/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (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 2003 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright 2016, Joyent Inc.
 */

#include <sys/timer.h>
#include <sys/systm.h>
#include <sys/param.h>
#include <sys/kmem.h>
#include <sys/debug.h>
#include <sys/cyclic.h>
#include <sys/cmn_err.h>
#include <sys/pset.h>
#include <sys/atomic.h>
#include <sys/policy.h>

static clock_backend_t clock_highres;

/* minimum non-privileged interval (200us) */
long clock_highres_interval_min = 200000;

/*ARGSUSED*/
static int
clock_highres_settime(timespec_t *ts)
{
        return (EINVAL);
}

static int
clock_highres_gettime(timespec_t *ts)
{
        hrt2ts(gethrtime(), (timestruc_t *)ts);

        return (0);
}

static int
clock_highres_getres(timespec_t *ts)
{
        hrt2ts(cyclic_getres(), (timestruc_t *)ts);

        return (0);
}

/*ARGSUSED*/
static int
clock_highres_timer_create(itimer_t *it, void (*fire)(itimer_t *))
{
        it->it_arg = kmem_zalloc(sizeof (cyclic_id_t), KM_SLEEP);
        it->it_fire = fire;

        return (0);
}

static void
clock_highres_fire(void *arg)
{
        itimer_t *it = (itimer_t *)arg;
        hrtime_t *addr = &it->it_hrtime;
        hrtime_t old = *addr, new = gethrtime();

        do {
                old = *addr;
        } while (atomic_cas_64((uint64_t *)addr, old, new) != old);

        it->it_fire(it);
}

static int
clock_highres_timer_settime(itimer_t *it, int flags,
    const struct itimerspec *when)
{
        cyclic_id_t cyc, *cycp = it->it_arg;
        proc_t *p = curproc;
        kthread_t *t = curthread;
        cyc_time_t cyctime;
        cyc_handler_t hdlr;
        cpu_t *cpu;
        cpupart_t *cpupart;
        int pset;
        boolean_t value_need_clamp = B_FALSE;
        boolean_t intval_need_clamp = B_FALSE;
        cred_t *cr = CRED();
        struct itimerspec clamped;

        /*
         * CLOCK_HIGHRES timers of sufficiently high resolution can deny
         * service; only allow privileged users to create such timers.
         * Non-privileged users (those without the "proc_clock_highres"
         * privilege) can create timers with lower resolution but if they
         * attempt to use a very low time value (< 200us) then their
         * timer will be clamped at 200us.
         */
        if (when->it_value.tv_sec == 0 &&
            when->it_value.tv_nsec > 0 &&
            when->it_value.tv_nsec < clock_highres_interval_min)
                value_need_clamp = B_TRUE;

        if (when->it_interval.tv_sec == 0 &&
            when->it_interval.tv_nsec > 0 &&
            when->it_interval.tv_nsec < clock_highres_interval_min)
                intval_need_clamp = B_TRUE;

        if ((value_need_clamp || intval_need_clamp) &&
            secpolicy_clock_highres(cr) != 0) {
                clamped.it_value.tv_sec = when->it_value.tv_sec;
                clamped.it_interval.tv_sec = when->it_interval.tv_sec;

                if (value_need_clamp) {
                        clamped.it_value.tv_nsec = clock_highres_interval_min;
                } else {
                        clamped.it_value.tv_nsec = when->it_value.tv_nsec;
                }

                if (intval_need_clamp) {
                        clamped.it_interval.tv_nsec =
                            clock_highres_interval_min;
                } else {
                        clamped.it_interval.tv_nsec = when->it_interval.tv_nsec;
                }

                when = &clamped;
        }

        cyctime.cyt_when = ts2hrt(&when->it_value);
        cyctime.cyt_interval = ts2hrt(&when->it_interval);

