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

NAME

       putbq - place a message at the head of a queue

SYNOPSIS

       #include <sys/stream.h>

       int putbq(queue_t *q, mblk_t *bp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       q	Pointer to the queue.

       bp	Pointer to the message block.

DESCRIPTION

       putbq()	places a message at the beginning of the appropriate section of the message queue. There are always sections for high priority and
       ordinary messages. If other priority bands are used, each will have its own section of the queue, in priority band order, after high prior-
       ity  messages  and  before  ordinary messages. putbq() can be used for ordinary, priority band, and high priority messages. However, unless
       precautions are taken, using putbq() with a high priority message is likely to lead to an infinite loop of putting the message back on  the
       queue, being rescheduled, pulling it off, and putting it back on.

       This  function  is  usually called when bcanput(9F) or canput(9F) determines that the message cannot be passed on to the next stream compo-
       nent. The flow control parameters are updated to reflect the change in the queue's status. If QNOENB is not set,  the  service  routine	is
       enabled.

RETURN VALUES

       putbq() returns 1 upon success and 0 upon failure.

       Note -  Upon failure, the caller should call freemsg(9F) to free the pointer to the message block.

CONTEXT

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

EXAMPLES

       See the bufcall(9F) function page for an example of putbq().

SEE ALSO

       bcanput(9F), bufcall(9F), canput(9F), getq(9F), putq(9F)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.10							    28 Aug 2001 							 putbq(9F)