/*
   *  linux/kernel/time.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *
   *  This file contains the interface functions for the various
   *  time related system calls: time, stime, gettimeofday, settimeofday,
   *			       adjtime
   */
  /*
   * Modification history kernel/time.c

   *

   * 1993-09-02    Philip Gladstone

   *      Created file with time related functions from sched.c and adjtimex()

   * 1993-10-08    Torsten Duwe
   *      adjtime interface update and CMOS clock write code
   * 1995-08-13    Torsten Duwe
   *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
   * 1999-01-16    Ulrich Windl
   *	Introduced error checking for many cases in adjtimex().
   *	Updated NTP code according to technical memorandum Jan '96
   *	"A Kernel Model for Precision Timekeeping" by Dave Mills
   *	Allow time_constant larger than MAXTC(6) for NTP v4 (MAXTC == 10)
   *	(Even though the technical memorandum forbids it)
   * 2004-07-14	 Christoph Lameter
   *	Added getnstimeofday to allow the posix timer functions to return
   *	with nanosecond accuracy
   */

  #include <linux/export.h>

  #include <linux/timex.h>

  #include <linux/capability.h>

  #include <linux/clocksource.h>

  #include <linux/errno.h>

  #include <linux/syscalls.h>
  #include <linux/security.h>
  #include <linux/fs.h>

  #include <linux/math64.h>

  #include <linux/ptrace.h>

  
  #include <asm/uaccess.h>
  #include <asm/unistd.h>

  #include "timeconst.h"

  /*

   * The timezone where the local system is located.  Used as a default by some
   * programs who obtain this value by using gettimeofday.
   */
  struct timezone sys_tz;
  
  EXPORT_SYMBOL(sys_tz);
  
  #ifdef __ARCH_WANT_SYS_TIME
  
  /*
   * sys_time() can be implemented in user-level using
   * sys_gettimeofday().  Is this for backwards compatibility?  If so,
   * why not move it into the appropriate arch directory (for those
   * architectures that need it).
   */

  SYSCALL_DEFINE1(time, time_t __user *, tloc)

  {

  	time_t i = get_seconds();

  
  	if (tloc) {

  		if (put_user(i,tloc))

  			return -EFAULT;

  	}

  	force_successful_syscall_return();

  	return i;
  }
  
  /*
   * sys_stime() can be implemented in user-level using
   * sys_settimeofday().  Is this for backwards compatibility?  If so,
   * why not move it into the appropriate arch directory (for those
   * architectures that need it).
   */

  SYSCALL_DEFINE1(stime, time_t __user *, tptr)

  {
  	struct timespec tv;
  	int err;
  
  	if (get_user(tv.tv_sec, tptr))
  		return -EFAULT;
  
  	tv.tv_nsec = 0;
  
  	err = security_settime(&tv, NULL);
  	if (err)
  		return err;
  
  	do_settimeofday(&tv);
  	return 0;
  }
  
  #endif /* __ARCH_WANT_SYS_TIME */

  SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
  		struct timezone __user *, tz)

  {
  	if (likely(tv != NULL)) {
  		struct timeval ktv;
  		do_gettimeofday(&ktv);
  		if (copy_to_user(tv, &ktv, sizeof(ktv)))
  			return -EFAULT;
  	}
  	if (unlikely(tz != NULL)) {
  		if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
  			return -EFAULT;
  	}
  	return 0;
  }
  
  /*
   * Adjust the time obtained from the CMOS to be UTC time instead of
   * local time.

