/*
 * linux/kernel/posix-timers.c
 *
 *
 * 2002-10-15  Posix Clocks & timers
 *                           by George Anzinger george@mvista.com
 *
 *                           Copyright (C) 2002 2003 by MontaVista Software.
 *
 * 2004-06-01  Fix CLOCK_REALTIME clock/timer TIMER_ABSTIME bug.
 *                           Copyright (C) 2004 Boris Hu
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * MontaVista Software | 1237 East Arques Avenue | Sunnyvale | CA 94085 | USA
 */

/* These are all the functions necessary to implement
 * POSIX clocks & timers
 */
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/mutex.h>

#include <asm/uaccess.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/posix-clock.h>
#include <linux/posix-timers.h>
#include <linux/syscalls.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <linux/export.h>
#include <linux/hashtable.h>

/*
 * Management arrays for POSIX timers. Timers are now kept in static hash table
 * with 512 entries.
 * Timer ids are allocated by local routine, which selects proper hash head by
 * key, constructed from current->signal address and per signal struct counter.
 * This keeps timer ids unique per process, but now they can intersect between
 * processes.
 */

/*
 * Lets keep our timers in a slab cache :-)
 */
static struct kmem_cache *posix_timers_cache;

static DEFINE_HASHTABLE(posix_timers_hashtable, 9);
static DEFINE_SPINLOCK(hash_lock);

/*
 * we assume that the new SIGEV_THREAD_ID shares no bits with the other
 * SIGEV values.  Here we put out an error if this assumption fails.
 */
#if SIGEV_THREAD_ID != (SIGEV_THREAD_ID & \
                       ~(SIGEV_SIGNAL | SIGEV_NONE | SIGEV_THREAD))
#error "SIGEV_THREAD_ID must not share bit with other SIGEV values!"
#endif

/*
 * parisc wants ENOTSUP instead of EOPNOTSUPP
 */
#ifndef ENOTSUP
# define ENANOSLEEP_NOTSUP EOPNOTSUPP
#else
# define ENANOSLEEP_NOTSUP ENOTSUP
#endif

/*
 * The timer ID is turned into a timer address by idr_find().
 * Verifying a valid ID consists of:
 *
 * a) checking that idr_find() returns other than -1.
 * b) checking that the timer id matches the one in the timer itself.
 * c) that the timer owner is in the callers thread group.
 */

/*
 * CLOCKs: The POSIX standard calls for a couple of clocks and allows us
 *          to implement others.  This structure defines the various
 *          clocks.
 *
 * RESOLUTION: Clock resolution is used to round up timer and interval
 *          times, NOT to report clock times, which are reported with as
 *          much resolution as the system can muster.  In some cases this
 *          resolution may depend on the underlying clock hardware and
 *          may not be quantifiable until run time, and only then is the
 *          necessary code is written.  The standard says we should say
 *          something about this issue in the documentation...
 *
 * FUNCTIONS: The CLOCKs structure defines possible functions to
 *          handle various clock functions.
 *
 *          The standard POSIX timer management code assumes the
 *          following: 1.) The k_itimer struct (sched.h) is used for
 *          the timer.  2.) The list, it_lock, it_clock, it_id and
 *          it_pid fields are not modified by timer code.
 *
 * Permissions: It is assumed that the clock_settime() function defined
 *          for each clock will take care of permission checks.  Some
 *          clocks may be set able by any user (i.e. local process
 *          clocks) others not.  Currently the only set able clock we
 *          have is CLOCK_REALTIME and its high res counter part, both of
 *          which we beg off on and pass to do_sys_settimeofday().
 */

static struct k_clock posix_clocks[MAX_CLOCKS];

/*
 * These ones are defined below.
 */
static int common_nsleep(const clockid_t, int flags, struct timespec *t,
                         struct timespec __user *rmtp);
static int common_timer_create(struct k_itimer *new_timer);
static void common_timer_get(struct k_itimer *, struct itimerspec *);
static int common_timer_set(struct k_itimer *, int,
                            struct itimerspec *, struct itimerspec *);
static int common_timer_del(struct k_itimer *timer);

static enum hrtimer_restart posix_timer_fn(struct hrtimer *data);

static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags);

