qwait(9F) Kernel Functions for Drivers qwait(9F)NAME
qwait, qwait_sig - STREAMS wait routines
SYNOPSIS
#include <sys/stream.h>
#include <sys/ddi.h>
void qwait(queue_t *q);
int qwait_sig(queue_t *q);
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI).
PARAMETERS
qp Pointer to the queue that is being opened or closed.
DESCRIPTIONqwait() 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 exe‐
cute. These routines can be used in the open(9E) and close(9E) proce‐
dures in a STREAMS driver or module.
Note - 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 qbuf‐
call(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 inter‐
rupted 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).
RETURN VALUES
0 For qwait_sig(), indicates that the condition was not neces‐
sarily signaled, and the function returned because a signal
was pending.
CONTEXT
These functions can only be called from an open(9E) or close(9E) rou‐
tine.
EXAMPLES
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 */
qprocson(qp);
/* Format T_INFO_ACK in mp */
putnext(qp, mp);
xx->xx_flags |= WAIT_INFO_ACK;
while (xx->xx_flags & WAIT_INFO_ACK)
qwait(qp);
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;
freemsg(mp);
return;
}
...
}
SEE ALSOclose(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
SunOS 5.10 15 Dec 2003 qwait(9F)