   *

   * This is ugly, but preferable to the alternatives.  Otherwise we
   * would either need to write a program to do it in /etc/rc (and risk

   * confusion if the program gets run more than once; it would also be

   * hard to make the program warp the clock precisely n hours)  or
   * compile in the timezone information into the kernel.  Bad, bad....
   *

   *						- TYT, 1992-01-01

   *
   * The best thing to do is to keep the CMOS clock in universal time (UTC)
   * as real UNIX machines always do it. This avoids all headaches about
   * daylight saving times and warping kernel clocks.
   */

  static inline void warp_clock(void)

  {

  	struct timespec adjust;
  
  	adjust = current_kernel_time();
  	adjust.tv_sec += sys_tz.tz_minuteswest * 60;

  	do_settimeofday(&adjust);

  }
  
  /*
   * In case for some reason the CMOS clock has not already been running
   * in UTC, but in some local time: The first time we set the timezone,
   * we will warp the clock so that it is ticking UTC time instead of
   * local time. Presumably, if someone is setting the timezone then we
   * are running in an environment where the programs understand about
   * timezones. This should be done at boot time in the /etc/rc script,
   * as soon as possible, so that the clock can be set right. Otherwise,
   * various programs will get confused when the clock gets warped.
   */

  int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)

  {
  	static int firsttime = 1;
  	int error = 0;

  	if (tv && !timespec_valid(tv))

  		return -EINVAL;

  	error = security_settime(tv, tz);
  	if (error)
  		return error;
  
  	if (tz) {

  		sys_tz = *tz;

  		update_vsyscall_tz();

  		if (firsttime) {
  			firsttime = 0;
  			if (!tv)
  				warp_clock();
  		}
  	}
  	if (tv)

  		return do_settimeofday(tv);

  	return 0;
  }

  SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
  		struct timezone __user *, tz)

  {
  	struct timeval user_tv;
  	struct timespec	new_ts;
  	struct timezone new_tz;
  
  	if (tv) {
  		if (copy_from_user(&user_tv, tv, sizeof(*tv)))
  			return -EFAULT;
  		new_ts.tv_sec = user_tv.tv_sec;
  		new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
  	}
  	if (tz) {
  		if (copy_from_user(&new_tz, tz, sizeof(*tz)))
  			return -EFAULT;
  	}
  
  	return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
  }

  SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)

  {
  	struct timex txc;		/* Local copy of parameter */
  	int ret;
  
  	/* Copy the user data space into the kernel copy
  	 * structure. But bear in mind that the structures
  	 * may change
  	 */
  	if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
  		return -EFAULT;
  	ret = do_adjtimex(&txc);
  	return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
  }

  /**
   * current_fs_time - Return FS time
   * @sb: Superblock.
   *

   * Return the current time truncated to the time granularity supported by

   * the fs.
   */
  struct timespec current_fs_time(struct super_block *sb)
  {
  	struct timespec now = current_kernel_time();
  	return timespec_trunc(now, sb->s_time_gran);
  }
  EXPORT_SYMBOL(current_fs_time);

  /*
   * Convert jiffies to milliseconds and back.
   *
   * Avoid unnecessary multiplications/divisions in the
   * two most common HZ cases:
   */

  inline unsigned int jiffies_to_msecs(const unsigned long j)

  {
  #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
  	return (MSEC_PER_SEC / HZ) * j;
  #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
  	return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
  #else

  # if BITS_PER_LONG == 32

  	return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;

  # else
  	return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
  # endif

  #endif
  }
  EXPORT_SYMBOL(jiffies_to_msecs);

  inline unsigned int jiffies_to_usecs(const unsigned long j)

  {
  #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
  	return (USEC_PER_SEC / HZ) * j;
  #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
  	return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
  #else

  # if BITS_PER_LONG == 32

  	return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;

  # else
  	return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
  # endif

  #endif
  }
  EXPORT_SYMBOL(jiffies_to_usecs);

  /**

   * timespec_trunc - Truncate timespec to a granularity

   * @t: Timespec

   * @gran: Granularity in ns.

   *

   * Truncate a timespec to a granularity. gran must be smaller than a second.

   * Always rounds down.
   *
   * This function should be only used for timestamps returned by
   * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because

   * it doesn't handle the better resolution of the latter.

