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/*	$OpenBSD: kern_time.c,v 1.62 2007/04/04 17:32:20 art Exp $	*/
/*	$NetBSD: kern_time.c,v 1.20 1996/02/18 11:57:06 fvdl Exp $	*/

/*
 * Copyright (c) 1982, 1986, 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_time.c	8.4 (Berkeley) 5/26/95
 */

#include <sys/param.h>
#include <sys/resourcevar.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/signalvar.h>
#ifdef __HAVE_TIMECOUNTER
#include <sys/timetc.h>
#endif

#include <sys/mount.h>
#include <sys/syscallargs.h>

#include <machine/cpu.h>

void	itimerround(struct timeval *);

/* 
 * Time of day and interval timer support.
 *
 * These routines provide the kernel entry points to get and set
 * the time-of-day and per-process interval timers.  Subroutines
 * here provide support for adding and subtracting timeval structures
 * and decrementing interval timers, optionally reloading the interval
 * timers when they expire.
 */

/* This function is used by clock_settime and settimeofday */
#ifdef __HAVE_TIMECOUNTER
int
settime(struct timespec *ts)
{
	struct timespec now;
	

	/*
	 * Don't allow the time to be set forward so far it will wrap
	 * and become negative, thus allowing an attacker to bypass
	 * the next check below.  The cutoff is 1 year before rollover
	 * occurs, so even if the attacker uses adjtime(2) to move
	 * the time past the cutoff, it will take a very long time
	 * to get to the wrap point.
	 *
	 * XXX: we check against INT_MAX since on 64-bit
	 *	platforms, sizeof(int) != sizeof(long) and
	 *	time_t is 32 bits even when atv.tv_sec is 64 bits.
	 */
	if (ts->tv_sec > INT_MAX - 365*24*60*60) {
		printf("denied attempt to set clock forward to %ld\n",
		    ts->tv_sec);
		return (EPERM);
	}
	/*
	 * If the system is secure, we do not allow the time to be
	 * set to an earlier value (it may be slowed using adjtime,
	 * but not set back). This feature prevent interlopers from
	 * setting arbitrary time stamps on files.
	 */
	nanotime(&now);
	if (securelevel > 1 && timespeccmp(ts, &now, <)) {
		printf("denied attempt to set clock back %ld seconds\n",
		    now.tv_sec - ts->tv_sec);
		return (EPERM);
	}

	tc_setclock(ts);
	resettodr();

	return (0);
}
#else
int
settime(struct timespec *ts)
{
	struct timeval delta, tvv, *tv;
	int s;

	/* XXX - Ugh. */
	tv = &tvv;
	tvv.tv_sec = ts->tv_sec;
	tvv.tv_usec = ts->tv_nsec / 1000;

	/*
	 * Don't allow the time to be set forward so far it will wrap
	 * and become negative, thus allowing an attacker to bypass
	 * the next check below.  The cutoff is 1 year before rollover
	 * occurs, so even if the attacker uses adjtime(2) to move
	 * the time past the cutoff, it will take a very long time
	 * to get to the wrap point.
	 *
	 * XXX: we check against INT_MAX since on 64-bit
	 *	platforms, sizeof(int) != sizeof(long) and
	 *	time_t is 32 bits even when atv.tv_sec is 64 bits.
	 */
	if (tv->tv_sec > INT_MAX - 365*24*60*60) {
		printf("denied attempt to set clock forward to %ld\n",
		    tv->tv_sec);
		return (EPERM);
	}
	/*
	 * If the system is secure, we do not allow the time to be
	 * set to an earlier value (it may be slowed using adjtime,
	 * but not set back). This feature prevent interlopers from
	 * setting arbitrary time stamps on files.
	 */
	if (securelevel > 1 && timercmp(tv, &time, <)) {
		printf("denied attempt to set clock back %ld seconds\n",
		    time_second - tv->tv_sec);
		return (EPERM);
	}