        if (cyctime.cyt_when != 0 && cyctime.cyt_interval == 0 &&
            it->it_itime.it_interval.tv_sec == 0 &&
            it->it_itime.it_interval.tv_nsec == 0 &&
            (cyc = *cycp) != CYCLIC_NONE) {
                /*
                 * If our existing timer is a one-shot and our new timer is a
                 * one-shot, we'll save ourselves a world of grief and just
                 * reprogram the cyclic.
                 */
                it->it_itime = *when;

                if (!(flags & TIMER_ABSTIME))
                        cyctime.cyt_when += gethrtime();

                hrt2ts(cyctime.cyt_when, &it->it_itime.it_value);
                (void) cyclic_reprogram(cyc, cyctime.cyt_when);
                return (0);
        }

        mutex_enter(&cpu_lock);
        if ((cyc = *cycp) != CYCLIC_NONE) {
                cyclic_remove(cyc);
                *cycp = CYCLIC_NONE;
        }

        if (cyctime.cyt_when == 0) {
                mutex_exit(&cpu_lock);
                return (0);
        }

        if (!(flags & TIMER_ABSTIME))
                cyctime.cyt_when += gethrtime();

        /*
         * Now we will check for overflow (that is, we will check to see
         * that the start time plus the interval time doesn't exceed
         * INT64_MAX).  The astute code reviewer will observe that this
         * one-time check doesn't guarantee that a future expiration
         * will not wrap.  We wish to prove, then, that if a future
         * expiration does wrap, the earliest the problem can be encountered
         * is (INT64_MAX / 2) nanoseconds (191 years) after boot.  Formally:
         *
         *  Given:      s + i < m       s > 0   i > 0
         *              s + ni > m      n > 1
         *
         *    (where "s" is the start time, "i" is the interval, "n" is the
         *    number of times the cyclic has fired and "m" is INT64_MAX)
         *
         *  Prove:
         *              (a)  s + (n - 1)i > (m / 2)
         *              (b)  s + (n - 1)i < m
         *
         * That is, prove that we must have fired at least once 191 years
         * after boot.  The proof is very straightforward; since the left
         * side of (a) is minimized when i is small, it is sufficient to show
         * that the statement is true for i's smallest possible value
         * (((m - s) / n) + epsilon).  The same goes for (b); showing that the
         * statement is true for i's largest possible value (m - s + epsilon)
         * is sufficient to prove the statement.
         *
         * The actual arithmetic manipulation is left up to reader.
         */
        if (cyctime.cyt_when > INT64_MAX - cyctime.cyt_interval) {
                mutex_exit(&cpu_lock);
                return (EOVERFLOW);
        }

        if (cyctime.cyt_interval == 0) {
                /*
                 * If this is a one-shot, then we set the interval to be
                 * inifinite.  If this timer is never touched, this cyclic will
                 * simply consume space in the cyclic subsystem.  As soon as
                 * timer_settime() or timer_delete() is called, the cyclic is
                 * removed (so it's not possible to run the machine out
                 * of resources by creating one-shots).
                 */
                cyctime.cyt_interval = CY_INFINITY;
        }

        it->it_itime = *when;

        hrt2ts(cyctime.cyt_when, &it->it_itime.it_value);

        hdlr.cyh_func = (cyc_func_t)clock_highres_fire;
        hdlr.cyh_arg = it;
        hdlr.cyh_level = CY_LOW_LEVEL;

        if (cyctime.cyt_when != 0)
                *cycp = cyc = cyclic_add(&hdlr, &cyctime);

        /*
         * Now that we have the cyclic created, we need to bind it to our
         * bound CPU and processor set (if any).
         */
        mutex_enter(&p->p_lock);
        cpu = t->t_bound_cpu;
        cpupart = t->t_cpupart;
        pset = t->t_bind_pset;

        mutex_exit(&p->p_lock);

        cyclic_bind(cyc, cpu, pset == PS_NONE ? NULL : cpupart);

        mutex_exit(&cpu_lock);

        return (0);
}

static int
clock_highres_timer_gettime(itimer_t *it, struct itimerspec *when)
{
        /*
         * CLOCK_HIGHRES doesn't update it_itime.
         */
        hrtime_t start = ts2hrt(&it->it_itime.it_value);
        hrtime_t interval = ts2hrt(&it->it_itime.it_interval);
        hrtime_t diff, now = gethrtime();
        hrtime_t *addr = &it->it_hrtime;
        hrtime_t last;

