8322 nl: misleading-indentation

[unleashed/tickless.git] / usr / src / uts / common / os / timer.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2012, Joyent, Inc. All rights reserved.
 */

#include <sys/timer.h>
#include <sys/systm.h>
#include <sys/param.h>
#include <sys/kmem.h>
#include <sys/debug.h>
#include <sys/policy.h>
#include <sys/port_impl.h>
#include <sys/port_kernel.h>
#include <sys/contract/process_impl.h>

static kmem_cache_t *clock_timer_cache;
static clock_backend_t *clock_backend[CLOCK_MAX];
static int timer_port_callback(void *, int *, pid_t, int, void *);
static void timer_close_port(void *, int, pid_t, int);

#define CLOCK_BACKEND(clk) \
        ((clk) < CLOCK_MAX && (clk) >= 0 ? clock_backend[(clk)] : NULL)

/*
 * Tunable to increase the maximum number of POSIX timers per-process.  This
 * may _only_ be tuned in /etc/system or by patching the kernel binary; it
 * _cannot_ be tuned on a running system.
 */
int timer_max = _TIMER_MAX;

/*
 * timer_lock() locks the specified interval timer.  It doesn't look at the
 * ITLK_REMOVE bit; it's up to callers to look at this if they need to
 * care.  p_lock must be held on entry; it may be dropped and reaquired,
 * but timer_lock() will always return with p_lock held.
 *
 * Note that timer_create() doesn't call timer_lock(); it creates timers
 * with the ITLK_LOCKED bit explictly set.
 */
static void
timer_lock(proc_t *p, itimer_t *it)
{
        ASSERT(MUTEX_HELD(&p->p_lock));

        while (it->it_lock & ITLK_LOCKED) {
                it->it_blockers++;
                cv_wait(&it->it_cv, &p->p_lock);
                it->it_blockers--;
        }

        it->it_lock |= ITLK_LOCKED;
}

/*
 * timer_unlock() unlocks the specified interval timer, waking up any
 * waiters.  p_lock must be held on entry; it will not be dropped by
 * timer_unlock().
 */
static void
timer_unlock(proc_t *p, itimer_t *it)
{
        ASSERT(MUTEX_HELD(&p->p_lock));
        ASSERT(it->it_lock & ITLK_LOCKED);
        it->it_lock &= ~ITLK_LOCKED;
        cv_signal(&it->it_cv);
}

/*
 * timer_delete_locked() takes a proc pointer, timer ID and locked interval
 * timer, and deletes the specified timer.  It must be called with p_lock
 * held, and cannot be called on a timer which already has ITLK_REMOVE set;
 * the caller must check this.  timer_delete_locked() will set the ITLK_REMOVE
 * bit and will iteratively unlock and lock the interval timer until all
 * blockers have seen the ITLK_REMOVE and cleared out.  It will then zero
 * out the specified entry in the p_itimer array, and call into the clock
 * backend to complete the deletion.
 *
 * This function will always return with p_lock held.
 */
static void
timer_delete_locked(proc_t *p, timer_t tid, itimer_t *it)
{
        ASSERT(MUTEX_HELD(&p->p_lock));
        ASSERT(!(it->it_lock & ITLK_REMOVE));
        ASSERT(it->it_lock & ITLK_LOCKED);

        it->it_lock |= ITLK_REMOVE;

        /*
         * If there are threads waiting to lock this timer, we'll unlock
         * the timer, and block on the cv.  Threads blocking our removal will
         * have the opportunity to run; when they see the ITLK_REMOVE flag
         * set, they will immediately unlock the timer.
         */
        while (it->it_blockers) {
                timer_unlock(p, it);
                cv_wait(&it->it_cv, &p->p_lock);
                timer_lock(p, it);
        }

        ASSERT(p->p_itimer[tid] == it);
        p->p_itimer[tid] = NULL;

