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


NAME


untimeout - cancel previous timeout function call

SYNOPSIS


#include <sys/types.h>
#include <sys/conf.h>


clock_t untimeout(timeout_id_t id);


INTERFACE LEVEL


Architecture independent level 1 (DDI/DKI).

PARAMETERS


id
Opaque timeout ID from a previous timeout(9F) call.


DESCRIPTION


The untimeout() function cancels a pending timeout(9F) request.
untimeout() will not return until the pending callback is cancelled or
has run. Because of this, locks acquired by the callback routine must not
be held across the call to untimeout() or a deadlock may result.


Since no mutex should be held across the call to untimeout(), there is a
race condition between the occurrence of an expected event and the
execution of the timeout handler. In particular, it should be noted that
no problems will result from calling untimeout() for a timeout which is
either running on another CPU, or has already completed. Drivers should
be structured with the understanding that the arrival of both an
interrupt and a timeout for that interrupt can occasionally occur, in
either order.

RETURN VALUES


The untimeout() function returns -1 if the id is not found. Otherwise,
it returns an integer value greater than or equal to 0.

CONTEXT


The untimeout() function can be called from user, interrupt, or kernel
context.

EXAMPLES


In the following example, the device driver has issued an IO request and
is waiting for the device to respond. If the device does not respond
within 5 seconds, the device driver will print out an error message to
the console.

static void
xxtimeout_handler(void *arg)
{
struct xxstate *xsp = (struct xxstate *)arg;
mutex_enter(&xsp->lock);
cv_signal(&xsp->cv);
xsp->flags |= TIMED_OUT;
mutex_exit(&xsp->lock);
xsp->timeout_id = 0;
}
static uint_t
xxintr(caddr_t arg)
{
struct xxstate *xsp = (struct xxstate *)arg;
.
.
.
mutex_enter(&xsp->lock);
/* Service interrupt */
cv_signal(&xsp->cv);
mutex_exit(&xsp->lock);
if (xsp->timeout_id != 0) {
(void) untimeout(xsp->timeout_id);
xsp->timeout_id = 0;
}
return(DDI_INTR_CLAIMED);
}
static void
xxcheckcond(struct xxstate *xsp)
{
.
.
.
xsp->timeout_id = timeout(xxtimeout_handler,
xsp, (5 * drv_usectohz(1000000)));
mutex_enter(&xsp->lock);
while (/* Waiting for interrupt or timeout*/)
cv_wait(&xsp->cv, &xsp->lock);
if (xsp->flags & TIMED_OUT)
cmn_err(CE_WARN, "Device not responding");
.
.
.
mutex_exit(&xsp->lock);
.
.
.
}


SEE ALSO


open(9E), cv_signal(9F), cv_wait_sig(9F), delay(9F), timeout(9F)


Writing Device Drivers


February 12, 2014 UNTIMEOUT(9F)