kernel - kqueue - refactor kqueue_scan(), rename tick to ustick

[dragonfly.git] / sys / kern / kern_time.c

/*
 * 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. 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 8.1 (Berkeley) 6/10/93
 * $FreeBSD: src/sys/kern/kern_time.c,v 1.68.2.1 2002/10/01 08:00:41 bde Exp $
 * $DragonFly: src/sys/kern/kern_time.c,v 1.40 2008/04/02 14:16:16 sephe Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/sysproto.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/sysent.h>
#include <sys/sysunion.h>
#include <sys/proc.h>
#include <sys/priv.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/sysctl.h>
#include <sys/kern_syscall.h>
#include <vm/vm.h>
#include <vm/vm_extern.h>

#include <sys/msgport2.h>
#include <sys/thread2.h>
#include <sys/mplock2.h>

struct timezone tz;

/*
 * 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.
 */

static int      nanosleep1(struct timespec *rqt, struct timespec *rmt);
static int      settime(struct timeval *);
static void     timevalfix(struct timeval *);

static int     sleep_hard_us = 100;
SYSCTL_INT(_kern, OID_AUTO, sleep_hard_us, CTLFLAG_RW, &sleep_hard_us, 0, "")

static int
settime(struct timeval *tv)
{
        struct timeval delta, tv1, tv2;
        static struct timeval maxtime, laststep;
        struct timespec ts;
        int origcpu;

        if ((origcpu = mycpu->gd_cpuid) != 0)
                lwkt_setcpu_self(globaldata_find(0));

        crit_enter();
        microtime(&tv1);
        delta = *tv;
        timevalsub(&delta, &tv1);

        /*
         * If the system is secure, we do not allow the time to be 
         * set to a value earlier than 1 second less than the highest
         * time we have yet seen. The worst a miscreant can do in
         * this circumstance is "freeze" time. He couldn't go
         * back to the past.
         *
         * We similarly do not allow the clock to be stepped more
         * than one second, nor more than once per second. This allows
         * a miscreant to make the clock march double-time, but no worse.
         */
        if (securelevel > 1) {
                if (delta.tv_sec < 0 || delta.tv_usec < 0) {
                        /*
                         * Update maxtime to latest time we've seen.
                         */
                        if (tv1.tv_sec > maxtime.tv_sec)
                                maxtime = tv1;
                        tv2 = *tv;
                        timevalsub(&tv2, &maxtime);
                        if (tv2.tv_sec < -1) {
                                tv->tv_sec = maxtime.tv_sec - 1;
                                kprintf("Time adjustment clamped to -1 second\n");
                        }
                } else {
                        if (tv1.tv_sec == laststep.tv_sec) {
                                crit_exit();
                                return (EPERM);
                        }
                        if (delta.tv_sec > 1) {
                                tv->tv_sec = tv1.tv_sec + 1;
                                kprintf("Time adjustment clamped to +1 second\n");
                        }
                        laststep = *tv;
                }
        }

        ts.tv_sec = tv->tv_sec;
        ts.tv_nsec = tv->tv_usec * 1000;
        set_timeofday(&ts);
        crit_exit();

        if (origcpu != 0)
                lwkt_setcpu_self(globaldata_find(origcpu));

        resettodr();
        return (0);
}

/*
 * MPSAFE
 */
int
kern_clock_gettime(clockid_t clock_id, struct timespec *ats)
{
        int error = 0;

        switch(clock_id) {
        case CLOCK_REALTIME:
                nanotime(ats);
                break;
        case CLOCK_MONOTONIC:
                nanouptime(ats);
                break;
        default:
                error = EINVAL;
                break;
        }
        return (error);
}

/*
 * MPSAFE
 */
int
sys_clock_gettime(struct clock_gettime_args *uap)
{
        struct timespec ats;
        int error;

        error = kern_clock_gettime(uap->clock_id, &ats);
        if (error == 0)
                error = copyout(&ats, uap->tp, sizeof(ats));

        return (error);
}

int
kern_clock_settime(clockid_t clock_id, struct timespec *ats)
{
        struct thread *td = curthread;
        struct timeval atv;
        int error;

        if ((error = priv_check(td, PRIV_CLOCK_SETTIME)) != 0)
                return (error);
        if (clock_id != CLOCK_REALTIME)
                return (EINVAL);
        if (ats->tv_nsec < 0 || ats->tv_nsec >= 1000000000)
                return (EINVAL);

        TIMESPEC_TO_TIMEVAL(&atv, ats);
        error = settime(&atv);
        return (error);
}

