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).

ARGUMENTS

q Pointer to the queue.

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

DESCRIPTION

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

CONTEXT

qreply() can be called from user or interrupt context.

EXAMPLE

This example depicts the canonical flushing code for STREAMS drivers. Assume that the driver has service procedures (see srv(9E)), so that there may be messages on its queues. Its write-side put procedure (see put(9E)) 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). 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(9F) 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 {
5switch(mp->b_datap->db_type) {
6case M_FLUSH:
7if (∗mp->b_rptr & FLUSHW) {
8flushq(q, FLUSHALL);
9∗mp->b_rptr &= ~FLUSHW;
10}
11if (∗mp->b_rptr & FLUSHR) {
12flushq(RD(q), FLUSHALL);
13qreply(q, mp);
14} else {
15freemsg(mp);
16}
17break;
. . .
18}
19 }

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