[unix-history] / sys / kern / kern_time.c

/*
 * Copyright (c) 1982, 1986, 1989 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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	7.15 (Berkeley) 3/17/91
 */

#include "param.h"
#include "resourcevar.h"
#include "kernel.h"
#include "proc.h"

#include "machine/cpu.h"

/* 
 * 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.
 */

struct gettimeofday_args {
	struct	timeval *tp;
	struct	timezone *tzp;
};

/* ARGSUSED */
gettimeofday(p, uap, retval)
	struct proc *p;
	register struct gettimeofday_args *uap;
	int *retval;
{
	struct timeval atv;
	int error = 0;

	if (uap->tp) {
		microtime(&atv);
		if (error = copyout((caddr_t)&atv, (caddr_t)uap->tp,
		    sizeof (atv)))
			return (error);
	}
	if (uap->tzp)
		error = copyout((caddr_t)&tz, (caddr_t)uap->tzp,
		    sizeof (tz));
	return (error);
}

struct settimeofday_args {
	struct	timeval *tv;
	struct	timezone *tzp;
};

/* ARGSUSED */
settimeofday(p, uap, retval)
	struct proc *p;
	struct settimeofday_args *uap;
	int *retval;
{
	struct timeval atv;
	struct timezone atz;
	int error, s;

	if (error = suser(p->p_ucred, &p->p_acflag))
		return (error);
	if (uap->tv) {
		if (error = copyin((caddr_t)uap->tv, (caddr_t)&atv,
		    sizeof (struct timeval)))
			return (error);
		/* WHAT DO WE DO ABOUT PENDING REAL-TIME TIMEOUTS??? */
		boottime.tv_sec += atv.tv_sec - time.tv_sec;
		s = splhigh(); time = atv; splx(s);
		resettodr();
	}
	if (uap->tzp && (error = copyin((caddr_t)uap->tzp, (caddr_t)&atz,
	    sizeof (atz))) == 0)
		tz = atz;
	return (error);
}

extern	int tickadj;			/* "standard" clock skew, us./tick */
int	tickdelta;			/* current clock skew, us. per tick */
long	timedelta;			/* unapplied time correction, us. */
long	bigadj = 1000000;		/* use 10x skew above bigadj us. */

struct adjtime_args {
		struct timeval *delta;
		struct timeval *olddelta;
};

/* ARGSUSED */
adjtime(p, uap, retval)
	struct proc *p;
	register struct adjtime_args *uap;
	int *retval;
{
	struct timeval atv, oatv;
	register long ndelta;
	int s, error;

	if (error = suser(p->p_ucred, &p->p_acflag))
		return (error);
	if (error =
	    copyin((caddr_t)uap->delta, (caddr_t)&atv, sizeof (struct timeval)))
		return (error);
	ndelta = atv.tv_sec * 1000000 + atv.tv_usec;
	if (timedelta == 0)
		if (ndelta > bigadj)
			tickdelta = 10 * tickadj;
		else
			tickdelta = tickadj;
	if (ndelta % tickdelta)
		ndelta = ndelta / tickadj * tickadj;

	s = splclock();
	if (uap->olddelta) {
		oatv.tv_sec = timedelta / 1000000;
		oatv.tv_usec = timedelta % 1000000;
	}
	timedelta = ndelta;
	splx(s);

	if (uap->olddelta)
		(void) copyout((caddr_t)&oatv, (caddr_t)uap->olddelta,
			sizeof (struct timeval));
	return (0);
}

/*
 * 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.
 */

struct getitimer_args {
		u_int	which;
		struct	itimerval *itv;
};

/* ARGSUSED */
getitimer(p, uap, retval)
	struct proc *p;
	register struct getitimer_args *uap;
	int *retval;
{
	struct itimerval aitv;
	int s;

	if (uap->which > ITIMER_PROF)
		return (EINVAL);
	s = splclock();
	if (uap->which == ITIMER_REAL) {
		/*
		 * Convert from absoulte 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, &time, <))
				timerclear(&aitv.it_value);
			else
				timevalsub(&aitv.it_value, &time);
	} else
		aitv = p->p_stats->p_timer[uap->which];
	splx(s);
	return (copyout((caddr_t)&aitv, (caddr_t)uap->itv,
	    sizeof (struct itimerval)));
}

struct setitimer_args {
	u_int	which;
	struct	itimerval *itv, *oitv;
};