/*
 * MPALMOSTSAFE
 */
int
sys_clock_settime(struct clock_settime_args *uap)
{
        struct timespec ats;
        int error;

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

        get_mplock();
        error = kern_clock_settime(uap->clock_id, &ats);
        rel_mplock();
        return (error);
}

/*
 * MPSAFE
 */
int
kern_clock_getres(clockid_t clock_id, struct timespec *ts)
{
        int error;

        switch(clock_id) {
        case CLOCK_REALTIME:
        case CLOCK_MONOTONIC:
                /*
                 * Round up the result of the division cheaply
                 * by adding 1.  Rounding up is especially important
                 * if rounding down would give 0.  Perfect rounding
                 * is unimportant.
                 */
                ts->tv_sec = 0;
                ts->tv_nsec = 1000000000 / sys_cputimer->freq + 1;
                error = 0;
                break;
        default:
                error = EINVAL;
                break;
        }

        return(error);
}

/*
 * MPSAFE
 */
int
sys_clock_getres(struct clock_getres_args *uap)
{
        int error;
        struct timespec ts;

        error = kern_clock_getres(uap->clock_id, &ts);
        if (error == 0)
                error = copyout(&ts, uap->tp, sizeof(ts));

        return (error);
}

/*
 * nanosleep1()
 *
 *      This is a general helper function for nanosleep() (aka sleep() aka
 *      usleep()).
 *
 *      If there is less then one tick's worth of time left and
 *      we haven't done a yield, or the remaining microseconds is
 *      ridiculously low, do a yield.  This avoids having
 *      to deal with systimer overheads when the system is under
 *      heavy loads.  If we have done a yield already then use
 *      a systimer and an uninterruptable thread wait.
 *
 *      If there is more then a tick's worth of time left,
 *      calculate the baseline ticks and use an interruptable
 *      tsleep, then handle the fine-grained delay on the next
 *      loop.  This usually results in two sleeps occuring, a long one
 *      and a short one.
 *
 * MPSAFE
 */
static void
ns1_systimer(systimer_t info)
{
        lwkt_schedule(info->data);
}

static int
nanosleep1(struct timespec *rqt, struct timespec *rmt)
{
        static int nanowait;
        struct timespec ts, ts2, ts3;
        struct timeval tv;
        int error;
        int tried_yield;

        if (rqt->tv_nsec < 0 || rqt->tv_nsec >= 1000000000)
                return (EINVAL);
        if (rqt->tv_sec < 0 || (rqt->tv_sec == 0 && rqt->tv_nsec == 0))
                return (0);
        nanouptime(&ts);
        timespecadd(&ts, rqt);          /* ts = target timestamp compare */
        TIMESPEC_TO_TIMEVAL(&tv, rqt);  /* tv = sleep interval */
        tried_yield = 0;

        for (;;) {
                int ticks;
                struct systimer info;

                ticks = tv.tv_usec / ustick;    /* approximate */

                if (tv.tv_sec == 0 && ticks == 0) {
                        thread_t td = curthread;
                        if (tried_yield || tv.tv_usec < sleep_hard_us) {
                                tried_yield = 0;
                                uio_yield();
                        } else {
                                crit_enter_quick(td);
                                systimer_init_oneshot(&info, ns1_systimer,
                                                td, tv.tv_usec);
                                lwkt_deschedule_self(td);
                                crit_exit_quick(td);
                                lwkt_switch();
                                systimer_del(&info); /* make sure it's gone */
                        }
                        error = iscaught(td->td_lwp);
                } else if (tv.tv_sec == 0) {
                        error = tsleep(&nanowait, PCATCH, "nanslp", ticks);
                } else {
                        ticks = tvtohz_low(&tv); /* also handles overflow */
                        error = tsleep(&nanowait, PCATCH, "nanslp", ticks);
                }
                nanouptime(&ts2);
                if (error && error != EWOULDBLOCK) {
                        if (error == ERESTART)
                                error = EINTR;
                        if (rmt != NULL) {
                                timespecsub(&ts, &ts2);
                                if (ts.tv_sec < 0)
                                        timespecclear(&ts);
                                *rmt = ts;
                        }
                        return (error);
                }
                if (timespeccmp(&ts2, &ts, >=))
                        return (0);
                ts3 = ts;
                timespecsub(&ts3, &ts2);
                TIMESPEC_TO_TIMEVAL(&tv, &ts3);
        }
}

/*
 * MPSAFE
 */
int
sys_nanosleep(struct nanosleep_args *uap)
{
        int error;
        struct timespec rqt;
        struct timespec rmt;

        error = copyin(uap->rqtp, &rqt, sizeof(rqt));
        if (error)
                return (error);

        error = nanosleep1(&rqt, &rmt);