#define lock_timer(tid, flags)                                             \
({      struct k_itimer *__timr;                                           \
        __cond_lock(&__timr->it_lock, __timr = __lock_timer(tid, flags));  \
        __timr;                                                            \
})

static int hash(struct signal_struct *sig, unsigned int nr)
{
        return hash_32(hash32_ptr(sig) ^ nr, HASH_BITS(posix_timers_hashtable));
}

static struct k_itimer *__posix_timers_find(struct hlist_head *head,
                                            struct signal_struct *sig,
                                            timer_t id)
{
        struct k_itimer *timer;

        hlist_for_each_entry_rcu(timer, head, t_hash) {
                if ((timer->it_signal == sig) && (timer->it_id == id))
                        return timer;
        }
        return NULL;
}

static struct k_itimer *posix_timer_by_id(timer_t id)
{
        struct signal_struct *sig = current->signal;
        struct hlist_head *head = &posix_timers_hashtable[hash(sig, id)];

        return __posix_timers_find(head, sig, id);
}

static int posix_timer_add(struct k_itimer *timer)
{
        struct signal_struct *sig = current->signal;
        int first_free_id = sig->posix_timer_id;
        struct hlist_head *head;
        int ret = -ENOENT;

        do {
                spin_lock(&hash_lock);
                head = &posix_timers_hashtable[hash(sig, sig->posix_timer_id)];
                if (!__posix_timers_find(head, sig, sig->posix_timer_id)) {
                        hlist_add_head_rcu(&timer->t_hash, head);
                        ret = sig->posix_timer_id;
                }
                if (++sig->posix_timer_id < 0)
                        sig->posix_timer_id = 0;
                if ((sig->posix_timer_id == first_free_id) && (ret == -ENOENT))
                        /* Loop over all possible ids completed */
                        ret = -EAGAIN;
                spin_unlock(&hash_lock);
        } while (ret == -ENOENT);
        return ret;
}

static inline void unlock_timer(struct k_itimer *timr, unsigned long flags)
{
        spin_unlock_irqrestore(&timr->it_lock, flags);
}

/* Get clock_realtime */
static int posix_clock_realtime_get(clockid_t which_clock, struct timespec *tp)
{
        ktime_get_real_ts(tp);
        return 0;
}

/* Set clock_realtime */
static int posix_clock_realtime_set(const clockid_t which_clock,
                                    const struct timespec *tp)
{
        return do_sys_settimeofday(tp, NULL);
}

static int posix_clock_realtime_adj(const clockid_t which_clock,
                                    struct timex *t)
{
        return do_adjtimex(t);
}

/*
 * Get monotonic time for posix timers
 */
static int posix_ktime_get_ts(clockid_t which_clock, struct timespec *tp)
{
        ktime_get_ts(tp);
        return 0;
}

/*
 * Get monotonic-raw time for posix timers
 */
static int posix_get_monotonic_raw(clockid_t which_clock, struct timespec *tp)
{
        getrawmonotonic(tp);
        return 0;
}


static int posix_get_realtime_coarse(clockid_t which_clock, struct timespec *tp)
{
        *tp = current_kernel_time();
        return 0;
}

static int posix_get_monotonic_coarse(clockid_t which_clock,
                                                struct timespec *tp)
{
        *tp = get_monotonic_coarse();
        return 0;
}

static int posix_get_coarse_res(const clockid_t which_clock, struct timespec *tp)
{
        *tp = ktime_to_timespec(KTIME_LOW_RES);
        return 0;
}

static int posix_get_boottime(const clockid_t which_clock, struct timespec *tp)
{
        get_monotonic_boottime(tp);
        return 0;
}

static int posix_get_tai(clockid_t which_clock, struct timespec *tp)
{
        timekeeping_clocktai(tp);
        return 0;
}

