.

CONTEXT

The flushq() function can be called from user, interrupt, or kernel
context.

EXAMPLES

Example 1: Using flushq()

This example depicts the canonical flushing code for STREAMS modules. The
module has a write service procedure and potentially has messages on the
queue. If it receives an M_FLUSH message, and if the FLUSHR bit is on in
the first byte of the message (line 10), then the read queue is flushed
(line 11). If the FLUSHW bit is on (line 12), then the write queue is
flushed (line 13). Then the message is passed along to the next entity in
the stream (line 14). See the example for qreply(9F) for the canonical
flushing code for drivers.

1 /*
2 * Module write-side put procedure.
3 */
4 xxxwput(q, mp)
5 queue_t *q;
6 mblk_t *mp;
7 {
8 switch(mp->b_datap->db_type) {
9 case M_FLUSH:
10 if (*mp->b_rptr & FLUSHR)
11 flushq(RD(q), FLUSHALL);
12 if (*mp->b_rptr & FLUSHW)
13 flushq(q, FLUSHALL);
14 putnext(q, mp);
15 break;
...
16 }
17 }