Function realtimer_settime

freebsd/kern/kern_time.c:1520–1567

}

static int
realtimer_settime(struct itimer *it, int flags,
	struct itimerspec *value, struct itimerspec *ovalue)
{
	struct timespec cts, ts;
	struct timeval tv;
	struct itimerspec val;

	mtx_assert(&it->it_mtx, MA_OWNED);

	val = *value;
	if (itimespecfix(&val.it_value))
		return (EINVAL);

	if (timespecisset(&val.it_value)) {
		if (itimespecfix(&val.it_interval))
			return (EINVAL);
	} else {
		timespecclear(&val.it_interval);
	}

	if (ovalue != NULL)
		realtimer_gettime(it, ovalue);

	it->it_time = val;
	if (timespecisset(&val.it_value)) {
		realtimer_clocktime(it->it_clockid, &cts);
		ts = val.it_value;
		if ((flags & TIMER_ABSTIME) == 0) {
			/* Convert to absolute time. */
			timespecadd(&it->it_time.it_value, &cts,
				&it->it_time.it_value);
		} else {
			timespecsub(&ts, &cts, &ts);
			/*
			 * We don't care if ts is negative, tztohz will
			 * fix it.
			 */
		}
		TIMESPEC_TO_TIMEVAL(&tv, &ts);
		callout_reset(&it->it_callout, tvtohz(&tv),
			realtimer_expire, it);
	} else {
		callout_stop(&it->it_callout);
	}

	return (0);
}

static void
realtimer_clocktime(clockid_t id, struct timespec *ts)