bufcall man page on SmartOS

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BUFCALL(9F)							   BUFCALL(9F)

       bufcall - call a function when a buffer becomes available

       #include <sys/types.h>
       #include <sys/stream.h>

       bufcall_id_t bufcall(size_t size, uint_t pri, void *funcvoid *arg,
	   void *arg);

       Architecture independent level 1 (DDI/DKI).

	       Number of bytes required for the buffer.

	       Priority of the allocb(9F) allocation request (not used).

	       Function	 or  driver routine to be called when a buffer becomes

	       Argument to the function to be called  when  a  buffer  becomes

       The  bufcall()  function	 serves as a timeout(9F) call of indeterminate
       length. When a buffer allocation request fails, bufcall() can  be  used
       to schedule the routine func, to be called with the argument arg when a
       buffer becomes available. func may call allocb() or it may do something

       If  successful,	bufcall()  returns  a bufcall ID that can be used in a
       call to unbufcall() to cancel the request. If the bufcall()  scheduling
       fails, func is never called and 0 is returned.

       The  bufcall()  function	 can be called from user, interrupt, or kernel

       Example 1 Calling a function when a buffer becomes available:

       The purpose of this srv(9E) service routine is to add a header  to  all
       M_DATA  messages.  Service  routines must process all messages on their
       queues before returning, or arrange to be rescheduled

       While there are messages to be processed (line 13), check to see if  it
       is  a  high  priority  message or a normal priority message that can be
       sent on (line 14). Normal priority message that cannot be sent are  put
       back on the message queue (line 34). If the message was a high priority
       one, or if it was normal priority and  canputnext(9F)  succeeded,  then
       send  all but M_DATA messages to the next module with putnext(9F) (line

       For M_DATA messages, try to allocate a buffer large enough to hold  the
       header  (line  18). If no such buffer is available, the service routine
       must be rescheduled for a time when a buffer is available. The original
       message	is  put	 back  on the queue (line 20) and bufcall (line 21) is
       used to attempt the rescheduling. It will succeed if  the  rescheduling
       succeeds,  indicating that qenable will be called subsequently with the
       argument q once a buffer of the specified size  (sizeof	(struct	 hdr))
       becomes	available.  If	it does, qenable(9F) will put q on the list of
       queues to have their service routines called. If bufcall() fails, time‐
       out(9F) (line 22) is used to try again in about a half second.

       If  the	buffer allocation was successful, initialize the header (lines
       25-28), make the message type M_PROTO (line 29), link the  M_DATA  mes‐
       sage to it (line 30), and pass it on (line 31).

       Note  that  this	 example ignores the bookkeeping needed to handle buf‐
       call() and timeout(9F) cancellation for ones that are still outstanding
       at close time.

	  1  struct hdr {
	  2	unsigned int h_size;
	  3	int	     h_version;
	  4  };
	  6  void xxxsrv(q)
	  7	queue_t *q;
	  8  {
	  9	mblk_t *bp;
	 10	mblk_t *mp;
	 11	struct hdr *hp;
	 13	while ((mp = getq(q)) != NULL) { /* get next message */
	 14	    if (mp->b_datap->db_type >= QPCTL ||   /* if high priority */
			  canputnext(q)) {  /* normal & can be passed */
	 15	       if (mp->b_datap->db_type != M_DATA)
	 16		    putnext(q, mp); /* send all but M_DATA */
	 17	       else {
	 18		   bp = allocb(sizeof(struct hdr), BPRI_LO);
	 19		   if (bp == NULL) {	 /* if unsuccessful */
	 20			putbq(q, mp);	 /* put it back */
	 21			if (!bufcall(sizeof(struct hdr), BPRI_LO,
				    qenable, q)) /* try to reschedule */
	 22			    timeout(qenable, q, drv_usectohz(500000));
	 23			   return (0);
	 24		    }
	 25		    hp = (struct hdr *)bp->b_wptr;
	 26		    hp->h_size = msgdsize(mp);	   /* initialize header */
	 27		    hp->h_version = 1;
	 28		    bp->b_wptr += sizeof(struct hdr);
	 29		    bp->b_datap->db_type = M_PROTO;/* make M_PROTO  */
	 30		    bp->b_cont = mp;	 /* link it */
	 31		    putnext(q, bp); /* pass it on */
	 32	       }
	 33	    } else { /* normal priority, canputnext failed */
	 34	      putbq(q, mp);    /* put back on the message queue */
	 35	      return (0);
	 36	    }
	 37	   }
	      return (0);
	 38  }

       srv(9E),	 allocb(9F),  canputnext(9F), esballoc(9F), esbbcall(9F), put‐
       next(9F), qenable(9F), testb(9F), timeout(9F), unbufcall(9F)

       Writing Device Drivers

       STREAMS Programming Guide

       Even when func is called by bufcall(), allocb(9F) can fail  if  another
       module  or driver had allocated the memory before func was able to call

				 Jan 16, 2006			   BUFCALL(9F)

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