rmvq

- remove a message from a queue

Synopsis

#include <sys/stream.h>

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

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

q

Queue containing the message to be removed.

mp

Message to remove.

Description

The rmvq() function removes a message from a queue. A message can be removed from anywhere on a queue. To prevent modules and drivers from having to deal with the internals of message linkage on a queue, either rmvq() or getq(9F) should be used to remove a message from a queue.

Context

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

Examples

This code fragment illustrates how one may flush one type of message from a queue. In this case, only M_PROTO T_DATA_IND messages are flushed. For each message on the queue, if it is an M_PROTO message (line 8) of type T_DATA_IND (line 10), save a pointer to the next message (line 11), remove the T_DATA_IND message (line 12) and free it (line 13). Continue with the next message in the list (line 19).

1  mblk_t *mp, *nmp;
2  queue_t *q;
3  union T_primitives *tp;
4
5    /* Insert code here to protect queue and message block */
6    mp = q->q_first;
7    while (mp) {
8        if (mp->b_datap->db_type == M_PROTO) {
9            tp = (union T_primitives *)mp->b_rptr;
10            if (tp->type == T_DATA_IND) {
11                nmp = mp->b_next;
12                rmvq(q, mp);
13                freemsg(mp);
14                mp = nmp;
15            } else {
16                mp = mp->b_next;
17            }
18        } else {
19            mp = mp->b_next;
20        }
21    }
22    /* End of region that must be protected */

When using rmvq(), you must ensure that the queue and the message block is not modified by another thread at the same time. You can achieve this either by using STREAMS functions or by implementing your own locking.

See Also

freemsg(9F), getq(9F), insq(9F)

Writing Device Drivers

STREAMS Programming Guide

Warnings

Make sure that the message mp is linked onto q to avoid a possible system panic.