/*
 * Initialize everything, well, just everything in Posix clocks/timers ;)
 */
static __init int init_posix_timers(void)
{
        struct k_clock clock_realtime = {
                .clock_getres   = hrtimer_get_res,
                .clock_get      = posix_clock_realtime_get,
                .clock_set      = posix_clock_realtime_set,
                .clock_adj      = posix_clock_realtime_adj,
                .nsleep         = common_nsleep,
                .nsleep_restart = hrtimer_nanosleep_restart,
                .timer_create   = common_timer_create,
                .timer_set      = common_timer_set,
                .timer_get      = common_timer_get,
                .timer_del      = common_timer_del,
        };
        struct k_clock clock_monotonic = {
                .clock_getres   = hrtimer_get_res,
                .clock_get      = posix_ktime_get_ts,
                .nsleep         = common_nsleep,
                .nsleep_restart = hrtimer_nanosleep_restart,
                .timer_create   = common_timer_create,
                .timer_set      = common_timer_set,
                .timer_get      = common_timer_get,
                .timer_del      = common_timer_del,
        };
        struct k_clock clock_monotonic_raw = {
                .clock_getres   = hrtimer_get_res,
                .clock_get      = posix_get_monotonic_raw,
        };
        struct k_clock clock_realtime_coarse = {
                .clock_getres   = posix_get_coarse_res,
                .clock_get      = posix_get_realtime_coarse,
        };
        struct k_clock clock_monotonic_coarse = {
                .clock_getres   = posix_get_coarse_res,
                .clock_get      = posix_get_monotonic_coarse,
        };
        struct k_clock clock_tai = {
                .clock_getres   = hrtimer_get_res,
                .clock_get      = posix_get_tai,
                .nsleep         = common_nsleep,
                .nsleep_restart = hrtimer_nanosleep_restart,
                .timer_create   = common_timer_create,
                .timer_set      = common_timer_set,
                .timer_get      = common_timer_get,
                .timer_del      = common_timer_del,
        };
        struct k_clock clock_boottime = {
                .clock_getres   = hrtimer_get_res,
                .clock_get      = posix_get_boottime,
                .nsleep         = common_nsleep,
                .nsleep_restart = hrtimer_nanosleep_restart,
                .timer_create   = common_timer_create,
                .timer_set      = common_timer_set,
                .timer_get      = common_timer_get,
                .timer_del      = common_timer_del,
        };

        posix_timers_register_clock(CLOCK_REALTIME, &clock_realtime);
        posix_timers_register_clock(CLOCK_MONOTONIC, &clock_monotonic);
        posix_timers_register_clock(CLOCK_MONOTONIC_RAW, &clock_monotonic_raw);
        posix_timers_register_clock(CLOCK_REALTIME_COARSE, &clock_realtime_coarse);
        posix_timers_register_clock(CLOCK_MONOTONIC_COARSE, &clock_monotonic_coarse);
        posix_timers_register_clock(CLOCK_BOOTTIME, &clock_boottime);
        posix_timers_register_clock(CLOCK_TAI, &clock_tai);

        posix_timers_cache = kmem_cache_create("posix_timers_cache",
                                        sizeof (struct k_itimer), 0, SLAB_PANIC,
                                        NULL);
        return 0;
}

__initcall(init_posix_timers);

static void schedule_next_timer(struct k_itimer *timr)
{
        struct hrtimer *timer = &timr->it.real.timer;

        if (timr->it.real.interval.tv64 == 0)
                return;

        timr->it_overrun += (unsigned int) hrtimer_forward(timer,
                                                timer->base->get_time(),
                                                timr->it.real.interval);

        timr->it_overrun_last = timr->it_overrun;
        timr->it_overrun = -1;
        ++timr->it_requeue_pending;
        hrtimer_restart(timer);
}

/*
 * This function is exported for use by the signal deliver code.  It is
 * called just prior to the info block being released and passes that
 * block to us.  It's function is to update the overrun entry AND to
 * restart the timer.  It should only be called if the timer is to be
 * restarted (i.e. we have flagged this in the sys_private entry of the
 * info block).
 *
 * To protect against the timer going away while the interrupt is queued,
 * we require that the it_requeue_pending flag be set.
 */
void do_schedule_next_timer(struct siginfo *info)
{
        struct k_itimer *timr;
        unsigned long flags;

        timr = lock_timer(info->si_tid, &flags);

        if (timr && timr->it_requeue_pending == info->si_sys_private) {
                if (timr->it_clock < 0)
                        posix_cpu_timer_schedule(timr);
                else
                        schedule_next_timer(timr);

