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

NAME

qwriter - asynchronous STREAMS perimeter upgrade

SYNOPSIS

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


void qwriter(queue_t *qp, mblk_t *mp, void (*func)(), int perimeter);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

qp
Pointer to the queue.


mp
Pointer to a message that will be passed in to the
callback function.


func
A function that will be called when exclusive (writer)
access has been acquired at the specified perimeter.


perimeter
Either PERIM_INNER or PERIM_OUTER.

DESCRIPTION

qwriter() is used to upgrade the access at either the inner or the
outer perimeter from shared to exclusive and call the specified
callback function when the upgrade has succeeded. See mt-streams(9F).
The callback function is called as:

(*func)(queue_t *qp, mblk_t *mp);


qwriter() will acquire exclusive access immediately if possible, in
which case the specified callback function will be executed before
qwriter() returns. If this is not possible, qwriter() will defer the
upgrade until later and return before the callback function has been
executed. Modules should not assume that the callback function has
been executed when qwriter() returns. One way to avoid dependencies
on the execution of the callback function is to immediately return
after calling qwriter() and let the callback function finish the
processing of the message.


When qwriter() defers calling the callback function, the STREAMS
framework will prevent other messages from entering the inner
perimeter associated with the queue until the upgrade has completed
and the callback function has finished executing.

CONTEXT

qwriter() can only be called from an put(9E) or srv(9E) routine, or
from a qwriter(), qtimeout(9F), or qbufcall(9F) callback function.

SEE ALSO

put(9E), srv(9E), mt-streams(9F), qbufcall(9F), qtimeout(9F)


STREAMS Programming Guide


Writing Device Drivers

March 1, 1993 QWRITER(9F)