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

NAME

       putnextctl - send a control message to a queue

SYNOPSIS

       #include <sys/stream.h>

       int putnextctl(queue_t *q, int type);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       q	Queue to which the message is to be sent.

       type	Message type (must be control, not data type).

DESCRIPTION

       putnextctl()  tests the	type argument to make sure a data type has not been specified, and then attempts to allocate a message block. put-
       nextctl() fails if  type is  M_DATA, M_PROTO, or  M_PCPROTO, or if a message block cannot be allocated.	If successful,	putnextctl() calls
       the  put(9E) routine of the queue pointed to by	q with the newly allocated and initialized messages.

       A call to putnextctl(q,type) is an atomic equivalent of putctl(q->q_next,type). The STREAMS framework provides whatever mutual exclusion is
       necessary to insure that dereferencing q through its q_next field and then invoking putctl(9F) proceeds	without  interference  from  other
       threads.

       putnextctl() should always be used in preference to putctl(9F)

RETURN VALUES

       On success,  1 is returned. If  type is a data type, or if a message block cannot be allocated, 0 is returned.

CONTEXT

       putnextctl() can be called from user or interrupt context.

EXAMPLES

       The   send_ctl  routine	is  used  to  pass  control  messages  downstream.  M_BREAK messages are handled with  putnextctl() (line 8). put-
       nextctl1(9F) (line 13) is used for  M_DELAY messages,
	so that  parm can be used to specify the length of the delay. In either case, if a message block cannot be allocated  a  variable  record-
       ing  the number of allocation failures  is incremented (lines 9, 14).  If an invalid message type is detected,  cmn_err(9F) panics the sys-
       tem (line 18).

	1  void
	2  send_ctl(queue_t *wrq, uchar_t type, uchar_t parm)
	3  {
	4		extern int num_alloc_fail;
	5
	6		switch (type) {
	7	      case M_BREAK:
	8		     if (!putnextctl(wrq, M_BREAK))
	9				num_alloc_fail++;
       10		       break;
       11
       12		case M_DELAY:
       13		     if (!putnextctl1(wrq, M_DELAY, parm))
       14				num_alloc_fail++;
       15		     break;
       16
       17	      default:
       18		     cmn_err(CE_PANIC, "send_ctl: bad message type passed");
       19		       break;
       20		}
       21  }

SEE ALSO

       put(9E), cmn_err(9F), datamsg(9F), putctl(9F), putnextctl1(9F)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.10							    29 Mar 1993 						    putnextctl(9F)