[PATCH] hrtimer: create and use timespec_valid macro

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / posix-timers.c

/*
 * 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/smp_lock.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/calc64.h>

#include <asm/uaccess.h>
#include <asm/semaphore.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/idr.h>
#include <linux/posix-timers.h>
#include <linux/syscalls.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <linux/module.h>

#define CLOCK_REALTIME_RES TICK_NSEC  /* In nano seconds. */

static inline u64  mpy_l_X_l_ll(unsigned long mpy1,unsigned long mpy2)
{
        return (u64)mpy1 * mpy2;
}
/*
 * Management arrays for POSIX timers.   Timers are kept in slab memory
 * Timer ids are allocated by an external routine that keeps track of the
 * id and the timer.  The external interface is:
 *
 * void *idr_find(struct idr *idp, int id);           to find timer_id <id>
 * int idr_get_new(struct idr *idp, void *ptr);       to get a new id and
 *                                                    related it to <ptr>
 * void idr_remove(struct idr *idp, int id);          to release <id>
 * void idr_init(struct idr *idp);                    to initialize <idp>
 *                                                    which we supply.
 * The idr_get_new *may* call slab for more memory so it must not be
 * called under a spin lock.  Likewise idr_remore may release memory
 * (but it may be ok to do this under a lock...).
 * idr_find is just a memory look up and is quite fast.  A -1 return
 * indicates that the requested id does not exist.
 */

/*
 * Lets keep our timers in a slab cache :-)
 */
static kmem_cache_t *posix_timers_cache;
static struct idr posix_timers_id;
static DEFINE_SPINLOCK(idr_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


/*
 * 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 and allows the possibility of adding others.  We
 *          provide an interface to add clocks to the table and expect
 *          the "arch" code to add at least one clock that is high
 *          resolution.  Here we define the standard CLOCK_REALTIME as a
 *          1/HZ resolution clock.
 *
 * 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.  For clocks that use the standard
 *          system timer code these entries should be NULL.  This will
 *          allow dispatch without the overhead of indirect function
 *          calls.  CLOCKS that depend on other sources (e.g. WWV or GPS)
 *          must supply functions here, even if the function just returns
 *          ENOSYS.  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_process
 *          fields are not modified by timer code.
 *
 *          At this time all functions EXCEPT clock_nanosleep can be
 *          redirected by the CLOCKS structure.  Clock_nanosleep is in
 *          there, but the code ignores it.
 *
 * 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];
/*
 * We only have one real clock that can be set so we need only one abs list,
 * even if we should want to have several clocks with differing resolutions.
 */
static struct k_clock_abs abs_list = {.list = LIST_HEAD_INIT(abs_list.list),
                                      .lock = SPIN_LOCK_UNLOCKED};

static void posix_timer_fn(unsigned long);
static u64 do_posix_clock_monotonic_gettime_parts(
        struct timespec *tp, struct timespec *mo);
int do_posix_clock_monotonic_gettime(struct timespec *tp);
static int do_posix_clock_monotonic_get(const clockid_t, struct timespec *tp);

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

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

/*
 * Call the k_clock hook function if non-null, or the default function.
 */
#define CLOCK_DISPATCH(clock, call, arglist) \
        ((clock) < 0 ? posix_cpu_##call arglist : \
         (posix_clocks[clock].call != NULL \
          ? (*posix_clocks[clock].call) arglist : common_##call arglist))

/*
 * Default clock hook functions when the struct k_clock passed
 * to register_posix_clock leaves a function pointer null.
 *
 * The function common_CALL is the default implementation for
 * the function pointer CALL in struct k_clock.
 */

static inline int common_clock_getres(const clockid_t which_clock,
                                      struct timespec *tp)
{
        tp->tv_sec = 0;
        tp->tv_nsec = posix_clocks[which_clock].res;
        return 0;
}

static inline int common_clock_get(const clockid_t which_clock,
                                   struct timespec *tp)
{
        getnstimeofday(tp);
        return 0;
}

static inline int common_clock_set(const clockid_t which_clock,
                                   struct timespec *tp)
{
        return do_sys_settimeofday(tp, NULL);
}

static inline int common_timer_create(struct k_itimer *new_timer)
{
        INIT_LIST_HEAD(&new_timer->it.real.abs_timer_entry);
        init_timer(&new_timer->it.real.timer);
        new_timer->it.real.timer.data = (unsigned long) new_timer;
        new_timer->it.real.timer.function = posix_timer_fn;
        return 0;
}

/*
 * These ones are defined below.
 */
static int common_nsleep(const clockid_t, int flags, struct timespec *t);
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);

/*
 * Return nonzero iff we know a priori this clockid_t value is bogus.
 */
static inline int invalid_clockid(const clockid_t which_clock)
{
        if (which_clock < 0)    /* CPU clock, posix_cpu_* will check it */
                return 0;
        if ((unsigned) which_clock >= MAX_CLOCKS)
                return 1;
        if (posix_clocks[which_clock].clock_getres != NULL)
                return 0;
#ifndef CLOCK_DISPATCH_DIRECT
        if (posix_clocks[which_clock].res != 0)
                return 0;
#endif
        return 1;
}