	/* WHAT DO WE DO ABOUT PENDING REAL-TIME TIMEOUTS??? */
	s = splclock();
	timersub(tv, &time, &delta);
	time = *tv;
	timeradd(&boottime, &delta, &boottime);
	splx(s);
	resettodr();

	return (0);
}
#endif

/* ARGSUSED */
int
sys_clock_gettime(struct proc *p, void *v, register_t *retval)
{
	struct sys_clock_gettime_args /* {
		syscallarg(clockid_t) clock_id;
		syscallarg(struct timespec *) tp;
	} */ *uap = v;
	clockid_t clock_id;
	struct timespec ats;

	clock_id = SCARG(uap, clock_id);
	switch (clock_id) {
	case CLOCK_REALTIME:
		nanotime(&ats);
		break;
	case CLOCK_MONOTONIC:
		nanouptime(&ats);
		break;
	case CLOCK_PROF:
		ats.tv_sec = p->p_rtime.tv_sec;
		ats.tv_nsec = p->p_rtime.tv_usec * 1000;
		break;
	default:
		return (EINVAL);
	}

	return copyout(&ats, SCARG(uap, tp), sizeof(ats));
}

/* ARGSUSED */
int
sys_clock_settime(struct proc *p, void *v, register_t *retval)
{
	struct sys_clock_settime_args /* {
		syscallarg(clockid_t) clock_id;
		syscallarg(const struct timespec *) tp;
	} */ *uap = v;
	struct timespec ats;
	clockid_t clock_id;
	int error;

	if ((error = suser(p, 0)) != 0)
		return (error);

	if ((error = copyin(SCARG(uap, tp), &ats, sizeof(ats))) != 0)
		return (error);

	clock_id = SCARG(uap, clock_id);
	switch (clock_id) {
	case CLOCK_REALTIME:
		if ((error = settime(&ats)) != 0)
			return (error);
		break;
	default:	/* Other clocks are read-only */
		return (EINVAL);
	}

	return (0);
}

int
sys_clock_getres(struct proc *p, void *v, register_t *retval)
{
	struct sys_clock_getres_args /* {
		syscallarg(clockid_t) clock_id;
		syscallarg(struct timespec *) tp;
	} */ *uap = v;
	clockid_t clock_id;
	struct timespec ts;
	int error = 0;

	clock_id = SCARG(uap, clock_id);
	switch (clock_id) {
	case CLOCK_REALTIME:
	case CLOCK_MONOTONIC:
		ts.tv_sec = 0;
		ts.tv_nsec = 1000000000 / hz;
		break;
	default:
		return (EINVAL);
	}

	if (SCARG(uap, tp))
		error = copyout(&ts, SCARG(uap, tp), sizeof (ts));

	return error;
}

/* ARGSUSED */
int
sys_nanosleep(struct proc *p, void *v, register_t *retval)
{
	static int nanowait;
	struct sys_nanosleep_args/* {
		syscallarg(const struct timespec *) rqtp;
		syscallarg(struct timespec *) rmtp;
	} */ *uap = v;
	struct timespec rqt, rmt;
	struct timespec sts, ets;
	struct timeval tv;
	int error;

	error = copyin((const void *)SCARG(uap, rqtp), (void *)&rqt,
	    sizeof(struct timespec));
	if (error)
		return (error);

	TIMESPEC_TO_TIMEVAL(&tv, &rqt);
	if (itimerfix(&tv))
		return (EINVAL);

	if (SCARG(uap, rmtp))
		getnanouptime(&sts);

	error = tsleep(&nanowait, PWAIT | PCATCH, "nanosleep",
	    MAX(1, tvtohz(&tv)));
	if (error == ERESTART)
		error = EINTR;
	if (error == EWOULDBLOCK)
		error = 0;

	if (SCARG(uap, rmtp)) {
		getnanouptime(&ets);

		timespecsub(&ets, &sts, &sts);
		timespecsub(&rqt, &sts, &rmt);

		if (rmt.tv_sec < 0)
			timespecclear(&rmt);

		error = copyout((void *)&rmt, (void *)SCARG(uap,rmtp),
		    sizeof(rmt));
	}

	return error;
}

/* ARGSUSED */
int
sys_gettimeofday(struct proc *p, void *v, register_t *retval)
{
	struct sys_gettimeofday_args /* {
		syscallarg(struct timeval *) tp;
		syscallarg(struct timezone *) tzp;
	} */ *uap = v;
	struct timeval atv;
	int error = 0;

	if (SCARG(uap, tp)) {
		microtime(&atv);
		if ((error = copyout((void *)&atv, (void *)SCARG(uap, tp),
		    sizeof (atv))))
			return (error);
	}
	if (SCARG(uap, tzp))
		error = copyout((void *)&tz, (void *)SCARG(uap, tzp),
		    sizeof (tz));
	return (error);
}

