/*
   * linux/kernel/itimer.c
   *
   * Copyright (C) 1992 Darren Senn
   */
  
  /* These are all the functions necessary to implement itimers */
  
  #include <linux/mm.h>

  #include <linux/interrupt.h>
  #include <linux/syscalls.h>
  #include <linux/time.h>
  #include <linux/posix-timers.h>

  #include <linux/hrtimer.h>

  #include <trace/events/timer.h>

  
  #include <asm/uaccess.h>

  /**
   * itimer_get_remtime - get remaining time for the timer
   *
   * @timer: the timer to read
   *
   * Returns the delta between the expiry time and now, which can be
   * less than zero or 1usec for an pending expired timer
   */
  static struct timeval itimer_get_remtime(struct hrtimer *timer)

  {

  	ktime_t rem = hrtimer_get_remaining(timer);

  	/*
  	 * Racy but safe: if the itimer expires after the above
  	 * hrtimer_get_remtime() call but before this condition
  	 * then we return 0 - which is correct.
  	 */
  	if (hrtimer_active(timer)) {
  		if (rem.tv64 <= 0)
  			rem.tv64 = NSEC_PER_USEC;
  	} else
  		rem.tv64 = 0;
  
  	return ktime_to_timeval(rem);

  }

  static void get_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,

  			   struct itimerval *const value)

  {
  	cputime_t cval, cinterval;
  	struct cpu_itimer *it = &tsk->signal->it[clock_id];
  
  	spin_lock_irq(&tsk->sighand->siglock);
  
  	cval = it->expires;
  	cinterval = it->incr;

  	if (cval) {

  		struct task_cputime cputime;
  		cputime_t t;
  
  		thread_group_cputimer(tsk, &cputime);
  		if (clock_id == CPUCLOCK_PROF)

  			t = cputime.utime + cputime.stime;

  		else
  			/* CPUCLOCK_VIRT */
  			t = cputime.utime;

  		if (cval < t)

  			/* about to fire */

  			cval = cputime_one_jiffy;

  		else

  			cval = cval - t;

  	}
  
  	spin_unlock_irq(&tsk->sighand->siglock);
  
  	cputime_to_timeval(cval, &value->it_value);
  	cputime_to_timeval(cinterval, &value->it_interval);
  }

  int do_getitimer(int which, struct itimerval *value)
  {
  	struct task_struct *tsk = current;

  
  	switch (which) {
  	case ITIMER_REAL:

  		spin_lock_irq(&tsk->sighand->siglock);

  		value->it_value = itimer_get_remtime(&tsk->signal->real_timer);
  		value->it_interval =
  			ktime_to_timeval(tsk->signal->it_real_incr);

  		spin_unlock_irq(&tsk->sighand->siglock);

  		break;
  	case ITIMER_VIRTUAL:

  		get_cpu_itimer(tsk, CPUCLOCK_VIRT, value);

  		break;
  	case ITIMER_PROF:

  		get_cpu_itimer(tsk, CPUCLOCK_PROF, value);

  		break;
  	default:
  		return(-EINVAL);
  	}
  	return 0;
  }

  SYSCALL_DEFINE2(getitimer, int, which, struct itimerval __user *, value)

  {
  	int error = -EFAULT;
  	struct itimerval get_buffer;
  
  	if (value) {
  		error = do_getitimer(which, &get_buffer);
  		if (!error &&
  		    copy_to_user(value, &get_buffer, sizeof(get_buffer)))
  			error = -EFAULT;
  	}
  	return error;
  }

  /*
   * The timer is automagically restarted, when interval != 0
   */

  enum hrtimer_restart it_real_fn(struct hrtimer *timer)

  {

  	struct signal_struct *sig =

  		container_of(timer, struct signal_struct, real_timer);

  	trace_itimer_expire(ITIMER_REAL, sig->leader_pid, 0);

  	kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);

  	return HRTIMER_NORESTART;

  }

  static inline u32 cputime_sub_ns(cputime_t ct, s64 real_ns)
  {
  	struct timespec ts;
  	s64 cpu_ns;
  
  	cputime_to_timespec(ct, &ts);
  	cpu_ns = timespec_to_ns(&ts);
  
  	return (cpu_ns <= real_ns) ? 0 : cpu_ns - real_ns;
  }

  static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,

  			   const struct itimerval *const value,
  			   struct itimerval *const ovalue)