/*
 * Initialize everything, well, just everything in Posix clocks/timers ;)
 */
static __init int init_posix_timers(void)
{
        struct k_clock clock_realtime = {.res = CLOCK_REALTIME_RES,
                                         .abs_struct = &abs_list
        };
        struct k_clock clock_monotonic = {.res = CLOCK_REALTIME_RES,
                .abs_struct = NULL,
                .clock_get = do_posix_clock_monotonic_get,
                .clock_set = do_posix_clock_nosettime
        };

        register_posix_clock(CLOCK_REALTIME, &clock_realtime);
        register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic);

        posix_timers_cache = kmem_cache_create("posix_timers_cache",
                                        sizeof (struct k_itimer), 0, 0, NULL, NULL);
        idr_init(&posix_timers_id);
        return 0;
}

__initcall(init_posix_timers);

static void tstojiffie(struct timespec *tp, int res, u64 *jiff)
{
        long sec = tp->tv_sec;
        long nsec = tp->tv_nsec + res - 1;

        if (nsec >= NSEC_PER_SEC) {
                sec++;
                nsec -= NSEC_PER_SEC;
        }

        /*
         * The scaling constants are defined in <linux/time.h>
         * The difference between there and here is that we do the
         * res rounding and compute a 64-bit result (well so does that
         * but it then throws away the high bits).
         */
        *jiff =  (mpy_l_X_l_ll(sec, SEC_CONVERSION) +
                  (mpy_l_X_l_ll(nsec, NSEC_CONVERSION) >> 
                   (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
}

/*
 * This function adjusts the timer as needed as a result of the clock
 * being set.  It should only be called for absolute timers, and then
 * under the abs_list lock.  It computes the time difference and sets
 * the new jiffies value in the timer.  It also updates the timers
 * reference wall_to_monotonic value.  It is complicated by the fact
 * that tstojiffies() only handles positive times and it needs to work
 * with both positive and negative times.  Also, for negative offsets,
 * we need to defeat the res round up.
 *
 * Return is true if there is a new time, else false.
 */
static long add_clockset_delta(struct k_itimer *timr,
                               struct timespec *new_wall_to)
{
        struct timespec delta;
        int sign = 0;
        u64 exp;

        set_normalized_timespec(&delta,
                                new_wall_to->tv_sec -
                                timr->it.real.wall_to_prev.tv_sec,
                                new_wall_to->tv_nsec -
                                timr->it.real.wall_to_prev.tv_nsec);
        if (likely(!(delta.tv_sec | delta.tv_nsec)))
                return 0;
        if (delta.tv_sec < 0) {
                set_normalized_timespec(&delta,
                                        -delta.tv_sec,
                                        1 - delta.tv_nsec -
                                        posix_clocks[timr->it_clock].res);
                sign++;
        }
        tstojiffie(&delta, posix_clocks[timr->it_clock].res, &exp);
        timr->it.real.wall_to_prev = *new_wall_to;
        timr->it.real.timer.expires += (sign ? -exp : exp);
        return 1;
}

static void remove_from_abslist(struct k_itimer *timr)
{
        if (!list_empty(&timr->it.real.abs_timer_entry)) {
                spin_lock(&abs_list.lock);
                list_del_init(&timr->it.real.abs_timer_entry);
                spin_unlock(&abs_list.lock);
        }
}

static void schedule_next_timer(struct k_itimer *timr)
{
        struct timespec new_wall_to;
        struct now_struct now;
        unsigned long seq;

        /*
         * Set up the timer for the next interval (if there is one).
         * Note: this code uses the abs_timer_lock to protect
         * it.real.wall_to_prev and must hold it until exp is set, not exactly
         * obvious...

         * This function is used for CLOCK_REALTIME* and
         * CLOCK_MONOTONIC* timers.  If we ever want to handle other
         * CLOCKs, the calling code (do_schedule_next_timer) would need
         * to pull the "clock" info from the timer and dispatch the
         * "other" CLOCKs "next timer" code (which, I suppose should
         * also be added to the k_clock structure).
         */
        if (!timr->it.real.incr)
                return;

        do {
                seq = read_seqbegin(&xtime_lock);
                new_wall_to =   wall_to_monotonic;
                posix_get_now(&now);
        } while (read_seqretry(&xtime_lock, seq));

        if (!list_empty(&timr->it.real.abs_timer_entry)) {
                spin_lock(&abs_list.lock);
                add_clockset_delta(timr, &new_wall_to);

                posix_bump_timer(timr, now);

                spin_unlock(&abs_list.lock);
        } else {
                posix_bump_timer(timr, now);
        }
        timr->it_overrun_last = timr->it_overrun;
        timr->it_overrun = -1;
        ++timr->it_requeue_pending;
        add_timer(&timr->it.real.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 aginst 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)
                goto exit;

        if (timr->it_clock < 0) /* CPU clock */
                posix_cpu_timer_schedule(timr);
        else
                schedule_next_timer(timr);
        info->si_overrun = timr->it_overrun_last;
exit:
        if (timr)
                unlock_timer(timr, flags);
}

int posix_timer_event(struct k_itimer *timr,int si_private)
{
        memset(&timr->sigq->info, 0, sizeof(siginfo_t));
        timr->sigq->info.si_sys_private = si_private;
        /*
         * Send signal to the process that owns this timer.