/* ARGSUSED */
setitimer(p, uap, retval)
	struct proc *p;
	register struct setitimer_args *uap;
	int *retval;
{
	struct itimerval aitv;
	register struct itimerval *itvp;
	int s, error;

	if (uap->which > ITIMER_PROF)
		return (EINVAL);
	itvp = uap->itv;
	if (itvp && (error = copyin((caddr_t)itvp, (caddr_t)&aitv,
	    sizeof(struct itimerval))))
		return (error);
	if ((uap->itv = uap->oitv) && (error = getitimer(p, uap, retval)))
		return (error);
	if (itvp == 0)
		return (0);
	if (itimerfix(&aitv.it_value) || itimerfix(&aitv.it_interval))
		return (EINVAL);
	s = splclock();
	if (uap->which == ITIMER_REAL) {
		untimeout(realitexpire, (caddr_t)p);
		if (timerisset(&aitv.it_value)) {
			timevaladd(&aitv.it_value, &time);
			timeout(realitexpire, (caddr_t)p, hzto(&aitv.it_value));
		}
		p->p_realtimer = aitv;
	} else
		p->p_stats->p_timer[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.
 */
realitexpire(p)
	register struct proc *p;
{
	int s;

	psignal(p, SIGALRM);
	if (!timerisset(&p->p_realtimer.it_interval)) {
		timerclear(&p->p_realtimer.it_value);
		return;
	}
	for (;;) {
		s = splclock();
		timevaladd(&p->p_realtimer.it_value,
		    &p->p_realtimer.it_interval);
		if (timercmp(&p->p_realtimer.it_value, &time, >)) {
			timeout(realitexpire, (caddr_t)p,
			    hzto(&p->p_realtimer.it_value));
			splx(s);
			return;
		}
		splx(s);
	}
}

/*
 * Check that a proposed value to load into the .it_value or
 * .it_interval part of an interval timer is acceptable, and
 * fix it to have at least minimal value (i.e. if it is less
 * than the resolution of the clock, round it up.)
 */
itimerfix(tv)
	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);
}

/*
 * 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
 * reducint 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.
 */
itimerdecr(itp, usec)
	register 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);
}

/*
 * Add and subtract routines for timevals.
 * N.B.: subtract routine doesn't deal with
 * results which are before the beginning,
 * it just gets very confused in this case.
 * Caveat emptor.
 */
timevaladd(t1, t2)
	struct timeval *t1, *t2;
{