   */
  struct timespec timespec_trunc(struct timespec t, unsigned gran)
  {
  	/*
  	 * Division is pretty slow so avoid it for common cases.
  	 * Currently current_kernel_time() never returns better than
  	 * jiffies resolution. Exploit that.
  	 */
  	if (gran <= jiffies_to_usecs(1) * 1000) {
  		/* nothing */
  	} else if (gran == 1000000000) {
  		t.tv_nsec = 0;
  	} else {
  		t.tv_nsec -= t.tv_nsec % gran;
  	}
  	return t;
  }
  EXPORT_SYMBOL(timespec_trunc);

  /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
   * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
   * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
   *
   * [For the Julian calendar (which was used in Russia before 1917,
   * Britain & colonies before 1752, anywhere else before 1582,
   * and is still in use by some communities) leave out the
   * -year/100+year/400 terms, and add 10.]
   *
   * This algorithm was first published by Gauss (I think).
   *
   * WARNING: this function will overflow on 2106-02-07 06:28:16 on

   * machines where long is 32-bit! (However, as time_t is signed, we

   * will already get problems at other places on 2038-01-19 03:14:08)
   */
  unsigned long

  mktime(const unsigned int year0, const unsigned int mon0,
         const unsigned int day, const unsigned int hour,
         const unsigned int min, const unsigned int sec)

  {

  	unsigned int mon = mon0, year = year0;
  
  	/* 1..12 -> 11,12,1..10 */
  	if (0 >= (int) (mon -= 2)) {
  		mon += 12;	/* Puts Feb last since it has leap day */

  		year -= 1;
  	}
  
  	return ((((unsigned long)
  		  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
  		  year*365 - 719499
  	    )*24 + hour /* now have hours */
  	  )*60 + min /* now have minutes */
  	)*60 + sec; /* finally seconds */
  }

  EXPORT_SYMBOL(mktime);

  /**
   * set_normalized_timespec - set timespec sec and nsec parts and normalize
   *
   * @ts:		pointer to timespec variable to be set
   * @sec:	seconds to set
   * @nsec:	nanoseconds to set
   *
   * Set seconds and nanoseconds field of a timespec variable and
   * normalize to the timespec storage format
   *
   * Note: The tv_nsec part is always in the range of

   *	0 <= tv_nsec < NSEC_PER_SEC

   * For negative values only the tv_sec field is negative !
   */

  void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)

  {
  	while (nsec >= NSEC_PER_SEC) {

  		/*
  		 * The following asm() prevents the compiler from
  		 * optimising this loop into a modulo operation. See
  		 * also __iter_div_u64_rem() in include/linux/time.h
  		 */
  		asm("" : "+rm"(nsec));

  		nsec -= NSEC_PER_SEC;
  		++sec;
  	}
  	while (nsec < 0) {

  		asm("" : "+rm"(nsec));

  		nsec += NSEC_PER_SEC;
  		--sec;
  	}
  	ts->tv_sec = sec;
  	ts->tv_nsec = nsec;
  }

  EXPORT_SYMBOL(set_normalized_timespec);

  /**
   * ns_to_timespec - Convert nanoseconds to timespec
   * @nsec:       the nanoseconds value to be converted
   *
   * Returns the timespec representation of the nsec parameter.
   */

  struct timespec ns_to_timespec(const s64 nsec)

  {
  	struct timespec ts;

  	s32 rem;

  	if (!nsec)
  		return (struct timespec) {0, 0};

  	ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
  	if (unlikely(rem < 0)) {
  		ts.tv_sec--;
  		rem += NSEC_PER_SEC;
  	}
  	ts.tv_nsec = rem;

  
  	return ts;
  }

  EXPORT_SYMBOL(ns_to_timespec);

  
  /**
   * ns_to_timeval - Convert nanoseconds to timeval
   * @nsec:       the nanoseconds value to be converted
   *
   * Returns the timeval representation of the nsec parameter.
   */

  struct timeval ns_to_timeval(const s64 nsec)

  {
  	struct timespec ts = ns_to_timespec(nsec);
  	struct timeval tv;
  
  	tv.tv_sec = ts.tv_sec;
  	tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
  
  	return tv;
  }

  EXPORT_SYMBOL(ns_to_timeval);

