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

       Solaris DDI specific (Solaris 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

SunOS 5.10							    1 Mar 1993							       qwriter(9F)