illumos: manual page: qreply.9f

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

NAME

qreply - send a message on a stream in the reverse direction

SYNOPSIS

#include <sys/stream.h>

void qreply(queue_t *q, mblk_t *mp);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI).

PARAMETERS

q
Pointer to the queue.

mp
Pointer to the message to be sent in the opposite direction.

DESCRIPTION

The qreply() function sends messages in the reverse direction of normal
flow. That is, qreply(q, mp) is equivalent to putnext(OTHERQ(q), mp).

CONTEXT

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

EXAMPLES

Example 1: Canonical Flushing Code for STREAMS Drivers.

This example depicts the canonical flushing code for STREAMS drivers.
Assume that the driver has service procedures so that there may be
messages on its queues. See srv(9E). Its write-side put procedure handles
M_FLUSH messages by first checking the FLUSHW bit in the first byte of
the message, then the write queue is flushed (line 8) and the FLUSHW bit
is turned off (line 9). See put(9E). If the FLUSHR bit is on, then the
read queue is flushed (line 12) and the message is sent back up the read
side of the stream with the qreply() function (line 13). If the FLUSHR
bit is off, then the message is freed (line 15). See the example for
flushq(9F) for the canonical flushing code for modules.

1 xxxwput(q, mp)
2 queue_t *q;
3 mblk_t *mp;
4 {
5 switch(mp->b_datap->db_type) {
6 case M_FLUSH:
7 if (*mp->b_rptr & FLUSHW) {
8 flushq(q, FLUSHALL);
9 *mp->b_rptr &= ~FLUSHW;
10 }
11 if (*mp->b_rptr & FLUSHR) {
12 flushq(RD(q), FLUSHALL);
13 qreply(q, mp);
14 } else {
15 freemsg(mp);
16 }
17 break;
...
18 }
19 }