	t1->tv_sec += t2->tv_sec;
	t1->tv_usec += t2->tv_usec;
	timevalfix(t1);
}

timevalsub(t1, t2)
	struct timeval *t1, *t2;
{

	t1->tv_sec -= t2->tv_sec;
	t1->tv_usec -= t2->tv_usec;
	timevalfix(t1);
}

timevalfix(t1)
	struct timeval *t1;
{

	if (t1->tv_usec < 0) {
		t1->tv_sec--;
		t1->tv_usec += 1000000;
	}
	if (t1->tv_usec >= 1000000) {
		t1->tv_sec++;
		t1->tv_usec -= 1000000;
	}
}
Commit	Line	Data
15637ed4 RG	1	/*
	2	* Copyright (c) 1982, 1986, 1989 Regents of the University of California.
	3	* All rights reserved.
	4	*
	5	* Redistribution and use in source and binary forms, with or without
	6	* modification, are permitted provided that the following conditions
	7	* are met:
	8	* 1. Redistributions of source code must retain the above copyright
	9	* notice, this list of conditions and the following disclaimer.
	10	* 2. Redistributions in binary form must reproduce the above copyright
	11	* notice, this list of conditions and the following disclaimer in the
	12	* documentation and/or other materials provided with the distribution.
	13	* 3. All advertising materials mentioning features or use of this software
	14	* must display the following acknowledgement:
	15	* This product includes software developed by the University of
	16	* California, Berkeley and its contributors.
	17	* 4. Neither the name of the University nor the names of its contributors
	18	* may be used to endorse or promote products derived from this software
	19	* without specific prior written permission.
	20	*
	21	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	22	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	23	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	24	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	25	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	26	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	27	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	28	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	29	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	30	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	31	* SUCH DAMAGE.
	32	*
	33	* @(#)kern_time.c 7.15 (Berkeley) 3/17/91
	34	*/
	35
	36	#include "param.h"
	37	#include "resourcevar.h"
	38	#include "kernel.h"
	39	#include "proc.h"
	40
	41	#include "machine/cpu.h"
	42
	43	/*
	44	* Time of day and interval timer support.
	45	*
	46	* These routines provide the kernel entry points to get and set
	47	* the time-of-day and per-process interval timers. Subroutines
	48	* here provide support for adding and subtracting timeval structures
	49	* and decrementing interval timers, optionally reloading the interval
	50	* timers when they expire.
	51	*/
	52
3c7eb27c DG	53	struct gettimeofday_args {
	54	struct timeval *tp;
	55	struct timezone *tzp;
	56	};
	57
15637ed4 RG	58	/* ARGSUSED */
	59	gettimeofday(p, uap, retval)
	60	struct proc *p;
3c7eb27c	61	register struct gettimeofday_args *uap;
15637ed4 RG	62	int *retval;
	63	{
	64	struct timeval atv;
	65	int error = 0;
	66
	67	if (uap->tp) {
	68	microtime(&atv);
	69	if (error = copyout((caddr_t)&atv, (caddr_t)uap->tp,
	70	sizeof (atv)))
	71	return (error);
	72	}
	73	if (uap->tzp)
	74	error = copyout((caddr_t)&tz, (caddr_t)uap->tzp,
	75	sizeof (tz));
	76	return (error);
	77	}
	78
3c7eb27c DG	79	struct settimeofday_args {
	80	struct timeval *tv;
	81	struct timezone *tzp;
	82	};
	83
15637ed4 RG	84	/* ARGSUSED */
	85	settimeofday(p, uap, retval)
	86	struct proc *p;
3c7eb27c	87	struct settimeofday_args *uap;
15637ed4 RG	88	int *retval;
	89	{
	90	struct timeval atv;
	91	struct timezone atz;
	92	int error, s;
	93
	94	if (error = suser(p->p_ucred, &p->p_acflag))
	95	return (error);
	96	if (uap->tv) {
	97	if (error = copyin((caddr_t)uap->tv, (caddr_t)&atv,
	98	sizeof (struct timeval)))
	99	return (error);
	100	/* WHAT DO WE DO ABOUT PENDING REAL-TIME TIMEOUTS??? */
	101	boottime.tv_sec += atv.tv_sec - time.tv_sec;
	102	s = splhigh(); time = atv; splx(s);
	103	resettodr();
	104	}
	105	if (uap->tzp && (error = copyin((caddr_t)uap->tzp, (caddr_t)&atz,
	106	sizeof (atz))) == 0)
	107	tz = atz;
	108	return (error);
	109	}
	110