        /*
         * copyout the residual if nanosleep was interrupted.
         */
        if (error && uap->rmtp) {
                int error2;

                error2 = copyout(&rmt, uap->rmtp, sizeof(rmt));
                if (error2)
                        error = error2;
        }
        return (error);
}

/*
 * MPSAFE
 */
int
sys_gettimeofday(struct gettimeofday_args *uap)
{
        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);
}

/*
 * MPALMOSTSAFE
 */
int
sys_settimeofday(struct settimeofday_args *uap)
{
        struct thread *td = curthread;
        struct timeval atv;
        struct timezone atz;
        int error;

        if ((error = priv_check(td, PRIV_SETTIMEOFDAY)))
                return (error);
        /* Verify all parameters before changing time. */
        if (uap->tv) {
                if ((error = copyin((caddr_t)uap->tv, (caddr_t)&atv,
                    sizeof(atv))))
                        return (error);
                if (atv.tv_usec < 0 || atv.tv_usec >= 1000000)
                        return (EINVAL);
        }
        if (uap->tzp &&
            (error = copyin((caddr_t)uap->tzp, (caddr_t)&atz, sizeof(atz))))
                return (error);

        get_mplock();
        if (uap->tv && (error = settime(&atv))) {
                rel_mplock();
                return (error);
        }
        rel_mplock();
        if (uap->tzp)
                tz = atz;
        return (0);
}

static void
kern_adjtime_common(void)
{
        if ((ntp_delta >= 0 && ntp_delta < ntp_default_tick_delta) ||
            (ntp_delta < 0 && ntp_delta > -ntp_default_tick_delta))
                ntp_tick_delta = ntp_delta;
        else if (ntp_delta > ntp_big_delta)
                ntp_tick_delta = 10 * ntp_default_tick_delta;
        else if (ntp_delta < -ntp_big_delta)
                ntp_tick_delta = -10 * ntp_default_tick_delta;
        else if (ntp_delta > 0)
                ntp_tick_delta = ntp_default_tick_delta;
        else
                ntp_tick_delta = -ntp_default_tick_delta;
}

void
kern_adjtime(int64_t delta, int64_t *odelta)
{
        int origcpu;

        if ((origcpu = mycpu->gd_cpuid) != 0)
                lwkt_setcpu_self(globaldata_find(0));

        crit_enter();
        *odelta = ntp_delta;
        ntp_delta = delta;
        kern_adjtime_common();
        crit_exit();

        if (origcpu != 0)
                lwkt_setcpu_self(globaldata_find(origcpu));
}

static void
kern_get_ntp_delta(int64_t *delta)
{
        int origcpu;

        if ((origcpu = mycpu->gd_cpuid) != 0)
                lwkt_setcpu_self(globaldata_find(0));

        crit_enter();
        *delta = ntp_delta;
        crit_exit();

        if (origcpu != 0)
                lwkt_setcpu_self(globaldata_find(origcpu));
}

void
kern_reladjtime(int64_t delta)
{
        int origcpu;

        if ((origcpu = mycpu->gd_cpuid) != 0)
                lwkt_setcpu_self(globaldata_find(0));

        crit_enter();
        ntp_delta += delta;
        kern_adjtime_common();
        crit_exit();

        if (origcpu != 0)
                lwkt_setcpu_self(globaldata_find(origcpu));
}

static void
kern_adjfreq(int64_t rate)
{
        int origcpu;

        if ((origcpu = mycpu->gd_cpuid) != 0)
                lwkt_setcpu_self(globaldata_find(0));

        crit_enter();
        ntp_tick_permanent = rate;
        crit_exit();

        if (origcpu != 0)
                lwkt_setcpu_self(globaldata_find(origcpu));
}

/*
 * MPALMOSTSAFE
 */
int
sys_adjtime(struct adjtime_args *uap)
{
        struct thread *td = curthread;
        struct timeval atv;
        int64_t ndelta, odelta;
        int error;

        if ((error = priv_check(td, PRIV_ADJTIME)))
                return (error);
        error = copyin(uap->delta, &atv, sizeof(struct timeval));
        if (error)
                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.
         */
        ndelta = (int64_t)atv.tv_sec * 1000000000 + atv.tv_usec * 1000;
        get_mplock();
        kern_adjtime(ndelta, &odelta);
        rel_mplock();