         * This code assumes that all the possible abs_lists share the
         * same lock (there is only one list at this time). If this is
         * not the case, the CLOCK info would need to be used to find
         * the proper abs list lock.
         */

        timr->sigq->info.si_signo = timr->it_sigev_signo;
        timr->sigq->info.si_errno = 0;
        timr->sigq->info.si_code = SI_TIMER;
        timr->sigq->info.si_tid = timr->it_id;
        timr->sigq->info.si_value = timr->it_sigev_value;

        if (timr->it_sigev_notify & SIGEV_THREAD_ID) {
                struct task_struct *leader;
                int ret = send_sigqueue(timr->it_sigev_signo, timr->sigq,
                                        timr->it_process);

                if (likely(ret >= 0))
                        return ret;

                timr->it_sigev_notify = SIGEV_SIGNAL;
                leader = timr->it_process->group_leader;
                put_task_struct(timr->it_process);
                timr->it_process = leader;
        }

        return send_group_sigqueue(timr->it_sigev_signo, timr->sigq,
                                   timr->it_process);
}
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 void posix_timer_fn(unsigned long __data)
{
        struct k_itimer *timr = (struct k_itimer *) __data;
        unsigned long flags;
        unsigned long seq;
        struct timespec delta, new_wall_to;
        u64 exp = 0;
        int do_notify = 1;

        spin_lock_irqsave(&timr->it_lock, flags);
        if (!list_empty(&timr->it.real.abs_timer_entry)) {
                spin_lock(&abs_list.lock);
                do {
                        seq = read_seqbegin(&xtime_lock);
                        new_wall_to =   wall_to_monotonic;
                } while (read_seqretry(&xtime_lock, seq));
                set_normalized_timespec(&delta,
                                        new_wall_to.tv_sec -
                                        timr->it.real.wall_to_prev.tv_sec,
                                        new_wall_to.tv_nsec -
                                        timr->it.real.wall_to_prev.tv_nsec);
                if (likely((delta.tv_sec | delta.tv_nsec ) == 0)) {
                        /* do nothing, timer is on time */
                } else if (delta.tv_sec < 0) {
                        /* do nothing, timer is already late */
                } else {
                        /* timer is early due to a clock set */
                        tstojiffie(&delta,
                                   posix_clocks[timr->it_clock].res,
                                   &exp);
                        timr->it.real.wall_to_prev = new_wall_to;
                        timr->it.real.timer.expires += exp;
                        add_timer(&timr->it.real.timer);
                        do_notify = 0;
                }
                spin_unlock(&abs_list.lock);

        }
        if (do_notify)  {
                int si_private=0;

                if (timr->it.real.incr)
                        si_private = ++timr->it_requeue_pending;
                else {
                        remove_from_abslist(timr);
                }

                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.
                         */
                        schedule_next_timer(timr);
        }
        unlock_timer(timr, flags); /* hold thru abs lock to keep irq off */
}


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

        if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
                (!(rtn = find_task_by_pid(event->sigev_notify_thread_id)) ||
                 rtn->tgid != current->tgid ||
                 (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 rtn;
}

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

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

static struct k_itimer * alloc_posix_timer(void)
{
        struct k_itimer *tmr;
        tmr = kmem_cache_alloc(posix_timers_cache, GFP_KERNEL);
        if (!tmr)
                return tmr;
        memset(tmr, 0, sizeof (struct k_itimer));
        if (unlikely(!(tmr->sigq = sigqueue_alloc()))) {
                kmem_cache_free(posix_timers_cache, tmr);
                tmr = NULL;
        }
        return 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(&idr_lock, flags);
                idr_remove(&posix_timers_id, tmr->it_id);
                spin_unlock_irqrestore(&idr_lock, flags);
        }
        sigqueue_free(tmr->sigq);
        if (unlikely(tmr->it_process) &&
            tmr->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
                put_task_struct(tmr->it_process);
        kmem_cache_free(posix_timers_cache, tmr);
}

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

asmlinkage long
sys_timer_create(const clockid_t which_clock,
                 struct sigevent __user *timer_event_spec,
                 timer_t __user * created_timer_id)
{
        int error = 0;
        struct k_itimer *new_timer = NULL;
        int new_timer_id;
        struct task_struct *process = NULL;
        unsigned long flags;
        sigevent_t event;
        int it_id_set = IT_ID_NOT_SET;

        if (invalid_clockid(which_clock))
                return -EINVAL;