/* ARGSUSED */
int
sys_settimeofday(struct proc *p, void *v, register_t *retval)
{
	struct sys_settimeofday_args /* {
		syscallarg(const struct timeval *) tv;
		syscallarg(const struct timezone *) tzp;
	} */ *uap = v;
	struct timezone atz;
	struct timeval atv;
	int error;

	if ((error = suser(p, 0)))
		return (error);
	/* Verify all parameters before changing time. */
	if (SCARG(uap, tv) && (error = copyin((void *)SCARG(uap, tv),
	    (void *)&atv, sizeof(atv))))
		return (error);
	if (SCARG(uap, tzp) && (error = copyin((void *)SCARG(uap, tzp),
	    (void *)&atz, sizeof(atz))))
		return (error);
	if (SCARG(uap, tv)) {
		struct timespec ts;

		TIMEVAL_TO_TIMESPEC(&atv, &ts);
		if ((error = settime(&ts)) != 0)
			return (error);
	}
	if (SCARG(uap, tzp))
		tz = atz;
	return (0);
}

#ifdef __HAVE_TIMECOUNTER
struct timeval adjtimedelta;		/* unapplied time correction */
#else
int	tickdelta;			/* current clock skew, us. per tick */
long	timedelta;			/* unapplied time correction, us. */
long	bigadj = 1000000;		/* use 10x skew above bigadj us. */
int64_t	ntp_tick_permanent;
int64_t	ntp_tick_acc;
#endif

/* ARGSUSED */
int
sys_adjfreq(struct proc *p, void *v, register_t *retval)
{
	struct sys_adjfreq_args /* {
		syscallarg(const int64_t *) freq;
		syscallarg(int64_t *) oldfreq;
	} */ *uap = v;
	int error;
	int64_t f;
#ifndef __HAVE_TIMECOUNTER
	int s;

	if (SCARG(uap, oldfreq)) {
		f = ntp_tick_permanent * hz;
		if ((error = copyout((void *)&f, (void *)SCARG(uap, oldfreq),
		    sizeof(int64_t))))
			return (error);
	}
	if (SCARG(uap, freq)) {
		if ((error = suser(p, 0)))
			return (error);
		if ((error = copyin((void *)SCARG(uap, freq), (void *)&f,
		    sizeof(int64_t))))
			return (error);
		s = splclock();
		ntp_tick_permanent = f / hz;
		splx(s);
	}
#else
	if (SCARG(uap, oldfreq)) {
		if ((error = tc_adjfreq(&f, NULL)) != 0)
			return (error);
		if ((error = copyout(&f, SCARG(uap, oldfreq), sizeof(f))) != 0)
			return (error);
	}
	if (SCARG(uap, freq)) {
		if ((error = suser(p, 0)))
			return (error);
		if ((error = copyin(SCARG(uap, freq), &f, sizeof(f))) != 0)
			return (error);
		if ((error = tc_adjfreq(NULL, &f)) != 0)
			return (error);
	}
#endif
	return (0);
}

/* ARGSUSED */
int
sys_adjtime(struct proc *p, void *v, register_t *retval)
{
	struct sys_adjtime_args /* {
		syscallarg(const struct timeval *) delta;
		syscallarg(struct timeval *) olddelta;
	} */ *uap = v;
#ifdef __HAVE_TIMECOUNTER
	int error;

	if (SCARG(uap, olddelta))
		if ((error = copyout((void *)&adjtimedelta,
		    (void *)SCARG(uap, olddelta), sizeof(struct timeval))))
			return (error);

	if (SCARG(uap, delta)) {
		if ((error = suser(p, 0)))
			return (error);

		if ((error = copyin((void *)SCARG(uap, delta),
		    (void *)&adjtimedelta, sizeof(struct timeval))))
			return (error);
	}