  {

  	cputime_t cval, nval, cinterval, ninterval;
  	s64 ns_ninterval, ns_nval;

  	u32 error, incr_error;

  	struct cpu_itimer *it = &tsk->signal->it[clock_id];
  
  	nval = timeval_to_cputime(&value->it_value);

  	ns_nval = timeval_to_ns(&value->it_value);

  	ninterval = timeval_to_cputime(&value->it_interval);

  	ns_ninterval = timeval_to_ns(&value->it_interval);

  	error = cputime_sub_ns(nval, ns_nval);
  	incr_error = cputime_sub_ns(ninterval, ns_ninterval);

  
  	spin_lock_irq(&tsk->sighand->siglock);
  
  	cval = it->expires;
  	cinterval = it->incr;

  	if (cval || nval) {
  		if (nval > 0)
  			nval += cputime_one_jiffy;

  		set_process_cpu_timer(tsk, clock_id, &nval, &cval);
  	}
  	it->expires = nval;
  	it->incr = ninterval;

  	it->error = error;
  	it->incr_error = incr_error;

  	trace_itimer_state(clock_id == CPUCLOCK_VIRT ?
  			   ITIMER_VIRTUAL : ITIMER_PROF, value, nval);

  
  	spin_unlock_irq(&tsk->sighand->siglock);
  
  	if (ovalue) {
  		cputime_to_timeval(cval, &ovalue->it_value);
  		cputime_to_timeval(cinterval, &ovalue->it_interval);
  	}
  }

  /*

   * Returns true if the timeval is in canonical form
   */
  #define timeval_valid(t) \
  	(((t)->tv_sec >= 0) && (((unsigned long) (t)->tv_usec) < USEC_PER_SEC))

  int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
  {
  	struct task_struct *tsk = current;

  	struct hrtimer *timer;
  	ktime_t expires;

  	/*
  	 * Validate the timevals in value.

  	 */

  	if (!timeval_valid(&value->it_value) ||
  	    !timeval_valid(&value->it_interval))
  		return -EINVAL;

  	switch (which) {
  	case ITIMER_REAL:

  again:
  		spin_lock_irq(&tsk->sighand->siglock);

  		timer = &tsk->signal->real_timer;

  		if (ovalue) {

  			ovalue->it_value = itimer_get_remtime(timer);
  			ovalue->it_interval
  				= ktime_to_timeval(tsk->signal->it_real_incr);

  		}

  		/* We are sharing ->siglock with it_real_fn() */
  		if (hrtimer_try_to_cancel(timer) < 0) {
  			spin_unlock_irq(&tsk->sighand->siglock);
  			goto again;
  		}

  		expires = timeval_to_ktime(value->it_value);

  		if (expires.tv64 != 0) {
  			tsk->signal->it_real_incr =
  				timeval_to_ktime(value->it_interval);

  			hrtimer_start(timer, expires, HRTIMER_MODE_REL);

  		} else
  			tsk->signal->it_real_incr.tv64 = 0;

  		trace_itimer_state(ITIMER_REAL, value, 0);

  		spin_unlock_irq(&tsk->sighand->siglock);

  		break;
  	case ITIMER_VIRTUAL:

  		set_cpu_itimer(tsk, CPUCLOCK_VIRT, value, ovalue);

  		break;
  	case ITIMER_PROF:

  		set_cpu_itimer(tsk, CPUCLOCK_PROF, value, ovalue);

  		break;
  	default:
  		return -EINVAL;
  	}
  	return 0;
  }

  /**
   * alarm_setitimer - set alarm in seconds
   *
   * @seconds:	number of seconds until alarm
   *		0 disables the alarm
   *
   * Returns the remaining time in seconds of a pending timer or 0 when
   * the timer is not active.
   *
   * On 32 bit machines the seconds value is limited to (INT_MAX/2) to avoid
   * negative timeval settings which would cause immediate expiry.
   */
  unsigned int alarm_setitimer(unsigned int seconds)
  {
  	struct itimerval it_new, it_old;
  
  #if BITS_PER_LONG < 64
  	if (seconds > INT_MAX)
  		seconds = INT_MAX;
  #endif
  	it_new.it_value.tv_sec = seconds;
  	it_new.it_value.tv_usec = 0;
  	it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
  
  	do_setitimer(ITIMER_REAL, &it_new, &it_old);
  
  	/*
  	 * We can't return 0 if we have an alarm pending ...  And we'd
  	 * better return too much than too little anyway
  	 */
  	if ((!it_old.it_value.tv_sec && it_old.it_value.tv_usec) ||
  	      it_old.it_value.tv_usec >= 500000)
  		it_old.it_value.tv_sec++;
  
  	return it_old.it_value.tv_sec;
  }

  SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
  		struct itimerval __user *, ovalue)

  {
  	struct itimerval set_buffer, get_buffer;
  	int error;
  
  	if (value) {
  		if(copy_from_user(&set_buffer, value, sizeof(set_buffer)))
  			return -EFAULT;
  	} else
  		memset((char *) &set_buffer, 0, sizeof(set_buffer));
  
  	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
  	if (error || !ovalue)
  		return error;
  
  	if (copy_to_user(ovalue, &get_buffer, sizeof(get_buffer)))

  		return -EFAULT;

  	return 0;
  }