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

        spin_lock_init(&new_timer->it_lock);
 retry:
        if (unlikely(!idr_pre_get(&posix_timers_id, GFP_KERNEL))) {
                error = -EAGAIN;
                goto out;
        }
        spin_lock_irq(&idr_lock);
        error = idr_get_new(&posix_timers_id,
                            (void *) new_timer,
                            &new_timer_id);
        spin_unlock_irq(&idr_lock);
        if (error == -EAGAIN)
                goto retry;
        else if (error) {
                /*
                 * Wierd looking, but we return EAGAIN if the IDR is
                 * full (proper POSIX return value for this)
                 */
                error = -EAGAIN;
                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;
        error = CLOCK_DISPATCH(which_clock, timer_create, (new_timer));
        if (error)
                goto out;

        /*
         * return the timer_id now.  The next step is hard to
         * back out if there is an error.
         */
        if (copy_to_user(created_timer_id,
                         &new_timer_id, sizeof (new_timer_id))) {
                error = -EFAULT;
                goto out;
        }
        if (timer_event_spec) {
                if (copy_from_user(&event, timer_event_spec, sizeof (event))) {
                        error = -EFAULT;
                        goto out;
                }
                new_timer->it_sigev_notify = event.sigev_notify;
                new_timer->it_sigev_signo = event.sigev_signo;
                new_timer->it_sigev_value = event.sigev_value;

                read_lock(&tasklist_lock);
                if ((process = good_sigevent(&event))) {
                        /*
                         * We may be setting up this process for another
                         * thread.  It may be exiting.  To catch this
                         * case the we check the PF_EXITING flag.  If
                         * the flag is not set, the siglock will catch
                         * him before it is too late (in exit_itimers).
                         *
                         * The exec case is a bit more invloved but easy
                         * to code.  If the process is in our thread
                         * group (and it must be or we would not allow
                         * it here) and is doing an exec, it will cause
                         * us to be killed.  In this case it will wait
                         * for us to die which means we can finish this
                         * linkage with our last gasp. I.e. no code :)
                         */
                        spin_lock_irqsave(&process->sighand->siglock, flags);
                        if (!(process->flags & PF_EXITING)) {
                                new_timer->it_process = process;
                                list_add(&new_timer->list,
                                         &process->signal->posix_timers);
                                spin_unlock_irqrestore(&process->sighand->siglock, flags);
                                if (new_timer->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
                                        get_task_struct(process);
                        } else {
                                spin_unlock_irqrestore(&process->sighand->siglock, flags);
                                process = NULL;
                        }
                }
                read_unlock(&tasklist_lock);
                if (!process) {
                        error = -EINVAL;
                        goto out;
                }
        } else {
                new_timer->it_sigev_notify = SIGEV_SIGNAL;
                new_timer->it_sigev_signo = SIGALRM;
                new_timer->it_sigev_value.sival_int = new_timer->it_id;
                process = current->group_leader;
                spin_lock_irqsave(&process->sighand->siglock, flags);
                new_timer->it_process = process;
                list_add(&new_timer->list, &process->signal->posix_timers);
                spin_unlock_irqrestore(&process->sighand->siglock, flags);
        }

        /*
         * 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:
        if (error)
                release_posix_timer(new_timer, it_id_set);

        return error;
}

/*
 * good_timespec
 *
 * This function checks the elements of a timespec structure.
 *
 * Arguments:
 * ts        : Pointer to the timespec structure to check
 *
 * Return value:
 * If a NULL pointer was passed in, or the tv_nsec field was less than 0
 * or greater than NSEC_PER_SEC, or the tv_sec field was less than 0,
 * this function returns 0. Otherwise it returns 1.
 */
static int good_timespec(const struct timespec *ts)
{
        if ((!ts) || !timespec_valid(ts))
                return 0;
        return 1;
}

/*
 * 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;
        /*
         * Watch out here.  We do a irqsave on the idr_lock and pass the
         * flags part over to the timer lock.  Must not let interrupts in
         * while we are moving the lock.
         */

        spin_lock_irqsave(&idr_lock, *flags);
        timr = (struct k_itimer *) idr_find(&posix_timers_id, (int) timer_id);
        if (timr) {
                spin_lock(&timr->it_lock);
                spin_unlock(&idr_lock);

                if ((timr->it_id != timer_id) || !(timr->it_process) ||
                                timr->it_process->tgid != current->tgid) {
                        unlock_timer(timr, *flags);
                        timr = NULL;
                }
        } else
                spin_unlock_irqrestore(&idr_lock, *flags);

        return timr;
}

/*
 * 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)
{
        unsigned long expires;
        struct now_struct now;

        do
                expires = timr->it.real.timer.expires;
        while ((volatile long) (timr->it.real.timer.expires) != expires);

        posix_get_now(&now);

        if (expires &&
            ((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) &&
            !timr->it.real.incr &&
            posix_time_before(&timr->it.real.timer, &now))
                timr->it.real.timer.expires = expires = 0;
        if (expires) {
                if (timr->it_requeue_pending & REQUEUE_PENDING ||
                    (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
                        posix_bump_timer(timr, now);
                        expires = timr->it.real.timer.expires;
                }
                else
                        if (!timer_pending(&timr->it.real.timer))
                                expires = 0;
                if (expires)
                        expires -= now.jiffies;
        }
        jiffies_to_timespec(expires, &cur_setting->it_value);
        jiffies_to_timespec(timr->it.real.incr, &cur_setting->it_interval);

        if (cur_setting->it_value.tv_sec < 0) {
                cur_setting->it_value.tv_nsec = 1;
                cur_setting->it_value.tv_sec = 0;
        }
}