        /*
         * No one is blocked on this timer, and no one will be (we've set
         * p_itimer[tid] to be NULL; no one can find it).  Now we call into
         * the clock backend to delete the timer; it is up to the backend to
         * guarantee that timer_fire() has completed (and will never again
         * be called) for this timer.
         */
        mutex_exit(&p->p_lock);

        it->it_backend->clk_timer_delete(it);

        if (it->it_portev) {
                mutex_enter(&it->it_mutex);
                if (it->it_portev) {
                        port_kevent_t   *pev;
                        /* dissociate timer from the event port */
                        (void) port_dissociate_ksource(it->it_portfd,
                            PORT_SOURCE_TIMER, (port_source_t *)it->it_portsrc);
                        pev = (port_kevent_t *)it->it_portev;
                        it->it_portev = NULL;
                        it->it_flags &= ~IT_PORT;
                        it->it_pending = 0;
                        mutex_exit(&it->it_mutex);
                        (void) port_remove_done_event(pev);
                        port_free_event(pev);
                } else {
                        mutex_exit(&it->it_mutex);
                }
        }

        mutex_enter(&p->p_lock);

        /*
         * We need to be careful freeing the sigqueue for this timer;
         * if a signal is pending, the sigqueue needs to be freed
         * synchronously in siginfofree().  The need to free the sigqueue
         * in siginfofree() is indicated by setting sq_func to NULL.
         */
        if (it->it_pending > 0) {
                it->it_sigq->sq_func = NULL;
        } else {
                kmem_free(it->it_sigq, sizeof (sigqueue_t));
        }

        ASSERT(it->it_blockers == 0);
        kmem_cache_free(clock_timer_cache, it);
}

/*
 * timer_grab() and its companion routine, timer_release(), are wrappers
 * around timer_lock()/_unlock() which allow the timer_*(3R) routines to
 * (a) share error handling code and (b) not grab p_lock themselves.  Routines
 * which are called with p_lock held (e.g. timer_lwpbind(), timer_lwpexit())
 * must call timer_lock()/_unlock() explictly.
 *
 * timer_grab() takes a proc and a timer ID, and returns a pointer to a
 * locked interval timer.  p_lock must _not_ be held on entry; timer_grab()
 * may acquire p_lock, but will always return with p_lock dropped.
 *
 * If timer_grab() fails, it will return NULL.  timer_grab() will fail if
 * one or more of the following is true:
 *
 *  (a) The specified timer ID is out of range.
 *
 *  (b) The specified timer ID does not correspond to a timer ID returned
 *      from timer_create(3R).
 *
 *  (c) The specified timer ID is currently being removed.
 *
 */
static itimer_t *
timer_grab(proc_t *p, timer_t tid)
{
        itimer_t **itp, *it;

        if (tid >= timer_max || tid < 0)
                return (NULL);

        mutex_enter(&p->p_lock);

        if ((itp = p->p_itimer) == NULL || (it = itp[tid]) == NULL) {
                mutex_exit(&p->p_lock);
                return (NULL);
        }

        timer_lock(p, it);

        if (it->it_lock & ITLK_REMOVE) {
                /*
                 * Someone is removing this timer; it will soon be invalid.
                 */
                timer_unlock(p, it);
                mutex_exit(&p->p_lock);
                return (NULL);
        }

        mutex_exit(&p->p_lock);

        return (it);
}

/*
 * timer_release() releases a timer acquired with timer_grab().  p_lock
 * should not be held on entry; timer_release() will acquire p_lock but
 * will drop it before returning.
 */
static void
timer_release(proc_t *p, itimer_t *it)
{
        mutex_enter(&p->p_lock);
        timer_unlock(p, it);
        mutex_exit(&p->p_lock);
}

/*
 * timer_delete_grabbed() deletes a timer acquired with timer_grab().
 * p_lock should not be held on entry; timer_delete_grabbed() will acquire
 * p_lock, but will drop it before returning.
 */
static void
timer_delete_grabbed(proc_t *p, timer_t tid, itimer_t *it)
{
        mutex_enter(&p->p_lock);
        timer_delete_locked(p, tid, it);
        mutex_exit(&p->p_lock);
}

void
clock_timer_init()
{
        clock_timer_cache = kmem_cache_create("timer_cache",
            sizeof (itimer_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
}

void
clock_add_backend(clockid_t clock, clock_backend_t *backend)
{
        ASSERT(clock >= 0 && clock < CLOCK_MAX);
        ASSERT(clock_backend[clock] == NULL);

        clock_backend[clock] = backend;
}

clock_backend_t *
clock_get_backend(clockid_t clock)
{
        if (clock < 0 || clock >= CLOCK_MAX)
                return (NULL);

        return (clock_backend[clock]);
}

int
clock_settime(clockid_t clock, timespec_t *tp)
{
        timespec_t t;
        clock_backend_t *backend;
        int error;

        if ((backend = CLOCK_BACKEND(clock)) == NULL)
                return (set_errno(EINVAL));

        if (secpolicy_settime(CRED()) != 0)
                return (set_errno(EPERM));

        if (get_udatamodel() == DATAMODEL_NATIVE) {
                if (copyin(tp, &t, sizeof (timespec_t)) != 0)
                        return (set_errno(EFAULT));
        } else {
                timespec32_t t32;

                if (copyin(tp, &t32, sizeof (timespec32_t)) != 0)
                        return (set_errno(EFAULT));

