/*

   * 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/idr.h>
  #include <linux/posix-timers.h>
  #include <linux/syscalls.h>
  #include <linux/wait.h>
  #include <linux/workqueue.h>
  #include <linux/module.h>

  /*
   * 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 struct kmem_cache *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_pid

   *	    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];

  /*

   * These ones are defined below.

   */

  static int common_nsleep(const clockid_t, int flags, struct timespec *t,
  			 struct timespec __user *rmtp);
  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);
  
  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;
  }

  /*
   * Get real time for posix timers
   */
  static int common_clock_get(clockid_t which_clock, struct timespec *tp)

  {

  	ktime_get_real_ts(tp);

  	return 0;
  }

  static inline int common_clock_set(const clockid_t which_clock,
  				   struct timespec *tp)

  {
  	return do_sys_settimeofday(tp, NULL);
  }

  static int common_timer_create(struct k_itimer *new_timer)

  {

  	hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);

  	return 0;
  }

  static int no_timer_create(struct k_itimer *new_timer)
  {
  	return -EOPNOTSUPP;
  }

  /*

   * Return nonzero if 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;

  	if (posix_clocks[which_clock].res != 0)
  		return 0;

  	return 1;
  }

  /*
   * 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 time for posix timers
   */
  static int posix_get_monotonic_raw(clockid_t which_clock, struct timespec *tp)
  {
  	getrawmonotonic(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,

  	};

  	struct k_clock clock_monotonic = {
  		.clock_getres = hrtimer_get_res,
  		.clock_get = posix_ktime_get_ts,
  		.clock_set = do_posix_clock_nosettime,

  	};

  	struct k_clock clock_monotonic_raw = {
  		.clock_getres = hrtimer_get_res,
  		.clock_get = posix_get_monotonic_raw,
  		.clock_set = do_posix_clock_nosettime,

  		.timer_create = no_timer_create,

  	};

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

  	register_posix_clock(CLOCK_MONOTONIC_RAW, &clock_monotonic_raw);

  
  	posix_timers_cache = kmem_cache_create("posix_timers_cache",

  					sizeof (struct k_itimer), 0, SLAB_PANIC,
  					NULL);

  	idr_init(&posix_timers_id);
  	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 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) {
  		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 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
  ",
  		       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_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;
  }
  
  #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);
  	}

  	put_pid(tmr->it_pid);

  	sigqueue_free(tmr->sigq);

  	kmem_cache_free(posix_timers_cache, tmr);
  }
  
  /* 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_itimer *new_timer;

  	int error, new_timer_id;

  	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, new_timer, &new_timer_id);

  	spin_unlock_irq(&idr_lock);

  	if (error) {
  		if (error == -EAGAIN)
  			goto retry;

  		/*

  		 * Weird 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;
  		}

  		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;

  	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;
  	/*
  	 * 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 = idr_find(&posix_timers_id, (int)timer_id);

  	if (timr) {
  		spin_lock(&timr->it_lock);

  		if (timr->it_signal == current->signal) {

  			spin_unlock(&idr_lock);

  			return timr;
  		}
  		spin_unlock(&timr->it_lock);
  	}
  	spin_unlock_irqrestore(&idr_lock, *flags);

  	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 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.
   */

  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;
  
  	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;
  
  	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.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)
  {
  	return CLOCK_DISPATCH(timer->it_clock, 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);
  	}
  }

  /* Not available / possible... functions */

  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_nonanosleep(const clockid_t clock, int flags,

  			       struct timespec *t, struct timespec __user *r)

  {
  #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);

  SYSCALL_DEFINE2(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));
  }

  SYSCALL_DEFINE2(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;
  
  }

  SYSCALL_DEFINE2(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;
  }

  /*

   * 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 timespec t;

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

  	if (!timespec_valid(&t))

  		return -EINVAL;

  	return CLOCK_DISPATCH(which_clock, nsleep,
  			      (which_clock, flags, &t, rmtp));

  }

  
  /*
   * nanosleep_restart for monotonic and realtime clocks
   */
  static int common_nsleep_restart(struct restart_block *restart_block)
  {
  	return hrtimer_nanosleep_restart(restart_block);
  }
  
  /*
   * 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->arg0;
  
  	return CLOCK_DISPATCH(which_clock, nsleep_restart,
  			      (restart_block));
  }