/* Get the time remaining on a POSIX.1b interval timer. */
asmlinkage long
sys_timer_gettime(timer_t timer_id, struct itimerspec __user *setting)
{
        struct k_itimer *timr;
        struct itimerspec cur_setting;
        unsigned long flags;

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

        CLOCK_DISPATCH(timr->it_clock, timer_get, (timr, &cur_setting));

        unlock_timer(timr, flags);

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

        return 0;
}
/*
 * 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.
 */

asmlinkage long
sys_timer_getoverrun(timer_t timer_id)
{
        struct k_itimer *timr;
        int overrun;
        long flags;

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

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

        return overrun;
}
/*
 * Adjust for absolute time
 *
 * If absolute time is given and it is not CLOCK_MONOTONIC, we need to
 * adjust for the offset between the timer clock (CLOCK_MONOTONIC) and
 * what ever clock he is using.
 *
 * If it is relative time, we need to add the current (CLOCK_MONOTONIC)
 * time to it to get the proper time for the timer.
 */
static int adjust_abs_time(struct k_clock *clock, struct timespec *tp, 
                           int abs, u64 *exp, struct timespec *wall_to)
{
        struct timespec now;
        struct timespec oc = *tp;
        u64 jiffies_64_f;
        int rtn =0;

        if (abs) {
                /*
                 * The mask pick up the 4 basic clocks 
                 */
                if (!((clock - &posix_clocks[0]) & ~CLOCKS_MASK)) {
                        jiffies_64_f = do_posix_clock_monotonic_gettime_parts(
                                &now,  wall_to);
                        /*
                         * If we are doing a MONOTONIC clock
                         */
                        if((clock - &posix_clocks[0]) & CLOCKS_MONO){
                                now.tv_sec += wall_to->tv_sec;
                                now.tv_nsec += wall_to->tv_nsec;
                        }
                } else {
                        /*
                         * Not one of the basic clocks
                         */
                        clock->clock_get(clock - posix_clocks, &now);
                        jiffies_64_f = get_jiffies_64();
                }
                /*
                 * Take away now to get delta and normalize
                 */
                set_normalized_timespec(&oc, oc.tv_sec - now.tv_sec,
                                        oc.tv_nsec - now.tv_nsec);
        }else{
                jiffies_64_f = get_jiffies_64();
        }
        /*
         * Check if the requested time is prior to now (if so set now)
         */
        if (oc.tv_sec < 0)
                oc.tv_sec = oc.tv_nsec = 0;

        if (oc.tv_sec | oc.tv_nsec)
                set_normalized_timespec(&oc, oc.tv_sec,
                                        oc.tv_nsec + clock->res);
        tstojiffie(&oc, clock->res, exp);

        /*
         * Check if the requested time is more than the timer code
         * can handle (if so we error out but return the value too).
         */
        if (*exp > ((u64)MAX_JIFFY_OFFSET))
                        /*
                         * This is a considered response, not exactly in
                         * line with the standard (in fact it is silent on
                         * possible overflows).  We assume such a large 
                         * value is ALMOST always a programming error and
                         * try not to compound it by setting a really dumb
                         * value.
                         */
                        rtn = -EINVAL;
        /*
         * return the actual jiffies expire time, full 64 bits
         */
        *exp += jiffies_64_f;
        return rtn;
}

/* Set a POSIX.1b interval timer. */
/* timr->it_lock is taken. */
static inline int
common_timer_set(struct k_itimer *timr, int flags,
                 struct itimerspec *new_setting, struct itimerspec *old_setting)
{
        struct k_clock *clock = &posix_clocks[timr->it_clock];
        u64 expire_64;

        if (old_setting)
                common_timer_get(timr, old_setting);

        /* disable the timer */
        timr->it.real.incr = 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 (try_to_del_timer_sync(&timr->it.real.timer) < 0) {
#ifdef CONFIG_SMP
                /*
                 * It can only be active if on an other cpu.  Since
                 * we have cleared the interval stuff above, it should
                 * clear once we release the spin lock.  Of course once
                 * we do that anything could happen, including the
                 * complete melt down of the timer.  So return with
                 * a "retry" exit status.
                 */
                return TIMER_RETRY;
#endif
        }

        remove_from_abslist(timr);

        timr->it_requeue_pending = (timr->it_requeue_pending + 2) & 
                ~REQUEUE_PENDING;
        timr->it_overrun_last = 0;
        timr->it_overrun = -1;
        /*
         *switch off the timer when it_value is zero
         */
        if (!new_setting->it_value.tv_sec && !new_setting->it_value.tv_nsec) {
                timr->it.real.timer.expires = 0;
                return 0;
        }

        if (adjust_abs_time(clock,
                            &new_setting->it_value, flags & TIMER_ABSTIME, 
                            &expire_64, &(timr->it.real.wall_to_prev))) {
                return -EINVAL;
        }
        timr->it.real.timer.expires = (unsigned long)expire_64;
        tstojiffie(&new_setting->it_interval, clock->res, &expire_64);
        timr->it.real.incr = (unsigned long)expire_64;

