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
The putbq() function 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 priority 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 mes-
sage 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
The putbq() function returns 1 upon success and 0 upon failure.
Upon failure, the caller should call freemsg(9F) to free the pointer to the message block.
CONTEXT
The putbq() function can be called from user, interrupt, or kernel 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 5.11 16 Jan 2006 putbq(9F)