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)