        /*
         * We do not even queue SIGEV_NONE timers!  But we do put them
         * in the abs list so we can do that right.
         */
        if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE))
                add_timer(&timr->it.real.timer);

        if (flags & TIMER_ABSTIME && clock->abs_struct) {
                spin_lock(&clock->abs_struct->lock);
                list_add_tail(&(timr->it.real.abs_timer_entry),
                              &(clock->abs_struct->list));
                spin_unlock(&clock->abs_struct->lock);
        }
        return 0;
}

/* Set a POSIX.1b interval timer */
asmlinkage long
sys_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;
        long flag;
        struct itimerspec *rtn = old_setting ? &old_spec : NULL;

        if (!new_setting)
                return -EINVAL;

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

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

        error = CLOCK_DISPATCH(timr->it_clock, 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 inline int common_timer_del(struct k_itimer *timer)
{
        timer->it.real.incr = 0;

        if (try_to_del_timer_sync(&timer->it.real.timer) < 0) {
#ifdef CONFIG_SMP
                /*
                 * It can only be active if on an other cpu.  Since
                 * we have cleared the interval stuff above, it should
                 * clear once we release the spin lock.  Of course once
                 * we do that anything could happen, including the
                 * complete melt down of the timer.  So return with
                 * a "retry" exit status.
                 */
                return TIMER_RETRY;
#endif
        }

        remove_from_abslist(timer);

        return 0;
}

static inline int timer_delete_hook(struct k_itimer *timer)
{
        return CLOCK_DISPATCH(timer->it_clock, timer_del, (timer));
}

/* Delete a POSIX.1b interval timer. */
asmlinkage long
sys_timer_delete(timer_t timer_id)
{
        struct k_itimer *timer;
        long flags;

#ifdef CONFIG_SMP
        int error;
retry_delete:
#endif
        timer = lock_timer(timer_id, &flags);
        if (!timer)
                return -EINVAL;

#ifdef CONFIG_SMP
        error = timer_delete_hook(timer);

        if (error == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }
#else
        timer_delete_hook(timer);
#endif
        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).
         */
        if (timer->it_process) {
                if (timer->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
                        put_task_struct(timer->it_process);
                timer->it_process = 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 inline void itimer_delete(struct k_itimer *timer)
{
        unsigned long flags;

#ifdef CONFIG_SMP
        int error;
retry_delete:
#endif
        spin_lock_irqsave(&timer->it_lock, flags);

#ifdef CONFIG_SMP
        error = timer_delete_hook(timer);

        if (error == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }
#else
        timer_delete_hook(timer);
#endif
        list_del(&timer->list);
        /*
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
        if (timer->it_process) {
                if (timer->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
                        put_task_struct(timer->it_process);
                timer->it_process = 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);
        }
}

/*
 * And now for the "clock" calls
 *
 * These functions are called both from timer functions (with the timer
 * spin_lock_irq() held and from clock calls with no locking.   They must
 * use the save flags versions of locks.
 */

/*
 * We do ticks here to avoid the irq lock ( they take sooo long).
 * The seqlock is great here.  Since we a reader, we don't really care
 * if we are interrupted since we don't take lock that will stall us or
 * any other cpu. Voila, no irq lock is needed.
 *
 */

static u64 do_posix_clock_monotonic_gettime_parts(
        struct timespec *tp, struct timespec *mo)
{
        u64 jiff;
        unsigned int seq;

        do {
                seq = read_seqbegin(&xtime_lock);
                getnstimeofday(tp);
                *mo = wall_to_monotonic;
                jiff = jiffies_64;

        } while(read_seqretry(&xtime_lock, seq));

        return jiff;
}

static int do_posix_clock_monotonic_get(const clockid_t clock,
                                        struct timespec *tp)
{
        struct timespec wall_to_mono;

        do_posix_clock_monotonic_gettime_parts(tp, &wall_to_mono);

        set_normalized_timespec(tp, tp->tv_sec + wall_to_mono.tv_sec,
                                tp->tv_nsec + wall_to_mono.tv_nsec);

        return 0;
}

int do_posix_clock_monotonic_gettime(struct timespec *tp)
{
        return do_posix_clock_monotonic_get(CLOCK_MONOTONIC, tp);
}

int do_posix_clock_nosettime(const clockid_t clockid, struct timespec *tp)
{
        return -EINVAL;
}
EXPORT_SYMBOL_GPL(do_posix_clock_nosettime);

int do_posix_clock_notimer_create(struct k_itimer *timer)
{
        return -EINVAL;
}
EXPORT_SYMBOL_GPL(do_posix_clock_notimer_create);

int do_posix_clock_nonanosleep(const clockid_t clock, int flags,
                               struct timespec *t)
{
#ifndef ENOTSUP
        return -EOPNOTSUPP;     /* aka ENOTSUP in userland for POSIX */
#else  /*  parisc does define it separately.  */
        return -ENOTSUP;
#endif
}
EXPORT_SYMBOL_GPL(do_posix_clock_nonanosleep);

asmlinkage long sys_clock_settime(const clockid_t which_clock,
                                  const struct timespec __user *tp)
{
        struct timespec new_tp;