                info->si_overrun += timr->it_overrun_last;
        }

        if (timr)
                unlock_timer(timr, flags);
}

int posix_timer_event(struct k_itimer *timr, int si_private)
{
        struct task_struct *task;
        int shared, ret = -1;
        /*
         * FIXME: if ->sigq is queued we can race with
         * dequeue_signal()->do_schedule_next_timer().
         *
         * If dequeue_signal() sees the "right" value of
         * si_sys_private it calls do_schedule_next_timer().
         * We re-queue ->sigq and drop ->it_lock().
         * do_schedule_next_timer() locks the timer
         * and re-schedules it while ->sigq is pending.
         * Not really bad, but not that we want.
         */
        timr->sigq->info.si_sys_private = si_private;

        rcu_read_lock();
        task = pid_task(timr->it_pid, PIDTYPE_PID);
        if (task) {
                shared = !(timr->it_sigev_notify & SIGEV_THREAD_ID);
                ret = send_sigqueue(timr->sigq, task, shared);
        }
        rcu_read_unlock();
        /* If we failed to send the signal the timer stops. */
        return ret > 0;
}
EXPORT_SYMBOL_GPL(posix_timer_event);

/*
 * This function gets called when a POSIX.1b interval timer expires.  It
 * is used as a callback from the kernel internal timer.  The
 * run_timer_list code ALWAYS calls with interrupts on.

 * This code is for CLOCK_REALTIME* and CLOCK_MONOTONIC* timers.
 */
static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
{
        struct k_itimer *timr;
        unsigned long flags;
        int si_private = 0;
        enum hrtimer_restart ret = HRTIMER_NORESTART;

        timr = container_of(timer, struct k_itimer, it.real.timer);
        spin_lock_irqsave(&timr->it_lock, flags);

        if (timr->it.real.interval.tv64 != 0)
                si_private = ++timr->it_requeue_pending;

        if (posix_timer_event(timr, si_private)) {
                /*
                 * signal was not sent because of sig_ignor
                 * we will not get a call back to restart it AND
                 * it should be restarted.
                 */
                if (timr->it.real.interval.tv64 != 0) {
                        ktime_t now = hrtimer_cb_get_time(timer);

                        /*
                         * FIXME: What we really want, is to stop this
                         * timer completely and restart it in case the
                         * SIG_IGN is removed. This is a non trivial
                         * change which involves sighand locking
                         * (sigh !), which we don't want to do late in
                         * the release cycle.
                         *
                         * For now we just let timers with an interval
                         * less than a jiffie expire every jiffie to
                         * avoid softirq starvation in case of SIG_IGN
                         * and a very small interval, which would put
                         * the timer right back on the softirq pending
                         * list. By moving now ahead of time we trick
                         * hrtimer_forward() to expire the timer
                         * later, while we still maintain the overrun
                         * accuracy, but have some inconsistency in
                         * the timer_gettime() case. This is at least
                         * better than a starved softirq. A more
                         * complex fix which solves also another related
                         * inconsistency is already in the pipeline.
                         */
#ifdef CONFIG_HIGH_RES_TIMERS
                        {
                                ktime_t kj = ktime_set(0, NSEC_PER_SEC / HZ);

                                if (timr->it.real.interval.tv64 < kj.tv64)
                                        now = ktime_add(now, kj);
                        }
#endif
                        timr->it_overrun += (unsigned int)
                                hrtimer_forward(timer, now,
                                                timr->it.real.interval);
                        ret = HRTIMER_RESTART;
                        ++timr->it_requeue_pending;
                }
        }

        unlock_timer(timr, flags);
        return ret;
}

static struct pid *good_sigevent(sigevent_t * event)
{
        struct task_struct *rtn = current->group_leader;

        if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
                (!(rtn = find_task_by_vpid(event->sigev_notify_thread_id)) ||
                 !same_thread_group(rtn, current) ||
                 (event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL))
                return NULL;

        if (((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) &&
            ((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))
                return NULL;

        return task_pid(rtn);
}

void posix_timers_register_clock(const clockid_t clock_id,
                                 struct k_clock *new_clock)
{
        if ((unsigned) clock_id >= MAX_CLOCKS) {
                printk(KERN_WARNING "POSIX clock register failed for clock_id %d\n",
                       clock_id);
                return;
        }

        if (!new_clock->clock_get) {
                printk(KERN_WARNING "POSIX clock id %d lacks clock_get()\n",
                       clock_id);
                return;
        }
        if (!new_clock->clock_getres) {
                printk(KERN_WARNING "POSIX clock id %d lacks clock_getres()\n",
                       clock_id);
                return;
        }