                TIMESPEC32_TO_TIMESPEC(&t, &t32);
        }

        if (itimerspecfix(&t))
                return (set_errno(EINVAL));

        error = backend->clk_clock_settime(&t);

        if (error)
                return (set_errno(error));

        return (0);
}

int
clock_gettime(clockid_t clock, timespec_t *tp)
{
        timespec_t t;
        clock_backend_t *backend;
        int error;

        if ((backend = CLOCK_BACKEND(clock)) == NULL)
                return (set_errno(EINVAL));

        error = backend->clk_clock_gettime(&t);

        if (error)
                return (set_errno(error));

        if (get_udatamodel() == DATAMODEL_NATIVE) {
                if (copyout(&t, tp, sizeof (timespec_t)) != 0)
                        return (set_errno(EFAULT));
        } else {
                timespec32_t t32;

                if (TIMESPEC_OVERFLOW(&t))
                        return (set_errno(EOVERFLOW));
                TIMESPEC_TO_TIMESPEC32(&t32, &t);

                if (copyout(&t32, tp, sizeof (timespec32_t)) != 0)
                        return (set_errno(EFAULT));
        }

        return (0);
}

int
clock_getres(clockid_t clock, timespec_t *tp)
{
        timespec_t t;
        clock_backend_t *backend;
        int error;

        /*
         * Strangely, the standard defines clock_getres() with a NULL tp
         * to do nothing (regardless of the validity of the specified
         * clock_id).  Go figure.
         */
        if (tp == NULL)
                return (0);

        if ((backend = CLOCK_BACKEND(clock)) == NULL)
                return (set_errno(EINVAL));

        error = backend->clk_clock_getres(&t);

        if (error)
                return (set_errno(error));

        if (get_udatamodel() == DATAMODEL_NATIVE) {
                if (copyout(&t, tp, sizeof (timespec_t)) != 0)
                        return (set_errno(EFAULT));
        } else {
                timespec32_t t32;

                if (TIMESPEC_OVERFLOW(&t))
                        return (set_errno(EOVERFLOW));
                TIMESPEC_TO_TIMESPEC32(&t32, &t);

                if (copyout(&t32, tp, sizeof (timespec32_t)) != 0)
                        return (set_errno(EFAULT));
        }

        return (0);
}

void
timer_signal(sigqueue_t *sigq)
{
        itimer_t *it = (itimer_t *)sigq->sq_backptr;

        /*
         * There are some conditions during a fork or an exit when we can
         * call siginfofree() without p_lock held.  To prevent a race
         * between timer_signal() and timer_fire() with regard to it_pending,
         * we therefore acquire it_mutex in both paths.
         */
        mutex_enter(&it->it_mutex);
        ASSERT(it->it_pending > 0);
        it->it_overrun = it->it_pending - 1;
        it->it_pending = 0;
        mutex_exit(&it->it_mutex);
}

/*
 * This routine is called from the clock backend.
 */
static void
timer_fire(itimer_t *it)
{
        proc_t *p;
        int proc_lock_held;

        if (it->it_flags & IT_SIGNAL) {
                /*
                 * See the comment in timer_signal() for why it is not
                 * sufficient to only grab p_lock here. Because p_lock can be
                 * held on entry to timer_signal(), the lock ordering is
                 * necessarily p_lock before it_mutex.
                 */

                p = it->it_proc;
                proc_lock_held = 1;
                mutex_enter(&p->p_lock);
        } else {
                /*
                 * IT_PORT:
                 * If a timer was ever programmed to send events to a port,
                 * the IT_PORT flag will remain set until:
                 * a) the timer is deleted (see timer_delete_locked()) or
                 * b) the port is being closed (see timer_close_port()).
                 * Both cases are synchronized with the it_mutex.
                 * We don't need to use the p_lock because it is only
                 * required in the IT_SIGNAL case.
                 * If IT_PORT was set and the port is being closed then
                 * the timer notification is set to NONE. In such a case
                 * the timer itself and the it_pending counter remain active
                 * until the application deletes the counter or the process
                 * exits.
                 */
                proc_lock_held = 0;
        }
        mutex_enter(&it->it_mutex);

