Tribblix: 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 }