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 should 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

SunOS 5.11							    16 Jan 2006 						     untimeout(9F)