        if (it->it_pending > 0) {
                if (it->it_pending < INT_MAX)
                        it->it_pending++;
                mutex_exit(&it->it_mutex);
        } else {
                if (it->it_flags & IT_PORT) {
                        it->it_pending = 1;
                        port_send_event((port_kevent_t *)it->it_portev);
                        mutex_exit(&it->it_mutex);
                } else if (it->it_flags & IT_SIGNAL) {
                        it->it_pending = 1;
                        mutex_exit(&it->it_mutex);
                        sigaddqa(p, NULL, it->it_sigq);
                } else {
                        mutex_exit(&it->it_mutex);
                }
        }

        if (proc_lock_held)
                mutex_exit(&p->p_lock);
}

int
timer_create(clockid_t clock, struct sigevent *evp, timer_t *tid)
{
        struct sigevent ev;
        proc_t *p = curproc;
        clock_backend_t *backend;
        itimer_t *it, **itp;
        sigqueue_t *sigq;
        cred_t *cr = CRED();
        int error = 0;
        timer_t i;
        port_notify_t tim_pnevp;
        port_kevent_t *pkevp = NULL;

        if ((backend = CLOCK_BACKEND(clock)) == NULL)
                return (set_errno(EINVAL));

        if (evp != NULL) {
                /*
                 * short copyin() for binary compatibility
                 * fetch oldsigevent to determine how much to copy in.
                 */
                if (get_udatamodel() == DATAMODEL_NATIVE) {
                        if (copyin(evp, &ev, sizeof (struct oldsigevent)))
                                return (set_errno(EFAULT));

                        if (ev.sigev_notify == SIGEV_PORT ||
                            ev.sigev_notify == SIGEV_THREAD) {
                                if (copyin(ev.sigev_value.sival_ptr, &tim_pnevp,
                                    sizeof (port_notify_t)))
                                        return (set_errno(EFAULT));
                        }
#ifdef  _SYSCALL32_IMPL
                } else {
                        struct sigevent32 ev32;
                        port_notify32_t tim_pnevp32;

                        if (copyin(evp, &ev32, sizeof (struct oldsigevent32)))
                                return (set_errno(EFAULT));
                        ev.sigev_notify = ev32.sigev_notify;
                        ev.sigev_signo = ev32.sigev_signo;
                        /*
                         * See comment in sigqueue32() on handling of 32-bit
                         * sigvals in a 64-bit kernel.
                         */
                        ev.sigev_value.sival_int = ev32.sigev_value.sival_int;
                        if (ev.sigev_notify == SIGEV_PORT ||
                            ev.sigev_notify == SIGEV_THREAD) {
                                if (copyin((void *)(uintptr_t)
                                    ev32.sigev_value.sival_ptr,
                                    (void *)&tim_pnevp32,
                                    sizeof (port_notify32_t)))
                                        return (set_errno(EFAULT));
                                tim_pnevp.portnfy_port =
                                    tim_pnevp32.portnfy_port;
                                tim_pnevp.portnfy_user =
                                    (void *)(uintptr_t)tim_pnevp32.portnfy_user;
                        }
#endif
                }
                switch (ev.sigev_notify) {
                case SIGEV_NONE:
                        break;
                case SIGEV_SIGNAL:
                        if (ev.sigev_signo < 1 || ev.sigev_signo >= NSIG)
                                return (set_errno(EINVAL));
                        break;
                case SIGEV_THREAD:
                case SIGEV_PORT:
                        break;
                default:
                        return (set_errno(EINVAL));
                }
        } else {
                /*
                 * Use the clock's default sigevent (this is a structure copy).
                 */
                ev = backend->clk_default;
        }

        /*
         * We'll allocate our timer and sigqueue now, before we grab p_lock.
         * If we can't find an empty slot, we'll free them before returning.
         */
        it = kmem_cache_alloc(clock_timer_cache, KM_SLEEP);
        bzero(it, sizeof (itimer_t));
        mutex_init(&it->it_mutex, NULL, MUTEX_DEFAULT, NULL);
        sigq = kmem_zalloc(sizeof (sigqueue_t), KM_SLEEP);

        mutex_enter(&p->p_lock);