	/* Normalize the correction. */
	while (adjtimedelta.tv_usec >= 1000000) {
		adjtimedelta.tv_usec -= 1000000;
		adjtimedelta.tv_sec += 1;
	}
	while (adjtimedelta.tv_usec < 0) {
		adjtimedelta.tv_usec += 1000000;
		adjtimedelta.tv_sec -= 1;
	}
	return (0);
#else
	struct timeval atv;
	long ndelta, ntickdelta, odelta;
	int s, error;

	if (!SCARG(uap, delta)) {
		s = splclock();
		odelta = timedelta;
		splx(s);
		goto out;
	}
	if ((error = suser(p, 0)))
		return (error);
	if ((error = copyin((void *)SCARG(uap, delta), (void *)&atv,
	    sizeof(struct timeval))))
		return (error);

	/*
	 * Compute the total correction and the rate at which to apply it.
	 * Round the adjustment down to a whole multiple of the per-tick
	 * delta, so that after some number of incremental changes in
	 * hardclock(), tickdelta will become zero, lest the correction
	 * overshoot and start taking us away from the desired final time.
	 */
	if (atv.tv_sec > LONG_MAX / 1000000L)
		ndelta = LONG_MAX;
	else if (atv.tv_sec < LONG_MIN / 1000000L)
		ndelta = LONG_MIN;
	else {
		ndelta = atv.tv_sec * 1000000L;
		odelta = ndelta;
		ndelta += atv.tv_usec;
		if (atv.tv_usec > 0 && ndelta <= odelta)
			ndelta = LONG_MAX;	
		else if (atv.tv_usec < 0 && ndelta >= odelta)
			ndelta = LONG_MIN;
	}

	if (ndelta > bigadj || ndelta < -bigadj)
		ntickdelta = 10 * tickadj;
	else
		ntickdelta = tickadj;
	if (ndelta % ntickdelta)
		ndelta = ndelta / ntickdelta * ntickdelta;

	/*
	 * To make hardclock()'s job easier, make the per-tick delta negative
	 * if we want time to run slower; then hardclock can simply compute
	 * tick + tickdelta, and subtract tickdelta from timedelta.
	 */
	if (ndelta < 0)
		ntickdelta = -ntickdelta;
	s = splclock();
	odelta = timedelta;
	timedelta = ndelta;
	tickdelta = ntickdelta;
	splx(s);

out:
	if (SCARG(uap, olddelta)) {
		atv.tv_sec = odelta / 1000000;
		atv.tv_usec = odelta % 1000000;
		if ((error = copyout((void *)&atv, (void *)SCARG(uap, olddelta),
		    sizeof(struct timeval))))
			return (error);
	}
	return (0);
#endif
}


/*
 * Get value of an interval timer.  The process virtual and
 * profiling virtual time timers are kept in the p_stats area, since
 * they can be swapped out.  These are kept internally in the
 * way they are specified externally: in time until they expire.
 *
 * The real time interval timer is kept in the process table slot
 * for the process, and its value (it_value) is kept as an
 * absolute time rather than as a delta, so that it is easy to keep
 * periodic real-time signals from drifting.
 *
 * Virtual time timers are processed in the hardclock() routine of
 * kern_clock.c.  The real time timer is processed by a timeout
 * routine, called from the softclock() routine.  Since a callout
 * may be delayed in real time due to interrupt processing in the system,
 * it is possible for the real time timeout routine (realitexpire, given below),
 * to be delayed in real time past when it is supposed to occur.  It
 * does not suffice, therefore, to reload the real timer .it_value from the
 * real time timers .it_interval.  Rather, we compute the next time in
 * absolute time the timer should go off.
 */
/* ARGSUSED */
int
sys_getitimer(struct proc *p, void *v, register_t *retval)
{
	struct sys_getitimer_args /* {
		syscallarg(int) which;
		syscallarg(struct itimerval *) itv;
	} */ *uap = v;
	struct itimerval aitv;
	int s;