        posix_clocks[clock_id] = *new_clock;
}
EXPORT_SYMBOL_GPL(posix_timers_register_clock);

static struct k_itimer * alloc_posix_timer(void)
{
        struct k_itimer *tmr;
        tmr = kmem_cache_zalloc(posix_timers_cache, GFP_KERNEL);
        if (!tmr)
                return tmr;
        if (unlikely(!(tmr->sigq = sigqueue_alloc()))) {
                kmem_cache_free(posix_timers_cache, tmr);
                return NULL;
        }
        memset(&tmr->sigq->info, 0, sizeof(siginfo_t));
        return tmr;
}

static void k_itimer_rcu_free(struct rcu_head *head)
{
        struct k_itimer *tmr = container_of(head, struct k_itimer, it.rcu);

        kmem_cache_free(posix_timers_cache, tmr);
}

#define IT_ID_SET       1
#define IT_ID_NOT_SET   0
static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
{
        if (it_id_set) {
                unsigned long flags;
                spin_lock_irqsave(&hash_lock, flags);
                hlist_del_rcu(&tmr->t_hash);
                spin_unlock_irqrestore(&hash_lock, flags);
        }
        put_pid(tmr->it_pid);
        sigqueue_free(tmr->sigq);
        call_rcu(&tmr->it.rcu, k_itimer_rcu_free);
}

static struct k_clock *clockid_to_kclock(const clockid_t id)
{
        if (id < 0)
                return (id & CLOCKFD_MASK) == CLOCKFD ?
                        &clock_posix_dynamic : &clock_posix_cpu;

        if (id >= MAX_CLOCKS || !posix_clocks[id].clock_getres)
                return NULL;
        return &posix_clocks[id];
}

static int common_timer_create(struct k_itimer *new_timer)
{
        hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);
        return 0;
}

/* Create a POSIX.1b interval timer. */

SYSCALL_DEFINE3(timer_create, const clockid_t, which_clock,
                struct sigevent __user *, timer_event_spec,
                timer_t __user *, created_timer_id)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct k_itimer *new_timer;
        int error, new_timer_id;
        sigevent_t event;
        int it_id_set = IT_ID_NOT_SET;

        if (!kc)
                return -EINVAL;
        if (!kc->timer_create)
                return -EOPNOTSUPP;

        new_timer = alloc_posix_timer();
        if (unlikely(!new_timer))
                return -EAGAIN;

        spin_lock_init(&new_timer->it_lock);
        new_timer_id = posix_timer_add(new_timer);
        if (new_timer_id < 0) {
                error = new_timer_id;
                goto out;
        }

        it_id_set = IT_ID_SET;
        new_timer->it_id = (timer_t) new_timer_id;
        new_timer->it_clock = which_clock;
        new_timer->it_overrun = -1;

        if (timer_event_spec) {
                if (copy_from_user(&event, timer_event_spec, sizeof (event))) {
                        error = -EFAULT;
                        goto out;
                }
                rcu_read_lock();
                new_timer->it_pid = get_pid(good_sigevent(&event));
                rcu_read_unlock();
                if (!new_timer->it_pid) {
                        error = -EINVAL;
                        goto out;
                }
        } else {
                event.sigev_notify = SIGEV_SIGNAL;
                event.sigev_signo = SIGALRM;
                event.sigev_value.sival_int = new_timer->it_id;
                new_timer->it_pid = get_pid(task_tgid(current));
        }

        new_timer->it_sigev_notify     = event.sigev_notify;
        new_timer->sigq->info.si_signo = event.sigev_signo;
        new_timer->sigq->info.si_value = event.sigev_value;
        new_timer->sigq->info.si_tid   = new_timer->it_id;
        new_timer->sigq->info.si_code  = SI_TIMER;

        if (copy_to_user(created_timer_id,
                         &new_timer_id, sizeof (new_timer_id))) {
                error = -EFAULT;
                goto out;
        }

        error = kc->timer_create(new_timer);
        if (error)
                goto out;

        spin_lock_irq(&current->sighand->siglock);
        new_timer->it_signal = current->signal;
        list_add(&new_timer->list, &current->signal->posix_timers);
        spin_unlock_irq(&current->sighand->siglock);

        return 0;
        /*
         * In the case of the timer belonging to another task, after
         * the task is unlocked, the timer is owned by the other task
         * and may cease to exist at any time.  Don't use or modify
         * new_timer after the unlock call.
         */
out:
        release_posix_timer(new_timer, it_id_set);
        return error;
}