  /*

   * When we convert to jiffies then we interpret incoming values
   * the following way:
   *
   * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
   *
   * - 'too large' values [that would result in larger than
   *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
   *
   * - all other values are converted to jiffies by either multiplying
   *   the input value by a factor or dividing it with a factor
   *
   * We must also be careful about 32-bit overflows.
   */

  unsigned long msecs_to_jiffies(const unsigned int m)
  {

  	/*
  	 * Negative value, means infinite timeout:
  	 */
  	if ((int)m < 0)

  		return MAX_JIFFY_OFFSET;

  #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)

  	/*
  	 * HZ is equal to or smaller than 1000, and 1000 is a nice
  	 * round multiple of HZ, divide with the factor between them,
  	 * but round upwards:
  	 */

  	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
  #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)

  	/*
  	 * HZ is larger than 1000, and HZ is a nice round multiple of
  	 * 1000 - simply multiply with the factor between them.
  	 *
  	 * But first make sure the multiplication result cannot
  	 * overflow:
  	 */
  	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
  		return MAX_JIFFY_OFFSET;

  	return m * (HZ / MSEC_PER_SEC);
  #else

  	/*
  	 * Generic case - multiply, round and divide. But first
  	 * check that if we are doing a net multiplication, that

  	 * we wouldn't overflow:

  	 */
  	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
  		return MAX_JIFFY_OFFSET;

  	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)

  		>> MSEC_TO_HZ_SHR32;

  #endif
  }
  EXPORT_SYMBOL(msecs_to_jiffies);
  
  unsigned long usecs_to_jiffies(const unsigned int u)
  {
  	if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
  		return MAX_JIFFY_OFFSET;
  #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
  	return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
  #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
  	return u * (HZ / USEC_PER_SEC);
  #else

  	return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)

  		>> USEC_TO_HZ_SHR32;

  #endif
  }
  EXPORT_SYMBOL(usecs_to_jiffies);
  
  /*
   * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
   * that a remainder subtract here would not do the right thing as the
   * resolution values don't fall on second boundries.  I.e. the line:
   * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
   *
   * Rather, we just shift the bits off the right.
   *
   * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
   * value to a scaled second value.
   */
  unsigned long
  timespec_to_jiffies(const struct timespec *value)
  {
  	unsigned long sec = value->tv_sec;
  	long nsec = value->tv_nsec + TICK_NSEC - 1;
  
  	if (sec >= MAX_SEC_IN_JIFFIES){
  		sec = MAX_SEC_IN_JIFFIES;
  		nsec = 0;
  	}
  	return (((u64)sec * SEC_CONVERSION) +
  		(((u64)nsec * NSEC_CONVERSION) >>
  		 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
  
  }
  EXPORT_SYMBOL(timespec_to_jiffies);
  
  void
  jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
  {
  	/*
  	 * Convert jiffies to nanoseconds and separate with
  	 * one divide.
  	 */

  	u32 rem;
  	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
  				    NSEC_PER_SEC, &rem);
  	value->tv_nsec = rem;

  }
  EXPORT_SYMBOL(jiffies_to_timespec);
  
  /* Same for "timeval"
   *
   * Well, almost.  The problem here is that the real system resolution is
   * in nanoseconds and the value being converted is in micro seconds.
   * Also for some machines (those that use HZ = 1024, in-particular),
   * there is a LARGE error in the tick size in microseconds.
  