	if (SCARG(uap, which) < ITIMER_REAL || SCARG(uap, which) > ITIMER_PROF)
		return (EINVAL);
	s = splclock();
	if (SCARG(uap, which) == ITIMER_REAL) {
		struct timeval now;

		getmicrouptime(&now);
		/*
		 * Convert from absolute to relative time in .it_value
		 * part of real time timer.  If time for real time timer
		 * has passed return 0, else return difference between
		 * current time and time for the timer to go off.
		 */
		aitv = p->p_realtimer;
		if (timerisset(&aitv.it_value)) {
			if (timercmp(&aitv.it_value, &now, <))
				timerclear(&aitv.it_value);
			else
				timersub(&aitv.it_value, &now,
				    &aitv.it_value);
		}
	} else
		aitv = p->p_stats->p_timer[SCARG(uap, which)];
	splx(s);
	return (copyout((void *)&aitv, (void *)SCARG(uap, itv),
	    sizeof (struct itimerval)));
}

/* ARGSUSED */
int
sys_setitimer(struct proc *p, void *v, register_t *retval)
{
	struct sys_setitimer_args /* {
		syscallarg(int) which;
		syscallarg(const struct itimerval *) itv;
		syscallarg(struct itimerval *) oitv;
	} */ *uap = v;
	struct sys_getitimer_args getargs;
	struct itimerval aitv;
	const struct itimerval *itvp;
	int error;
	int timo;

	if (SCARG(uap, which) < ITIMER_REAL || SCARG(uap, which) > ITIMER_PROF)
		return (EINVAL);
	itvp = SCARG(uap, itv);
	if (itvp && (error = copyin((void *)itvp, (void *)&aitv,
	    sizeof(struct itimerval))))
		return (error);
	if (SCARG(uap, oitv) != NULL) {
		SCARG(&getargs, which) = SCARG(uap, which);
		SCARG(&getargs, itv) = SCARG(uap, oitv);
		if ((error = sys_getitimer(p, &getargs, retval)))
			return (error);
	}
	if (itvp == 0)
		return (0);
	if (itimerfix(&aitv.it_value) || itimerfix(&aitv.it_interval))
		return (EINVAL);
	if (SCARG(uap, which) == ITIMER_REAL) {
		struct timeval ctv;

		timeout_del(&p->p_realit_to);
		getmicrouptime(&ctv);
		if (timerisset(&aitv.it_value)) {
			timo = tvtohz(&aitv.it_value);
			timeout_add(&p->p_realit_to, timo);
			timeradd(&aitv.it_value, &ctv, &aitv.it_value);
		}
		p->p_realtimer = aitv;
	} else {
		int s;

		itimerround(&aitv.it_interval);
		s = splclock();
		p->p_stats->p_timer[SCARG(uap, which)] = aitv;
		splx(s);
	}

	return (0);
}

/*
 * Real interval timer expired:
 * send process whose timer expired an alarm signal.
 * If time is not set up to reload, then just return.
 * Else compute next time timer should go off which is > current time.
 * This is where delay in processing this timeout causes multiple
 * SIGALRM calls to be compressed into one.
 */
void
realitexpire(void *arg)
{
	struct proc *p;

	p = (struct proc *)arg;
	psignal(p, SIGALRM);
	if (!timerisset(&p->p_realtimer.it_interval)) {
		timerclear(&p->p_realtimer.it_value);
		return;
	}
	for (;;) {
		struct timeval ctv, ntv;
		int timo;

		timeradd(&p->p_realtimer.it_value,
		    &p->p_realtimer.it_interval, &p->p_realtimer.it_value);
		getmicrouptime(&ctv);
		if (timercmp(&p->p_realtimer.it_value, &ctv, >)) {
			ntv = p->p_realtimer.it_value;
			timersub(&ntv, &ctv, &ntv);
			timo = tvtohz(&ntv) - 1;
			if (timo <= 0)
				timo = 1;
			if ((p->p_flag & P_WEXIT) == 0)
				timeout_add(&p->p_realit_to, timo);
			return;
		}
	}
}

