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

qwait, qwait_sig - STREAMS wait routines

#include <sys/stream.h>
#include <sys/ddi.h>
void qwait(queue_t *q);

int qwait_sig(queue_t *q);

illumos DDI specific (illumos DDI).

Pointer to the queue that is being opened or closed.

qwait() and qwait_sig() are used to wait for a message to arrive to the put(9E) or srv(9E) procedures. qwait() and qwait_sig() can also be used to wait for qbufcall(9F) or qtimeout(9F) callback procedures to execute. These routines can be used in the open(9E) and close(9E) procedures in a STREAMS driver or module.

The thread that calls close() does not necessarily have the ability to receive signals, particularly when called by exit(2). In this case, qwait_sig() behaves exactly as qwait(). Driver writers may use ddi_can_receive_sig(9F) to determine when this is the case, and, if so, arrange some means to avoid blocking indefinitely (for example, by using qtimeout(9F).

qwait() and qwait_sig() atomically exit the inner and outer perimeters associated with the queue, and wait for a thread to leave the module's put(9E), srv(9E), or qbufcall(9F) / qtimeout(9F) callback procedures. Upon return they re-enter the inner and outer perimeters.

This can be viewed as there being an implicit wakeup when a thread leaves a put(9E) or srv(9E) procedure or after a qtimeout(9F) or qbufcall(9F) callback procedure has been run in the same perimeter.

qprocson(9F) must be called before calling qwait() or qwait_sig().

qwait() is not interrupted by a signal, whereas qwait_sig() is interrupted by a signal. qwait_sig() normally returns non-zero, and returns zero when the waiting was interrupted by a signal.

qwait() and qwait_sig() are similar to cv_wait() and cv_wait_sig() except that the mutex is replaced by the inner and outer perimeters and the signalling is implicit when a thread leaves the inner perimeter. See condvar(9F).

For qwait_sig(), indicates that the condition was not necessarily signaled, and the function returned because a signal was pending.

These functions can only be called from an open(9E) or close(9E) routine.

Example 1 Using qwait()

The open routine sends down a T_INFO_REQ message and waits for the T_INFO_ACK. The arrival of the T_INFO_ACK is recorded by resetting a flag in the unit structure (WAIT_INFO_ACK). The example assumes that the module is D_MTQPAIR or D_MTPERMOD.

xxopen(qp, ...)
       queue_t *qp;
	      struct xxdata *xx;
	       /* Allocate xxdata structure */
       /* Format T_INFO_ACK in mp */
       putnext(qp, mp);
       xx->xx_flags |= WAIT_INFO_ACK;
       while (xx->xx_flags & WAIT_INFO_ACK)
	      return (0);
xxrput(qp, mp)
       queue_t *qp;
       mblk_t *mp;
       struct xxdata *xx = (struct xxdata *)q->q_ptr;
	      case T_INFO_ACK:
		            if (xx->xx_flags & WAIT_INFO_ACK) {
			              /* Record information from info ack */
			              xx->xx_flags &= ~WAIT_INFO_ACK;

close(9E), open(9E), put(9E), srv(9E), condvar(9F), ddi_can_receive_sig(9F), mt-streams(9F), qbufcall(9F), qprocson(9F), qtimeout(9F)

STREAMS Programming Guide

Writing Device Drivers

December 15, 2003 OmniOS