   * The solution we use is to do the rounding AFTER we convert the
   * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
   * Instruction wise, this should cost only an additional add with carry
   * instruction above the way it was done above.
   */
  unsigned long
  timeval_to_jiffies(const struct timeval *value)
  {
  	unsigned long sec = value->tv_sec;
  	long usec = value->tv_usec;
  
  	if (sec >= MAX_SEC_IN_JIFFIES){
  		sec = MAX_SEC_IN_JIFFIES;
  		usec = 0;
  	}
  	return (((u64)sec * SEC_CONVERSION) +
  		(((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
  		 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
  }

  EXPORT_SYMBOL(timeval_to_jiffies);

  
  void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
  {
  	/*
  	 * Convert jiffies to nanoseconds and separate with
  	 * one divide.
  	 */

  	u32 rem;

  	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
  				    NSEC_PER_SEC, &rem);
  	value->tv_usec = rem / NSEC_PER_USEC;

  }

  EXPORT_SYMBOL(jiffies_to_timeval);

  
  /*
   * Convert jiffies/jiffies_64 to clock_t and back.
   */

  clock_t jiffies_to_clock_t(unsigned long x)

  {
  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0

  # if HZ < USER_HZ
  	return x * (USER_HZ / HZ);
  # else

  	return x / (HZ / USER_HZ);

  # endif

  #else

  	return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);

  #endif
  }
  EXPORT_SYMBOL(jiffies_to_clock_t);
  
  unsigned long clock_t_to_jiffies(unsigned long x)
  {
  #if (HZ % USER_HZ)==0
  	if (x >= ~0UL / (HZ / USER_HZ))
  		return ~0UL;
  	return x * (HZ / USER_HZ);
  #else

  	/* Don't worry about loss of precision here .. */
  	if (x >= ~0UL / HZ * USER_HZ)
  		return ~0UL;
  
  	/* .. but do try to contain it here */

  	return div_u64((u64)x * HZ, USER_HZ);

  #endif
  }
  EXPORT_SYMBOL(clock_t_to_jiffies);
  
  u64 jiffies_64_to_clock_t(u64 x)
  {
  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0

  # if HZ < USER_HZ

  	x = div_u64(x * USER_HZ, HZ);

  # elif HZ > USER_HZ

  	x = div_u64(x, HZ / USER_HZ);

  # else
  	/* Nothing to do */

  # endif

  #else
  	/*
  	 * There are better ways that don't overflow early,
  	 * but even this doesn't overflow in hundreds of years
  	 * in 64 bits, so..
  	 */

  	x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));

  #endif
  	return x;
  }

  EXPORT_SYMBOL(jiffies_64_to_clock_t);
  
  u64 nsec_to_clock_t(u64 x)
  {
  #if (NSEC_PER_SEC % USER_HZ) == 0

  	return div_u64(x, NSEC_PER_SEC / USER_HZ);

  #elif (USER_HZ % 512) == 0

  	return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);

  #else
  	/*
           * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
           * overflow after 64.99 years.
           * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
           */

  	return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);

  #endif

  }

  /**

   * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64

   *
   * @n:	nsecs in u64
   *
   * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
   * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
   * for scheduler, not for use in device drivers to calculate timeout value.
   *
   * note:
   *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
   *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
   */

  u64 nsecs_to_jiffies64(u64 n)

  {
  #if (NSEC_PER_SEC % HZ) == 0
  	/* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
  	return div_u64(n, NSEC_PER_SEC / HZ);
  #elif (HZ % 512) == 0
  	/* overflow after 292 years if HZ = 1024 */
  	return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
  #else
  	/*
  	 * Generic case - optimized for cases where HZ is a multiple of 3.
  	 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
  	 */
  	return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
  #endif
  }

  /**
   * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
   *
   * @n:	nsecs in u64
   *
   * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
   * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
   * for scheduler, not for use in device drivers to calculate timeout value.
   *
   * note:
   *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
   *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
   */
  unsigned long nsecs_to_jiffies(u64 n)
  {
  	return (unsigned long)nsecs_to_jiffies64(n);
  }

  /*
   * Add two timespec values and do a safety check for overflow.
   * It's assumed that both values are valid (>= 0)
   */
  struct timespec timespec_add_safe(const struct timespec lhs,
  				  const struct timespec rhs)
  {
  	struct timespec res;
  
  	set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
  				lhs.tv_nsec + rhs.tv_nsec);
  
  	if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
  		res.tv_sec = TIME_T_MAX;
  
  	return res;
  }