        /*
         * If this is this process' first timer, we need to attempt to allocate
         * an array of timerstr_t pointers.  We drop p_lock to perform the
         * allocation; if we return to discover that p_itimer is non-NULL,
         * we will free our allocation and drive on.
         */
        if ((itp = p->p_itimer) == NULL) {
                mutex_exit(&p->p_lock);
                itp = kmem_zalloc(timer_max * sizeof (itimer_t *), KM_SLEEP);
                mutex_enter(&p->p_lock);

                if (p->p_itimer == NULL)
                        p->p_itimer = itp;
                else {
                        kmem_free(itp, timer_max * sizeof (itimer_t *));
                        itp = p->p_itimer;
                }
        }

        for (i = 0; i < timer_max && itp[i] != NULL; i++)
                continue;

        if (i == timer_max) {
                /*
                 * We couldn't find a slot.  Drop p_lock, free the preallocated
                 * timer and sigqueue, and return an error.
                 */
                mutex_exit(&p->p_lock);
                kmem_cache_free(clock_timer_cache, it);
                kmem_free(sigq, sizeof (sigqueue_t));

                return (set_errno(EAGAIN));
        }

        ASSERT(i < timer_max && itp[i] == NULL);

        /*
         * If we develop other notification mechanisms, this will need
         * to call into (yet another) backend.
         */
        sigq->sq_info.si_signo = ev.sigev_signo;
        if (evp == NULL)
                sigq->sq_info.si_value.sival_int = i;
        else
                sigq->sq_info.si_value = ev.sigev_value;
        sigq->sq_info.si_code = SI_TIMER;
        sigq->sq_info.si_pid = p->p_pid;
        sigq->sq_info.si_ctid = PRCTID(p);
        sigq->sq_info.si_zoneid = getzoneid();
        sigq->sq_info.si_uid = crgetruid(cr);
        sigq->sq_func = timer_signal;
        sigq->sq_next = NULL;
        sigq->sq_backptr = it;
        it->it_sigq = sigq;
        it->it_backend = backend;
        it->it_lock = ITLK_LOCKED;
        itp[i] = it;


        if (ev.sigev_notify == SIGEV_THREAD ||
            ev.sigev_notify == SIGEV_PORT) {
                int port;

                /*
                 * This timer is programmed to use event port notification when
                 * the timer fires:
                 * - allocate a port event structure and prepare it to be sent
                 *   to the port as soon as the timer fires.
                 * - when the timer fires :
                 *   - if event structure was already sent to the port then this
                 *      is a timer fire overflow => increment overflow counter.
                 *   - otherwise send pre-allocated event structure to the port.
                 * - the events field of the port_event_t structure counts the
                 *   number of timer fired events.
                 * - The event structured is allocated using the
                 *   PORT_ALLOC_CACHED flag.
                 *   This flag indicates that the timer itself will manage and
                 *   free the event structure when required.
                 */

                it->it_flags |= IT_PORT;
                port = tim_pnevp.portnfy_port;

                /* associate timer as event source with the port */
                error = port_associate_ksource(port, PORT_SOURCE_TIMER,
                    (port_source_t **)&it->it_portsrc, timer_close_port,
                    (void *)it, NULL);
                if (error) {
                        itp[i] = NULL;          /* clear slot */
                        mutex_exit(&p->p_lock);
                        kmem_cache_free(clock_timer_cache, it);
                        kmem_free(sigq, sizeof (sigqueue_t));
                        return (set_errno(error));
                }

                /* allocate an event structure/slot */
                error = port_alloc_event(port, PORT_ALLOC_SCACHED,
                    PORT_SOURCE_TIMER, &pkevp);
                if (error) {
                        (void) port_dissociate_ksource(port, PORT_SOURCE_TIMER,
                            (port_source_t *)it->it_portsrc);
                        itp[i] = NULL;          /* clear slot */
                        mutex_exit(&p->p_lock);
                        kmem_cache_free(clock_timer_cache, it);
                        kmem_free(sigq, sizeof (sigqueue_t));
                        return (set_errno(error));
                }

                /* initialize event data */
                port_init_event(pkevp, i, tim_pnevp.portnfy_user,
                    timer_port_callback, it);
                it->it_portev = pkevp;
                it->it_portfd = port;
        } else {
                if (ev.sigev_notify == SIGEV_SIGNAL)
                        it->it_flags |= IT_SIGNAL;
        }

        mutex_exit(&p->p_lock);

