insq

- insert a message into a queue

Synopsis

#include <sys/stream.h>

int insq(queue_t *q, mblk_t *emp, mblk_t *nmp);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

q

Pointer to the queue containing message emp.

emp

Enqueued message before which the new message is to be inserted. mblk_t is an instance of the msgb(9S) structure.

nmp

Message to be inserted.

Description

The insq() function inserts a message into a queue. The message to be inserted, nmp, is placed in q immediately before the message emp. If emp is NULL, the new message is placed at the end of the queue. The queue class of the new message is ignored. All flow control parameters are updated. The service procedure is enabled unless QNOENB is set.

Return Values

The insq() function returns 1 on success, and 0 on failure.

Context

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

Examples

This routine illustrates the steps a transport provider may take to place expedited data ahead of normal data on a queue (assume all M_DATA messages are converted into M_PROTO T_DATA_REQ messages). Normal T_DATA_REQ messages are just placed on the end of the queue (line 16). However, expedited T_EXDATA_REQ messages are inserted before any normal messages already on the queue (line 25). If there are no normal messages on the queue, bp will be NULL and we fall out of the for loop (line 21). insq acts like putq(9F) in this case.

 1  #include <sys/stream.h>
 2  #include <sys/tihdr.h>
 3
 4  static int
 5  xxxwput(queue_t *q, mblk_t *mp)
 6  {
 7   union T_primitives *tp;
 8   mblk_t *bp;
 9   union T_primitives *ntp;
10
11   switch (mp->b_datap->db_type) {
12   case M_PROTO:
13        tp = (union T_primitives *)mp->b_rptr;
14        switch (tp->type) {
15        case T_DATA_REQ:
16                putq(q, mp);
17                break;
18
19        case T_EXDATA_REQ:
20              /* Insert code here to protect queue and message block */
21               for (bp = q->q_first; bp; bp = bp->b_next) {
22                  if (bp->b_datap->db_type == M_PROTO) {
23                    ntp = (union T_primitives *)bp->b_rptr;
24                    if (ntp->type != T_EXDATA_REQ)
25                        break;
26                 }
27               }
28               (void)insq(q, bp, mp);
29               /* End of region that must be protected */
30               break;
          . . .
31              }
32    }
33   }

When using insq(), 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

putq(9F), rmvq(9F), msgb(9S)

Writing Device Drivers

STREAMS Programming Guide

Warnings

If emp is non-NULL, it must point to a message on q or a system panic could result.