        if (uap->olddelta) {
                atv.tv_sec = odelta / 1000000000;
                atv.tv_usec = odelta % 1000000000 / 1000;
                copyout(&atv, uap->olddelta, sizeof(struct timeval));
        }
        return (0);
}

static int
sysctl_adjtime(SYSCTL_HANDLER_ARGS)
{
        int64_t delta;
        int error;

        if (req->newptr != NULL) {
                if (priv_check(curthread, PRIV_ROOT))
                        return (EPERM);
                error = SYSCTL_IN(req, &delta, sizeof(delta));
                if (error)
                        return (error);
                kern_reladjtime(delta);
        }

        if (req->oldptr)
                kern_get_ntp_delta(&delta);
        error = SYSCTL_OUT(req, &delta, sizeof(delta));
        return (error);
}

/*
 * delta is in nanoseconds.
 */
static int
sysctl_delta(SYSCTL_HANDLER_ARGS)
{
        int64_t delta, old_delta;
        int error;

        if (req->newptr != NULL) {
                if (priv_check(curthread, PRIV_ROOT))
                        return (EPERM);
                error = SYSCTL_IN(req, &delta, sizeof(delta));
                if (error)
                        return (error);
                kern_adjtime(delta, &old_delta);
        }

        if (req->oldptr != NULL)
                kern_get_ntp_delta(&old_delta);
        error = SYSCTL_OUT(req, &old_delta, sizeof(old_delta));
        return (error);
}

/*
 * frequency is in nanoseconds per second shifted left 32.
 * kern_adjfreq() needs it in nanoseconds per tick shifted left 32.
 */
static int
sysctl_adjfreq(SYSCTL_HANDLER_ARGS)
{
        int64_t freqdelta;
        int error;

        if (req->newptr != NULL) {
                if (priv_check(curthread, PRIV_ROOT))
                        return (EPERM);
                error = SYSCTL_IN(req, &freqdelta, sizeof(freqdelta));
                if (error)
                        return (error);
                
                freqdelta /= hz;
                kern_adjfreq(freqdelta);
        }

        if (req->oldptr != NULL)
                freqdelta = ntp_tick_permanent * hz;
        error = SYSCTL_OUT(req, &freqdelta, sizeof(freqdelta));
        if (error)
                return (error);

        return (0);
}

SYSCTL_NODE(_kern, OID_AUTO, ntp, CTLFLAG_RW, 0, "NTP related controls");
SYSCTL_PROC(_kern_ntp, OID_AUTO, permanent,
    CTLTYPE_QUAD|CTLFLAG_RW, 0, 0,
    sysctl_adjfreq, "Q", "permanent correction per second");
SYSCTL_PROC(_kern_ntp, OID_AUTO, delta,
    CTLTYPE_QUAD|CTLFLAG_RW, 0, 0,
    sysctl_delta, "Q", "one-time delta");
SYSCTL_OPAQUE(_kern_ntp, OID_AUTO, big_delta, CTLFLAG_RD,
    &ntp_big_delta, sizeof(ntp_big_delta), "Q",
    "threshold for fast adjustment");
SYSCTL_OPAQUE(_kern_ntp, OID_AUTO, tick_delta, CTLFLAG_RD,
    &ntp_tick_delta, sizeof(ntp_tick_delta), "LU",
    "per-tick adjustment");
SYSCTL_OPAQUE(_kern_ntp, OID_AUTO, default_tick_delta, CTLFLAG_RD,
    &ntp_default_tick_delta, sizeof(ntp_default_tick_delta), "LU",
    "default per-tick adjustment");
SYSCTL_OPAQUE(_kern_ntp, OID_AUTO, next_leap_second, CTLFLAG_RW,
    &ntp_leap_second, sizeof(ntp_leap_second), "LU",
    "next leap second");
SYSCTL_INT(_kern_ntp, OID_AUTO, insert_leap_second, CTLFLAG_RW,
    &ntp_leap_insert, 0, "insert or remove leap second");
SYSCTL_PROC(_kern_ntp, OID_AUTO, adjust,
    CTLTYPE_QUAD|CTLFLAG_RW, 0, 0,
    sysctl_adjtime, "Q", "relative adjust for delta");