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

        return CLOCK_DISPATCH(which_clock, clock_set, (which_clock, &new_tp));
}

asmlinkage long
sys_clock_gettime(const clockid_t which_clock, struct timespec __user *tp)
{
        struct timespec kernel_tp;
        int error;

        if (invalid_clockid(which_clock))
                return -EINVAL;
        error = CLOCK_DISPATCH(which_clock, clock_get,
                               (which_clock, &kernel_tp));
        if (!error && copy_to_user(tp, &kernel_tp, sizeof (kernel_tp)))
                error = -EFAULT;

        return error;

}

asmlinkage long
sys_clock_getres(const clockid_t which_clock, struct timespec __user *tp)
{
        struct timespec rtn_tp;
        int error;

        if (invalid_clockid(which_clock))
                return -EINVAL;

        error = CLOCK_DISPATCH(which_clock, clock_getres,
                               (which_clock, &rtn_tp));

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

        return error;
}

/*
 * The standard says that an absolute nanosleep call MUST wake up at
 * the requested time in spite of clock settings.  Here is what we do:
 * For each nanosleep call that needs it (only absolute and not on
 * CLOCK_MONOTONIC* (as it can not be set)) we thread a little structure
 * into the "nanosleep_abs_list".  All we need is the task_struct pointer.
 * When ever the clock is set we just wake up all those tasks.   The rest
 * is done by the while loop in clock_nanosleep().
 *
 * On locking, clock_was_set() is called from update_wall_clock which
 * holds (or has held for it) a write_lock_irq( xtime_lock) and is
 * called from the timer bh code.  Thus we need the irq save locks.
 *
 * Also, on the call from update_wall_clock, that is done as part of a
 * softirq thing.  We don't want to delay the system that much (possibly
 * long list of timers to fix), so we defer that work to keventd.
 */

static DECLARE_WAIT_QUEUE_HEAD(nanosleep_abs_wqueue);
static DECLARE_WORK(clock_was_set_work, (void(*)(void*))clock_was_set, NULL);

static DECLARE_MUTEX(clock_was_set_lock);

void clock_was_set(void)
{
        struct k_itimer *timr;
        struct timespec new_wall_to;
        LIST_HEAD(cws_list);
        unsigned long seq;


        if (unlikely(in_interrupt())) {
                schedule_work(&clock_was_set_work);
                return;
        }
        wake_up_all(&nanosleep_abs_wqueue);

        /*
         * Check if there exist TIMER_ABSTIME timers to correct.
         *
         * Notes on locking: This code is run in task context with irq
         * on.  We CAN be interrupted!  All other usage of the abs list
         * lock is under the timer lock which holds the irq lock as
         * well.  We REALLY don't want to scan the whole list with the
         * interrupt system off, AND we would like a sequence lock on
         * this code as well.  Since we assume that the clock will not
         * be set often, it seems ok to take and release the irq lock
         * for each timer.  In fact add_timer will do this, so this is
         * not an issue.  So we know when we are done, we will move the
         * whole list to a new location.  Then as we process each entry,
         * we will move it to the actual list again.  This way, when our
         * copy is empty, we are done.  We are not all that concerned
         * about preemption so we will use a semaphore lock to protect
         * aginst reentry.  This way we will not stall another
         * processor.  It is possible that this may delay some timers
         * that should have expired, given the new clock, but even this
         * will be minimal as we will always update to the current time,
         * even if it was set by a task that is waiting for entry to
         * this code.  Timers that expire too early will be caught by
         * the expire code and restarted.

         * Absolute timers that repeat are left in the abs list while
         * waiting for the task to pick up the signal.  This means we
         * may find timers that are not in the "add_timer" list, but are
         * in the abs list.  We do the same thing for these, save
         * putting them back in the "add_timer" list.  (Note, these are
         * left in the abs list mainly to indicate that they are
         * ABSOLUTE timers, a fact that is used by the re-arm code, and
         * for which we have no other flag.)