        /*
         * Call on the backend to verify the event argument (or return
         * EINVAL if this clock type does not support timers).
         */
        if ((error = backend->clk_timer_create(it, timer_fire)) != 0)
                goto err;

        it->it_lwp = ttolwp(curthread);
        it->it_proc = p;

        if (copyout(&i, tid, sizeof (timer_t)) != 0) {
                error = EFAULT;
                goto err;
        }

        /*
         * If we're here, then we have successfully created the timer; we
         * just need to release the timer and return.
         */
        timer_release(p, it);

        return (0);

err:
        /*
         * If we're here, an error has occurred late in the timer creation
         * process.  We need to regrab p_lock, and delete the incipient timer.
         * Since we never unlocked the timer (it was born locked), it's
         * impossible for a removal to be pending.
         */
        ASSERT(!(it->it_lock & ITLK_REMOVE));
        timer_delete_grabbed(p, i, it);

        return (set_errno(error));
}

int
timer_gettime(timer_t tid, itimerspec_t *val)
{
        proc_t *p = curproc;
        itimer_t *it;
        itimerspec_t when;
        int error;

        if ((it = timer_grab(p, tid)) == NULL)
                return (set_errno(EINVAL));

        error = it->it_backend->clk_timer_gettime(it, &when);

        timer_release(p, it);

        if (error == 0) {
                if (get_udatamodel() == DATAMODEL_NATIVE) {
                        if (copyout(&when, val, sizeof (itimerspec_t)))
                                error = EFAULT;
                } else {
                        if (ITIMERSPEC_OVERFLOW(&when))
                                error = EOVERFLOW;
                        else {
                                itimerspec32_t w32;

                                ITIMERSPEC_TO_ITIMERSPEC32(&w32, &when)
                                if (copyout(&w32, val, sizeof (itimerspec32_t)))
                                        error = EFAULT;
                        }
                }
        }

        return (error ? set_errno(error) : 0);
}

int
timer_settime(timer_t tid, int flags, itimerspec_t *val, itimerspec_t *oval)
{
        itimerspec_t when;
        itimer_t *it;
        proc_t *p = curproc;
        int error;

        if (oval != NULL) {
                if ((error = timer_gettime(tid, oval)) != 0)
                        return (error);
        }

        if (get_udatamodel() == DATAMODEL_NATIVE) {
                if (copyin(val, &when, sizeof (itimerspec_t)))
                        return (set_errno(EFAULT));
        } else {
                itimerspec32_t w32;

                if (copyin(val, &w32, sizeof (itimerspec32_t)))
                        return (set_errno(EFAULT));

                ITIMERSPEC32_TO_ITIMERSPEC(&when, &w32);
        }

        if (itimerspecfix(&when.it_value) ||
            (itimerspecfix(&when.it_interval) &&
            timerspecisset(&when.it_value))) {
                return (set_errno(EINVAL));
        }

        if ((it = timer_grab(p, tid)) == NULL)
                return (set_errno(EINVAL));

        error = it->it_backend->clk_timer_settime(it, flags, &when);

        timer_release(p, it);

        return (error ? set_errno(error) : 0);
}

int
timer_delete(timer_t tid)
{
        proc_t *p = curproc;
        itimer_t *it;

        if ((it = timer_grab(p, tid)) == NULL)
                return (set_errno(EINVAL));

        timer_delete_grabbed(p, tid, it);

        return (0);
}

int
timer_getoverrun(timer_t tid)
{
        int overrun;
        proc_t *p = curproc;
        itimer_t *it;

        if ((it = timer_grab(p, tid)) == NULL)
                return (set_errno(EINVAL));

        /*
         * The it_overrun field is protected by p_lock; we need to acquire
         * it before looking at the value.
         */
        mutex_enter(&p->p_lock);
        overrun = it->it_overrun;
        mutex_exit(&p->p_lock);

        timer_release(p, it);

        return (overrun);
}

/*
 * Entered/exited with p_lock held, but will repeatedly drop and regrab p_lock.
 */
void
timer_lwpexit(void)
{
        timer_t i;
        proc_t *p = curproc;
        klwp_t *lwp = ttolwp(curthread);
        itimer_t *it, **itp;