/*
 * Check that a proposed value to load into the .it_value or
 * .it_interval part of an interval timer is acceptable.
 */
int
itimerfix(struct timeval *tv)
{

	if (tv->tv_sec < 0 || tv->tv_sec > 100000000 ||
	    tv->tv_usec < 0 || tv->tv_usec >= 1000000)
		return (EINVAL);

	if (tv->tv_sec == 0 && tv->tv_usec != 0 && tv->tv_usec < tick)
		tv->tv_usec = tick;

	return (0);
}

/*
 * Timer interval smaller than the resolution of the system clock are
 * rounded up.
 */
void
itimerround(struct timeval *tv)
{
	if (tv->tv_sec == 0 && tv->tv_usec < tick)
		tv->tv_usec = tick;
}

/*
 * Decrement an interval timer by a specified number
 * of microseconds, which must be less than a second,
 * i.e. < 1000000.  If the timer expires, then reload
 * it.  In this case, carry over (usec - old value) to
 * reduce the value reloaded into the timer so that
 * the timer does not drift.  This routine assumes
 * that it is called in a context where the timers
 * on which it is operating cannot change in value.
 */
int
itimerdecr(struct itimerval *itp, int usec)
{

	if (itp->it_value.tv_usec < usec) {
		if (itp->it_value.tv_sec == 0) {
			/* expired, and already in next interval */
			usec -= itp->it_value.tv_usec;
			goto expire;
		}
		itp->it_value.tv_usec += 1000000;
		itp->it_value.tv_sec--;
	}
	itp->it_value.tv_usec -= usec;
	usec = 0;
	if (timerisset(&itp->it_value))
		return (1);
	/* expired, exactly at end of interval */
expire:
	if (timerisset(&itp->it_interval)) {
		itp->it_value = itp->it_interval;
		itp->it_value.tv_usec -= usec;
		if (itp->it_value.tv_usec < 0) {
			itp->it_value.tv_usec += 1000000;
			itp->it_value.tv_sec--;
		}
	} else
		itp->it_value.tv_usec = 0;		/* sec is already 0 */
	return (0);
}

/*
 * ratecheck(): simple time-based rate-limit checking.  see ratecheck(9)
 * for usage and rationale.
 */
int
ratecheck(struct timeval *lasttime, const struct timeval *mininterval)
{
	struct timeval tv, delta;
	int rv = 0;

	microuptime(&tv);

	timersub(&tv, lasttime, &delta);

	/*
	 * check for 0,0 is so that the message will be seen at least once,
	 * even if interval is huge.
	 */
	if (timercmp(&delta, mininterval, >=) ||
	    (lasttime->tv_sec == 0 && lasttime->tv_usec == 0)) {
		*lasttime = tv;
		rv = 1;
	}

	return (rv);
}

/*
 * ppsratecheck(): packets (or events) per second limitation.
 */
int
ppsratecheck(struct timeval *lasttime, int *curpps, int maxpps)
{
	struct timeval tv, delta;
	int rv;

	microuptime(&tv);

	timersub(&tv, lasttime, &delta);

	/*
	 * check for 0,0 is so that the message will be seen at least once.
	 * if more than one second have passed since the last update of
	 * lasttime, reset the counter.
	 *
	 * we do increment *curpps even in *curpps < maxpps case, as some may
	 * try to use *curpps for stat purposes as well.
	 */
	if (maxpps == 0)
		rv = 0;
	else if ((lasttime->tv_sec == 0 && lasttime->tv_usec == 0) ||
	    delta.tv_sec >= 1) {
		*lasttime = tv;
		*curpps = 0;
		rv = 1;
	} else if (maxpps < 0)
		rv = 1;
	else if (*curpps < maxpps)
		rv = 1;
	else
		rv = 0;

#if 1 /*DIAGNOSTIC?*/
	/* be careful about wrap-around */
	if (*curpps + 1 > *curpps)
		*curpps = *curpps + 1;
#else
	/*
	 * assume that there's not too many calls to this function.
	 * not sure if the assumption holds, as it depends on *caller's*
	 * behavior, not the behavior of this function.
	 * IMHO it is wrong to make assumption on the caller's behavior,
	 * so the above #if is #if 1, not #ifdef DIAGNOSTIC.
	 */
	*curpps = *curpps + 1;
#endif

	return (rv);
}