	111	extern int tickadj; /* "standard" clock skew, us./tick */
	112	int tickdelta; /* current clock skew, us. per tick */
	113	long timedelta; /* unapplied time correction, us. */
	114	long bigadj = 1000000; /* use 10x skew above bigadj us. */
	115
3c7eb27c DG	116	struct adjtime_args {
	117	struct timeval *delta;
	118	struct timeval *olddelta;
	119	};
	120
15637ed4 RG	121	/* ARGSUSED */
	122	adjtime(p, uap, retval)
	123	struct proc *p;
3c7eb27c	124	register struct adjtime_args *uap;
15637ed4 RG	125	int *retval;
	126	{
	127	struct timeval atv, oatv;
	128	register long ndelta;
	129	int s, error;
	130
	131	if (error = suser(p->p_ucred, &p->p_acflag))
	132	return (error);
	133	if (error =
	134	copyin((caddr_t)uap->delta, (caddr_t)&atv, sizeof (struct timeval)))
	135	return (error);
	136	ndelta = atv.tv_sec * 1000000 + atv.tv_usec;
	137	if (timedelta == 0)
	138	if (ndelta > bigadj)
	139	tickdelta = 10 * tickadj;
	140	else
	141	tickdelta = tickadj;
	142	if (ndelta % tickdelta)
	143	ndelta = ndelta / tickadj * tickadj;
	144
	145	s = splclock();
	146	if (uap->olddelta) {
	147	oatv.tv_sec = timedelta / 1000000;
	148	oatv.tv_usec = timedelta % 1000000;
	149	}
	150	timedelta = ndelta;
	151	splx(s);
	152
	153	if (uap->olddelta)
	154	(void) copyout((caddr_t)&oatv, (caddr_t)uap->olddelta,
	155	sizeof (struct timeval));
	156	return (0);
	157	}
	158
	159	/*
	160	* Get value of an interval timer. The process virtual and
	161	* profiling virtual time timers are kept in the p_stats area, since
	162	* they can be swapped out. These are kept internally in the
	163	* way they are specified externally: in time until they expire.
	164	*
	165	* The real time interval timer is kept in the process table slot
	166	* for the process, and its value (it_value) is kept as an
	167	* absolute time rather than as a delta, so that it is easy to keep
	168	* periodic real-time signals from drifting.
	169	*
	170	* Virtual time timers are processed in the hardclock() routine of
	171	* kern_clock.c. The real time timer is processed by a timeout
	172	* routine, called from the softclock() routine. Since a callout
	173	* may be delayed in real time due to interrupt processing in the system,
	174	* it is possible for the real time timeout routine (realitexpire, given below),
	175	* to be delayed in real time past when it is supposed to occur. It
	176	* does not suffice, therefore, to reload the real timer .it_value from the
	177	* real time timers .it_interval. Rather, we compute the next time in
	178	* absolute time the timer should go off.
	179	*/
3c7eb27c DG	180
	181	struct getitimer_args {
	182	u_int which;
	183	struct itimerval *itv;
	184	};
	185
15637ed4 RG	186	/* ARGSUSED */
	187	getitimer(p, uap, retval)
	188	struct proc *p;
3c7eb27c	189	register struct getitimer_args *uap;
15637ed4 RG	190	int *retval;
	191	{
	192	struct itimerval aitv;
	193	int s;
	194
	195	if (uap->which > ITIMER_PROF)
	196	return (EINVAL);
	197	s = splclock();
	198	if (uap->which == ITIMER_REAL) {
	199	/*
	200	* Convert from absoulte to relative time in .it_value
	201	* part of real time timer. If time for real time timer
	202	* has passed return 0, else return difference between
	203	* current time and time for the timer to go off.
	204	*/
	205	aitv = p->p_realtimer;
	206	if (timerisset(&aitv.it_value))
	207	if (timercmp(&aitv.it_value, &time, <))
	208	timerclear(&aitv.it_value);
	209	else
	210	timevalsub(&aitv.it_value, &time);
	211	} else
	212	aitv = p->p_stats->p_timer[uap->which];
	213	splx(s);
	214	return (copyout((caddr_t)&aitv, (caddr_t)uap->itv,
	215	sizeof (struct itimerval)));
	216	}
	217
3c7eb27c DG	218	struct setitimer_args {
	219	u_int which;
	220	struct itimerval itv, oitv;
	221	};
	222
15637ed4 RG	223	/* ARGSUSED */
	224	setitimer(p, uap, retval)
	225	struct proc *p;
3c7eb27c	226	register struct setitimer_args *uap;
15637ed4 RG	227	int *retval;
	228	{
	229	struct itimerval aitv;
	230	register struct itimerval *itvp;
	231	int s, error;
	232
	233	if (uap->which > ITIMER_PROF)
	234	return (EINVAL);
	235	itvp = uap->itv;
	236	if (itvp && (error = copyin((caddr_t)itvp, (caddr_t)&aitv,
