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INSQ(9F)							      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
       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  con‐
       text.

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  mes‐
       sages  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.

				 Mar 23, 2009			      INSQ(9F)
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