/*
 * Locking issues: We need to protect the result of the id look up until
 * we get the timer locked down so it is not deleted under us.  The
 * removal is done under the idr spinlock so we use that here to bridge
 * the find to the timer lock.  To avoid a dead lock, the timer id MUST
 * be release with out holding the timer lock.
 */
static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags)
{
        struct k_itimer *timr;

        /*
         * timer_t could be any type >= int and we want to make sure any
         * @timer_id outside positive int range fails lookup.
         */
        if ((unsigned long long)timer_id > INT_MAX)
                return NULL;

        rcu_read_lock();
        timr = posix_timer_by_id(timer_id);
        if (timr) {
                spin_lock_irqsave(&timr->it_lock, *flags);
                if (timr->it_signal == current->signal) {
                        rcu_read_unlock();
                        return timr;
                }
                spin_unlock_irqrestore(&timr->it_lock, *flags);
        }
        rcu_read_unlock();

        return NULL;
}

/*
 * Get the time remaining on a POSIX.1b interval timer.  This function
 * is ALWAYS called with spin_lock_irq on the timer, thus it must not
 * mess with irq.
 *
 * We have a couple of messes to clean up here.  First there is the case
 * of a timer that has a requeue pending.  These timers should appear to
 * be in the timer list with an expiry as if we were to requeue them
 * now.
 *
 * The second issue is the SIGEV_NONE timer which may be active but is
 * not really ever put in the timer list (to save system resources).
 * This timer may be expired, and if so, we will do it here.  Otherwise
 * it is the same as a requeue pending timer WRT to what we should
 * report.
 */
static void
common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting)
{
        ktime_t now, remaining, iv;
        struct hrtimer *timer = &timr->it.real.timer;

        memset(cur_setting, 0, sizeof(struct itimerspec));

        iv = timr->it.real.interval;

        /* interval timer ? */
        if (iv.tv64)
                cur_setting->it_interval = ktime_to_timespec(iv);
        else if (!hrtimer_active(timer) &&
                 (timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE)
                return;

        now = timer->base->get_time();

        /*
         * When a requeue is pending or this is a SIGEV_NONE
         * timer move the expiry time forward by intervals, so
         * expiry is > now.
         */
        if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING ||
            (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE))
                timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);

        remaining = ktime_sub(hrtimer_get_expires(timer), now);
        /* Return 0 only, when the timer is expired and not pending */
        if (remaining.tv64 <= 0) {
                /*
                 * A single shot SIGEV_NONE timer must return 0, when
                 * it is expired !
                 */
                if ((timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE)
                        cur_setting->it_value.tv_nsec = 1;
        } else
                cur_setting->it_value = ktime_to_timespec(remaining);
}

/* Get the time remaining on a POSIX.1b interval timer. */
SYSCALL_DEFINE2(timer_gettime, timer_t, timer_id,
                struct itimerspec __user *, setting)
{
        struct itimerspec cur_setting;
        struct k_itimer *timr;
        struct k_clock *kc;
        unsigned long flags;
        int ret = 0;

        timr = lock_timer(timer_id, &flags);
        if (!timr)
                return -EINVAL;

        kc = clockid_to_kclock(timr->it_clock);
        if (WARN_ON_ONCE(!kc || !kc->timer_get))
                ret = -EINVAL;
        else
                kc->timer_get(timr, &cur_setting);

        unlock_timer(timr, flags);

        if (!ret && copy_to_user(setting, &cur_setting, sizeof (cur_setting)))
                return -EFAULT;

        return ret;
}

/*
 * Get the number of overruns of a POSIX.1b interval timer.  This is to
 * be the overrun of the timer last delivered.  At the same time we are
 * accumulating overruns on the next timer.  The overrun is frozen when
 * the signal is delivered, either at the notify time (if the info block
 * is not queued) or at the actual delivery time (as we are informed by
 * the call back to do_schedule_next_timer().  So all we need to do is
 * to pick up the frozen overrun.
 */
SYSCALL_DEFINE1(timer_getoverrun, timer_t, timer_id)
{
        struct k_itimer *timr;
        int overrun;
        unsigned long flags;

        timr = lock_timer(timer_id, &flags);
        if (!timr)
                return -EINVAL;

        overrun = timr->it_overrun_last;
        unlock_timer(timr, flags);

        return overrun;
}

/* Set a POSIX.1b interval timer. */
/* timr->it_lock is taken. */
static int
common_timer_set(struct k_itimer *timr, int flags,
                 struct itimerspec *new_setting, struct itimerspec *old_setting)
{
        struct hrtimer *timer = &timr->it.real.timer;
        enum hrtimer_mode mode;

        if (old_setting)
                common_timer_get(timr, old_setting);