        ASSERT(MUTEX_HELD(&p->p_lock));

        if ((itp = p->p_itimer) == NULL)
                return;

        for (i = 0; i < timer_max; i++) {
                if ((it = itp[i]) == NULL)
                        continue;

                timer_lock(p, it);

                if ((it->it_lock & ITLK_REMOVE) || it->it_lwp != lwp) {
                        /*
                         * This timer is either being removed or it isn't
                         * associated with this lwp.
                         */
                        timer_unlock(p, it);
                        continue;
                }

                /*
                 * The LWP that created this timer is going away.  To the user,
                 * our behavior here is explicitly undefined.  We will simply
                 * null out the it_lwp field; if the LWP was bound to a CPU,
                 * the cyclic will stay bound to that CPU until the process
                 * exits.
                 */
                it->it_lwp = NULL;
                timer_unlock(p, it);
        }
}

/*
 * Called to notify of an LWP binding change.  Entered/exited with p_lock
 * held, but will repeatedly drop and regrab p_lock.
 */
void
timer_lwpbind()
{
        timer_t i;
        proc_t *p = curproc;
        klwp_t *lwp = ttolwp(curthread);
        itimer_t *it, **itp;

        ASSERT(MUTEX_HELD(&p->p_lock));

        if ((itp = p->p_itimer) == NULL)
                return;

        for (i = 0; i < timer_max; i++) {
                if ((it = itp[i]) == NULL)
                        continue;

                timer_lock(p, it);

                if (!(it->it_lock & ITLK_REMOVE) && it->it_lwp == lwp) {
                        /*
                         * Drop p_lock and jump into the backend.
                         */
                        mutex_exit(&p->p_lock);
                        it->it_backend->clk_timer_lwpbind(it);
                        mutex_enter(&p->p_lock);
                }

                timer_unlock(p, it);
        }
}

/*
 * This function should only be called if p_itimer is non-NULL.
 */
void
timer_exit(void)
{
        timer_t i;
        proc_t *p = curproc;

        ASSERT(p->p_itimer != NULL);

        for (i = 0; i < timer_max; i++)
                (void) timer_delete(i);

        kmem_free(p->p_itimer, timer_max * sizeof (itimer_t *));
        p->p_itimer = NULL;
}

/*
 * timer_port_callback() is a callback function which is associated with the
 * timer event and is activated just before the event is delivered to the user.
 * The timer uses this function to update/set the overflow counter and
 * to reenable the use of the event structure.
 */

/* ARGSUSED */
static int
timer_port_callback(void *arg, int *events, pid_t pid, int flag, void *evp)
{
        itimer_t        *it = arg;

        mutex_enter(&it->it_mutex);
        if (curproc != it->it_proc) {
                /* can not deliver timer events to another proc */
                mutex_exit(&it->it_mutex);
                return (EACCES);
        }
        *events = it->it_pending;       /* 1 = 1 event, >1 # of overflows */
        it->it_pending = 0;             /* reinit overflow counter      */
        /*
         * This function can also be activated when the port is being closed
         * and a timer event is already submitted to the port.
         * In such a case the event port framework will use the
         * close-callback function to notify the events sources.
         * The timer close-callback function is timer_close_port() which
         * will free all allocated resources (including the allocated
         * port event structure).
         * For that reason we don't need to check the value of flag here.
         */
        mutex_exit(&it->it_mutex);
        return (0);
}

/*
 * port is being closed ... free all allocated port event structures
 * The delivered arg currently correspond to the first timer associated with
 * the port and it is not useable in this case.
 * We have to scan the list of activated timers in the current proc and
 * compare them with the delivered port id.
 */

/* ARGSUSED */
static void
timer_close_port(void *arg, int port, pid_t pid, int lastclose)
{
        proc_t          *p = curproc;
        timer_t         tid;
        itimer_t        *it;

        for (tid = 0; tid < timer_max; tid++) {
                if ((it = timer_grab(p, tid)) == NULL)
                        continue;
                if (it->it_portev) {
                        mutex_enter(&it->it_mutex);
                        if (it->it_portfd == port) {
                                port_kevent_t *pev;
                                pev = (port_kevent_t *)it->it_portev;
                                it->it_portev = NULL;
                                it->it_flags &= ~IT_PORT;
                                mutex_exit(&it->it_mutex);
                                (void) port_remove_done_event(pev);
                                port_free_event(pev);
                        } else {
                                mutex_exit(&it->it_mutex);
                        }
                }
                timer_release(p, it);
        }
}