        /*
         * We're using atomic_cas_64() here only to assure that we slurp the
         * entire timestamp atomically.
         */
        last = atomic_cas_64((uint64_t *)addr, 0, 0);

        *when = it->it_itime;

        if (!timerspecisset(&when->it_value))
                return (0);

        if (start > now) {
                /*
                 * We haven't gone off yet...
                 */
                diff = start - now;
        } else {
                if (interval == 0) {
                        /*
                         * This is a one-shot which should have already
                         * fired; set it_value to 0.
                         */
                        timerspecclear(&when->it_value);
                        return (0);
                }

                /*
                 * Calculate how far we are into this interval.
                 */
                diff = (now - start) % interval;

                /*
                 * Now check to see if we've dealt with the last interval
                 * yet.
                 */
                if (now - diff > last) {
                        /*
                         * The last interval hasn't fired; set it_value to 0.
                         */
                        timerspecclear(&when->it_value);
                        return (0);
                }

                /*
                 * The last interval _has_ fired; we can return the amount
                 * of time left in this interval.
                 */
                diff = interval - diff;
        }

        hrt2ts(diff, &when->it_value);

        return (0);
}

static int
clock_highres_timer_delete(itimer_t *it)
{
        cyclic_id_t cyc;

        if (it->it_arg == NULL) {
                /*
                 * This timer was never fully created; we must have failed
                 * in the clock_highres_timer_create() routine.
                 */
                return (0);
        }

        mutex_enter(&cpu_lock);

        if ((cyc = *((cyclic_id_t *)it->it_arg)) != CYCLIC_NONE)
                cyclic_remove(cyc);

        mutex_exit(&cpu_lock);

        kmem_free(it->it_arg, sizeof (cyclic_id_t));

        return (0);
}

static void
clock_highres_timer_lwpbind(itimer_t *it)
{
        proc_t *p = curproc;
        kthread_t *t = curthread;
        cyclic_id_t cyc = *((cyclic_id_t *)it->it_arg);
        cpu_t *cpu;
        cpupart_t *cpupart;
        int pset;

        if (cyc == CYCLIC_NONE)
                return;

        mutex_enter(&cpu_lock);
        mutex_enter(&p->p_lock);

        /*
         * Okay, now we can safely look at the bindings.
         */
        cpu = t->t_bound_cpu;
        cpupart = t->t_cpupart;
        pset = t->t_bind_pset;

        /*
         * Now we drop p_lock.  We haven't dropped cpu_lock; we're guaranteed
         * that even if the bindings change, the CPU and/or processor set
         * that this timer was bound to remain valid (and the combination
         * remains self-consistent).
         */
        mutex_exit(&p->p_lock);

        cyclic_bind(cyc, cpu, pset == PS_NONE ? NULL : cpupart);

        mutex_exit(&cpu_lock);
}

void
clock_highres_init()
{
        clock_backend_t *be = &clock_highres;
        struct sigevent *ev = &be->clk_default;

        ev->sigev_signo = SIGALRM;
        ev->sigev_notify = SIGEV_SIGNAL;
        ev->sigev_value.sival_ptr = NULL;

        be->clk_clock_settime = clock_highres_settime;
        be->clk_clock_gettime = clock_highres_gettime;
        be->clk_clock_getres = clock_highres_getres;
        be->clk_timer_create = clock_highres_timer_create;
        be->clk_timer_gettime = clock_highres_timer_gettime;
        be->clk_timer_settime = clock_highres_timer_settime;
        be->clk_timer_delete = clock_highres_timer_delete;
        be->clk_timer_lwpbind = clock_highres_timer_lwpbind;

        clock_add_backend(CLOCK_HIGHRES, &clock_highres);
}