        /* disable the timer */
        timr->it.real.interval.tv64 = 0;
        /*
         * careful here.  If smp we could be in the "fire" routine which will
         * be spinning as we hold the lock.  But this is ONLY an SMP issue.
         */
        if (hrtimer_try_to_cancel(timer) < 0)
                return TIMER_RETRY;

        timr->it_requeue_pending = (timr->it_requeue_pending + 2) & 
                ~REQUEUE_PENDING;
        timr->it_overrun_last = 0;

        /* switch off the timer when it_value is zero */
        if (!new_setting->it_value.tv_sec && !new_setting->it_value.tv_nsec)
                return 0;

        mode = flags & TIMER_ABSTIME ? HRTIMER_MODE_ABS : HRTIMER_MODE_REL;
        hrtimer_init(&timr->it.real.timer, timr->it_clock, mode);
        timr->it.real.timer.function = posix_timer_fn;

        hrtimer_set_expires(timer, timespec_to_ktime(new_setting->it_value));

        /* Convert interval */
        timr->it.real.interval = timespec_to_ktime(new_setting->it_interval);

        /* SIGEV_NONE timers are not queued ! See common_timer_get */
        if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) {
                /* Setup correct expiry time for relative timers */
                if (mode == HRTIMER_MODE_REL) {
                        hrtimer_add_expires(timer, timer->base->get_time());
                }
                return 0;
        }

        hrtimer_start_expires(timer, mode);
        return 0;
}

/* Set a POSIX.1b interval timer */
SYSCALL_DEFINE4(timer_settime, timer_t, timer_id, int, flags,
                const struct itimerspec __user *, new_setting,
                struct itimerspec __user *, old_setting)
{
        struct k_itimer *timr;
        struct itimerspec new_spec, old_spec;
        int error = 0;
        unsigned long flag;
        struct itimerspec *rtn = old_setting ? &old_spec : NULL;
        struct k_clock *kc;

        if (!new_setting)
                return -EINVAL;

        if (copy_from_user(&new_spec, new_setting, sizeof (new_spec)))
                return -EFAULT;

        if (!timespec_valid(&new_spec.it_interval) ||
            !timespec_valid(&new_spec.it_value))
                return -EINVAL;
retry:
        timr = lock_timer(timer_id, &flag);
        if (!timr)
                return -EINVAL;

        kc = clockid_to_kclock(timr->it_clock);
        if (WARN_ON_ONCE(!kc || !kc->timer_set))
                error = -EINVAL;
        else
                error = kc->timer_set(timr, flags, &new_spec, rtn);

        unlock_timer(timr, flag);
        if (error == TIMER_RETRY) {
                rtn = NULL;     // We already got the old time...
                goto retry;
        }

        if (old_setting && !error &&
            copy_to_user(old_setting, &old_spec, sizeof (old_spec)))
                error = -EFAULT;

        return error;
}

static int common_timer_del(struct k_itimer *timer)
{
        timer->it.real.interval.tv64 = 0;

        if (hrtimer_try_to_cancel(&timer->it.real.timer) < 0)
                return TIMER_RETRY;
        return 0;
}

static inline int timer_delete_hook(struct k_itimer *timer)
{
        struct k_clock *kc = clockid_to_kclock(timer->it_clock);

        if (WARN_ON_ONCE(!kc || !kc->timer_del))
                return -EINVAL;
        return kc->timer_del(timer);
}

/* Delete a POSIX.1b interval timer. */
SYSCALL_DEFINE1(timer_delete, timer_t, timer_id)
{
        struct k_itimer *timer;
        unsigned long flags;

retry_delete:
        timer = lock_timer(timer_id, &flags);
        if (!timer)
                return -EINVAL;

        if (timer_delete_hook(timer) == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }

        spin_lock(&current->sighand->siglock);
        list_del(&timer->list);
        spin_unlock(&current->sighand->siglock);
        /*
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
        timer->it_signal = NULL;