         */

        down(&clock_was_set_lock);
        spin_lock_irq(&abs_list.lock);
        list_splice_init(&abs_list.list, &cws_list);
        spin_unlock_irq(&abs_list.lock);
        do {
                do {
                        seq = read_seqbegin(&xtime_lock);
                        new_wall_to =   wall_to_monotonic;
                } while (read_seqretry(&xtime_lock, seq));

                spin_lock_irq(&abs_list.lock);
                if (list_empty(&cws_list)) {
                        spin_unlock_irq(&abs_list.lock);
                        break;
                }
                timr = list_entry(cws_list.next, struct k_itimer,
                                  it.real.abs_timer_entry);

                list_del_init(&timr->it.real.abs_timer_entry);
                if (add_clockset_delta(timr, &new_wall_to) &&
                    del_timer(&timr->it.real.timer))  /* timer run yet? */
                        add_timer(&timr->it.real.timer);
                list_add(&timr->it.real.abs_timer_entry, &abs_list.list);
                spin_unlock_irq(&abs_list.lock);
        } while (1);

        up(&clock_was_set_lock);
}

long clock_nanosleep_restart(struct restart_block *restart_block);

asmlinkage long
sys_clock_nanosleep(const clockid_t which_clock, int flags,
                    const struct timespec __user *rqtp,
                    struct timespec __user *rmtp)
{
        struct timespec t;
        struct restart_block *restart_block =
            &(current_thread_info()->restart_block);
        int ret;

        if (invalid_clockid(which_clock))
                return -EINVAL;

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

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

        /*
         * Do this here as nsleep function does not have the real address.
         */
        restart_block->arg1 = (unsigned long)rmtp;

        ret = CLOCK_DISPATCH(which_clock, nsleep, (which_clock, flags, &t));

        if ((ret == -ERESTART_RESTARTBLOCK) && rmtp &&
                                        copy_to_user(rmtp, &t, sizeof (t)))
                return -EFAULT;
        return ret;
}


static int common_nsleep(const clockid_t which_clock,
                         int flags, struct timespec *tsave)
{
        struct timespec t, dum;
        DECLARE_WAITQUEUE(abs_wqueue, current);
        u64 rq_time = (u64)0;
        s64 left;
        int abs;
        struct restart_block *restart_block =
            &current_thread_info()->restart_block;

        abs_wqueue.flags = 0;
        abs = flags & TIMER_ABSTIME;

        if (restart_block->fn == clock_nanosleep_restart) {
                /*
                 * Interrupted by a non-delivered signal, pick up remaining
                 * time and continue.  Remaining time is in arg2 & 3.
                 */
                restart_block->fn = do_no_restart_syscall;

                rq_time = restart_block->arg3;
                rq_time = (rq_time << 32) + restart_block->arg2;
                if (!rq_time)
                        return -EINTR;
                left = rq_time - get_jiffies_64();
                if (left <= (s64)0)
                        return 0;       /* Already passed */
        }

        if (abs && (posix_clocks[which_clock].clock_get !=
                            posix_clocks[CLOCK_MONOTONIC].clock_get))
                add_wait_queue(&nanosleep_abs_wqueue, &abs_wqueue);

        do {
                t = *tsave;
                if (abs || !rq_time) {
                        adjust_abs_time(&posix_clocks[which_clock], &t, abs,
                                        &rq_time, &dum);
                }

                left = rq_time - get_jiffies_64();
                if (left >= (s64)MAX_JIFFY_OFFSET)
                        left = (s64)MAX_JIFFY_OFFSET;
                if (left < (s64)0)
                        break;

                schedule_timeout_interruptible(left);

                left = rq_time - get_jiffies_64();
        } while (left > (s64)0 && !test_thread_flag(TIF_SIGPENDING));

        if (abs_wqueue.task_list.next)
                finish_wait(&nanosleep_abs_wqueue, &abs_wqueue);

        if (left > (s64)0) {

                /*
                 * Always restart abs calls from scratch to pick up any
                 * clock shifting that happened while we are away.
                 */
                if (abs)
                        return -ERESTARTNOHAND;

                left *= TICK_NSEC;
                tsave->tv_sec = div_long_long_rem(left, 
                                                  NSEC_PER_SEC, 
                                                  &tsave->tv_nsec);
                /*
                 * Restart works by saving the time remaing in 
                 * arg2 & 3 (it is 64-bits of jiffies).  The other
                 * info we need is the clock_id (saved in arg0). 
                 * The sys_call interface needs the users 
                 * timespec return address which _it_ saves in arg1.
                 * Since we have cast the nanosleep call to a clock_nanosleep
                 * both can be restarted with the same code.
                 */
                restart_block->fn = clock_nanosleep_restart;
                restart_block->arg0 = which_clock;
                /*
                 * Caller sets arg1
                 */
                restart_block->arg2 = rq_time & 0xffffffffLL;
                restart_block->arg3 = rq_time >> 32;

                return -ERESTART_RESTARTBLOCK;
        }

        return 0;
}
/*
 * This will restart clock_nanosleep.
 */
long
clock_nanosleep_restart(struct restart_block *restart_block)
{
        struct timespec t;
        int ret = common_nsleep(restart_block->arg0, 0, &t);

        if ((ret == -ERESTART_RESTARTBLOCK) && restart_block->arg1 &&
            copy_to_user((struct timespec __user *)(restart_block->arg1), &t,
                         sizeof (t)))
                return -EFAULT;
        return ret;
}