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

NAME

       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

       insq()  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

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

CONTEXT

       insq() can be called from user or interrupt 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
	     2	#include
	     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.

SunOS 5.10							    9 Jul 2001								  insq(9F)