        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);
        return 0;
}

/*
 * return timer owned by the process, used by exit_itimers
 */
static void itimer_delete(struct k_itimer *timer)
{
        unsigned long flags;

retry_delete:
        spin_lock_irqsave(&timer->it_lock, flags);

        if (timer_delete_hook(timer) == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }
        list_del(&timer->list);
        /*
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
        timer->it_signal = NULL;

        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);
}

/*
 * This is called by do_exit or de_thread, only when there are no more
 * references to the shared signal_struct.
 */
void exit_itimers(struct signal_struct *sig)
{
        struct k_itimer *tmr;

        while (!list_empty(&sig->posix_timers)) {
                tmr = list_entry(sig->posix_timers.next, struct k_itimer, list);
                itimer_delete(tmr);
        }
}

SYSCALL_DEFINE2(clock_settime, const clockid_t, which_clock,
                const struct timespec __user *, tp)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct timespec new_tp;

        if (!kc || !kc->clock_set)
                return -EINVAL;

        if (copy_from_user(&new_tp, tp, sizeof (*tp)))
                return -EFAULT;

        return kc->clock_set(which_clock, &new_tp);
}

SYSCALL_DEFINE2(clock_gettime, const clockid_t, which_clock,
                struct timespec __user *,tp)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct timespec kernel_tp;
        int error;

        if (!kc)
                return -EINVAL;

        error = kc->clock_get(which_clock, &kernel_tp);

        if (!error && copy_to_user(tp, &kernel_tp, sizeof (kernel_tp)))
                error = -EFAULT;

        return error;
}

SYSCALL_DEFINE2(clock_adjtime, const clockid_t, which_clock,
                struct timex __user *, utx)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct timex ktx;
        int err;

        if (!kc)
                return -EINVAL;
        if (!kc->clock_adj)
                return -EOPNOTSUPP;

        if (copy_from_user(&ktx, utx, sizeof(ktx)))
                return -EFAULT;

        err = kc->clock_adj(which_clock, &ktx);

        if (err >= 0 && copy_to_user(utx, &ktx, sizeof(ktx)))
                return -EFAULT;

        return err;
}

SYSCALL_DEFINE2(clock_getres, const clockid_t, which_clock,
                struct timespec __user *, tp)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct timespec rtn_tp;
        int error;

        if (!kc)
                return -EINVAL;

        error = kc->clock_getres(which_clock, &rtn_tp);

        if (!error && tp && copy_to_user(tp, &rtn_tp, sizeof (rtn_tp)))
                error = -EFAULT;

        return error;
}

/*
 * nanosleep for monotonic and realtime clocks
 */
static int common_nsleep(const clockid_t which_clock, int flags,
                         struct timespec *tsave, struct timespec __user *rmtp)
{
        return hrtimer_nanosleep(tsave, rmtp, flags & TIMER_ABSTIME ?
                                 HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
                                 which_clock);
}

SYSCALL_DEFINE4(clock_nanosleep, const clockid_t, which_clock, int, flags,
                const struct timespec __user *, rqtp,
                struct timespec __user *, rmtp)
{
        struct k_clock *kc = clockid_to_kclock(which_clock);
        struct timespec t;

        if (!kc)
                return -EINVAL;
        if (!kc->nsleep)
                return -ENANOSLEEP_NOTSUP;

        if (copy_from_user(&t, rqtp, sizeof (struct timespec)))
                return -EFAULT;

        if (!timespec_valid(&t))
                return -EINVAL;

        return kc->nsleep(which_clock, flags, &t, rmtp);
}

/*
 * This will restart clock_nanosleep. This is required only by
 * compat_clock_nanosleep_restart for now.
 */
long clock_nanosleep_restart(struct restart_block *restart_block)
{
        clockid_t which_clock = restart_block->nanosleep.clockid;
        struct k_clock *kc = clockid_to_kclock(which_clock);

        if (WARN_ON_ONCE(!kc || !kc->nsleep_restart))
                return -EINVAL;

        return kc->nsleep_restart(restart_block);
}