/*
 * 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.
 *
 * MPALMOSTSAFE
 */
int
sys_getitimer(struct getitimer_args *uap)
{
        struct proc *p = curproc;
        struct timeval ctv;
        struct itimerval aitv;

        if (uap->which > ITIMER_PROF)
                return (EINVAL);
        get_mplock();
        crit_enter();
        if (uap->which == ITIMER_REAL) {
                /*
                 * 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 (timevalisset(&aitv.it_value)) {
                        getmicrouptime(&ctv);
                        if (timevalcmp(&aitv.it_value, &ctv, <))
                                timevalclear(&aitv.it_value);
                        else
                                timevalsub(&aitv.it_value, &ctv);
                }
        } else {
                aitv = p->p_timer[uap->which];
        }
        crit_exit();
        rel_mplock();
        return (copyout(&aitv, uap->itv, sizeof (struct itimerval)));
}

/*
 * MPALMOSTSAFE
 */
int
sys_setitimer(struct setitimer_args *uap)
{
        struct itimerval aitv;
        struct timeval ctv;
        struct itimerval *itvp;
        struct proc *p = curproc;
        int 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 = sys_getitimer((struct getitimer_args *)uap)))
                return (error);
        if (itvp == 0)
                return (0);
        if (itimerfix(&aitv.it_value))
                return (EINVAL);
        if (!timevalisset(&aitv.it_value))
                timevalclear(&aitv.it_interval);
        else if (itimerfix(&aitv.it_interval))
                return (EINVAL);
        get_mplock();
        crit_enter();
        if (uap->which == ITIMER_REAL) {
                if (timevalisset(&p->p_realtimer.it_value))
                        callout_stop(&p->p_ithandle);
                if (timevalisset(&aitv.it_value)) 
                        callout_reset(&p->p_ithandle,
                            tvtohz_high(&aitv.it_value), realitexpire, p);
                getmicrouptime(&ctv);
                timevaladd(&aitv.it_value, &ctv);
                p->p_realtimer = aitv;
        } else {
                p->p_timer[uap->which] = aitv;
        }
        crit_exit();
        rel_mplock();
        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.
 * tvtohz_high() always adds 1 to allow for the time until the next clock
 * interrupt being strictly less than 1 clock tick, but we don't want
 * that here since we want to appear to be in sync with the clock
 * interrupt even when we're delayed.
 */
void
realitexpire(void *arg)
{
        struct proc *p;
        struct timeval ctv, ntv;

        p = (struct proc *)arg;
        ksignal(p, SIGALRM);
        if (!timevalisset(&p->p_realtimer.it_interval)) {
                timevalclear(&p->p_realtimer.it_value);
                return;
        }
        for (;;) {
                crit_enter();
                timevaladd(&p->p_realtimer.it_value,
                    &p->p_realtimer.it_interval);
                getmicrouptime(&ctv);
                if (timevalcmp(&p->p_realtimer.it_value, &ctv, >)) {
                        ntv = p->p_realtimer.it_value;
                        timevalsub(&ntv, &ctv);
                        callout_reset(&p->p_ithandle, tvtohz_low(&ntv),
                                      realitexpire, p);
                        crit_exit();
                        return;
                }
                crit_exit();
        }
}

/*
 * 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.)
 *
 * MPSAFE
 */
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 < ustick)
                tv->tv_usec = ustick;
        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
 * 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 (timevalisset(&itp->it_value))
                return (1);
        /* expired, exactly at end of interval */
expire:
        if (timevalisset(&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.
 */
void
timevaladd(struct timeval *t1, const struct timeval *t2)
{

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

void
timevalsub(struct timeval *t1, const struct timeval *t2)
{

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

static void
timevalfix(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;
        }
}

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

        getmicrouptime(&tv);            /* NB: 10ms precision */
        delta = tv;
        timevalsub(&delta, lasttime);

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

        return (rv);
}

/*
 * ppsratecheck(): packets (or events) per second limitation.
 *
 * Return 0 if the limit is to be enforced (e.g. the caller
 * should drop a packet because of the rate limitation).
 *
 * maxpps of 0 always causes zero to be returned.  maxpps of -1
 * always causes 1 to be returned; this effectively defeats rate
 * limiting.
 *
 * Note that we maintain the struct timeval for compatibility
 * with other bsd systems.  We reuse the storage and just monitor
 * clock ticks for minimal overhead.  
 */
int
ppsratecheck(struct timeval *lasttime, int *curpps, int maxpps)
{
        int now;

        /*
         * Reset the last time and counter if this is the first call
         * or more than a second has passed since the last update of
         * lasttime.
         */
        now = ticks;
        if (lasttime->tv_sec == 0 || (u_int)(now - lasttime->tv_sec) >= hz) {
                lasttime->tv_sec = now;
                *curpps = 1;
                return (maxpps != 0);
        } else {
                (*curpps)++;            /* NB: ignore potential overflow */
                return (maxpps < 0 || *curpps < maxpps);
        }
}