	237	sizeof(struct itimerval))))
	238	return (error);
	239	if ((uap->itv = uap->oitv) && (error = getitimer(p, uap, retval)))
	240	return (error);
	241	if (itvp == 0)
	242	return (0);
	243	if (itimerfix(&aitv.it_value) \|\| itimerfix(&aitv.it_interval))
	244	return (EINVAL);
	245	s = splclock();
	246	if (uap->which == ITIMER_REAL) {
	247	untimeout(realitexpire, (caddr_t)p);
	248	if (timerisset(&aitv.it_value)) {
	249	timevaladd(&aitv.it_value, &time);
	250	timeout(realitexpire, (caddr_t)p, hzto(&aitv.it_value));
	251	}
	252	p->p_realtimer = aitv;
	253	} else
	254	p->p_stats->p_timer[uap->which] = aitv;
	255	splx(s);
	256	return (0);
	257	}
	258
	259	/*
	260	* Real interval timer expired:
	261	* send process whose timer expired an alarm signal.
	262	* If time is not set up to reload, then just return.
	263	* Else compute next time timer should go off which is > current time.
	264	* This is where delay in processing this timeout causes multiple
	265	* SIGALRM calls to be compressed into one.
	266	*/
	267	realitexpire(p)
	268	register struct proc *p;
	269	{
	270	int s;
	271
	272	psignal(p, SIGALRM);
	273	if (!timerisset(&p->p_realtimer.it_interval)) {
	274	timerclear(&p->p_realtimer.it_value);
	275	return;
	276	}
	277	for (;;) {
	278	s = splclock();
	279	timevaladd(&p->p_realtimer.it_value,
	280	&p->p_realtimer.it_interval);
	281	if (timercmp(&p->p_realtimer.it_value, &time, >)) {
	282	timeout(realitexpire, (caddr_t)p,
	283	hzto(&p->p_realtimer.it_value));
	284	splx(s);
	285	return;
	286	}
	287	splx(s);
	288	}
	289	}
	290
291	/*
292	* Check that a proposed value to load into the .it_value or
293	* .it_interval part of an interval timer is acceptable, and
294	* fix it to have at least minimal value (i.e. if it is less
295	* than the resolution of the clock, round it up.)
296	*/
297	itimerfix(tv)
298	struct timeval *tv;
299	{
300
301	if (tv->tv_sec < 0 \|\| tv->tv_sec > 100000000 \|\|
302	tv->tv_usec < 0 \|\| tv->tv_usec >= 1000000)
303	return (EINVAL);
304	if (tv->tv_sec == 0 && tv->tv_usec != 0 && tv->tv_usec < tick)
305	tv->tv_usec = tick;
306	return (0);
307	}
308
309	/*
310	* Decrement an interval timer by a specified number
311	* of microseconds, which must be less than a second,
312	* i.e. < 1000000. If the timer expires, then reload
313	* it. In this case, carry over (usec - old value) to
314	* reducint the value reloaded into the timer so that
315	* the timer does not drift. This routine assumes
316	* that it is called in a context where the timers
317	* on which it is operating cannot change in value.
318	*/
319	itimerdecr(itp, usec)
320	register struct itimerval *itp;
321	int usec;
322	{
323
324	if (itp->it_value.tv_usec < usec) {
325	if (itp->it_value.tv_sec == 0) {
326	/* expired, and already in next interval */
327	usec -= itp->it_value.tv_usec;
328	goto expire;
329	}
330	itp->it_value.tv_usec += 1000000;
331	itp->it_value.tv_sec--;
332	}
333	itp->it_value.tv_usec -= usec;
334	usec = 0;
335	if (timerisset(&itp->it_value))
336	return (1);
337	/* expired, exactly at end of interval */
338	expire:
339	if (timerisset(&itp->it_interval)) {
340	itp->it_value = itp->it_interval;
341	itp->it_value.tv_usec -= usec;
342	if (itp->it_value.tv_usec < 0) {
343	itp->it_value.tv_usec += 1000000;
344	itp->it_value.tv_sec--;
345	}
346	} else
347	itp->it_value.tv_usec = 0; /* sec is already 0 */
348	return (0);
349	}
350
351	/*
352	* Add and subtract routines for timevals.
353	* N.B.: subtract routine doesn't deal with
354	* results which are before the beginning,
355	* it just gets very confused in this case.
356	* Caveat emptor.
357	*/
358	timevaladd(t1, t2)
359	struct timeval t1, t2;
360	{
361
362	t1->tv_sec += t2->tv_sec;
363	t1->tv_usec += t2->tv_usec;
364	timevalfix(t1);
365	}
366
367	timevalsub(t1, t2)
368	struct timeval t1, t2;
369	{
370
371	t1->tv_sec -= t2->tv_sec;
372	t1->tv_usec -= t2->tv_usec;
373	timevalfix(t1);
374	}
375
376	timevalfix(t1)
377	struct timeval *t1;
378	{
379
380	if (t1->tv_usec < 0) {
381	t1->tv_sec--;
382	t1->tv_usec += 1000000;
383	}
384	if (t1->tv_usec >= 1000000) {
385	t1->tv_sec++;
386	t1->tv_usec -= 1000000;
387	}
388	}