illumos: manual page: putbq.9f

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 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 component. 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().