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man pages section 9: DDI and DKI Kernel Functions

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Updated: Thursday, June 13, 2019
 
 

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 or if the timeout handler calls this function on itself. 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 in Oracle Solaris 11.4