/*
 *  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/core.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/timekeeper_internal.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 <generated/timeconst.h>
#include "timekeeping.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;
}

/*
 * Indicates if there is an offset between the system clock and the hardware
 * clock/persistent clock/rtc.
 */
int persistent_clock_is_local;

/*
 * 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)
{
        if (sys_tz.tz_minuteswest != 0) {
                struct timespec adjust;

                persistent_clock_is_local = 1;
                adjust.tv_sec = sys_tz.tz_minuteswest * 60;
                adjust.tv_nsec = 0;
                timekeeping_inject_offset(&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_settimeofday64(const struct timespec64 *tv, const struct timezone *tz)
{
        static int firsttime = 1;
        int error = 0;

        if (tv && !timespec64_valid(tv))
                return -EINVAL;

        error = security_settime64(tv, tz);
        if (error)
                return error;

        if (tz) {
                /* Verify we're witin the +-15 hrs range */
                if (tz->tz_minuteswest > 15*60 || tz->tz_minuteswest < -15*60)
                        return -EINVAL;

                sys_tz = *tz;
                update_vsyscall_tz();
                if (firsttime) {
                        firsttime = 0;
                        if (!tv)
                                warp_clock();
                }
        }
        if (tv)
                return do_settimeofday64(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;

                if (!timeval_valid(&user_tv))
                        return -EINVAL;

                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:
 */
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);

unsigned int jiffies_to_usecs(const unsigned long j)
{
        /*
         * Hz usually doesn't go much further MSEC_PER_SEC.
         * jiffies_to_usecs() and usecs_to_jiffies() depend on that.
         */
        BUILD_BUG_ON(HZ > USEC_PER_SEC);

#if !(USEC_PER_SEC % HZ)
        return (USEC_PER_SEC / HZ) * j;
#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. Always rounds down. gran must
 * not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns).
 */
struct timespec timespec_trunc(struct timespec t, unsigned gran)
{
        /* Avoid division in the common cases 1 ns and 1 s. */
        if (gran == 1) {
                /* nothing */
        } else if (gran == NSEC_PER_SEC) {
                t.tv_nsec = 0;
        } else if (gran > 1 && gran < NSEC_PER_SEC) {
                t.tv_nsec -= t.tv_nsec % gran;
        } else {
                WARN(1, "illegal file time granularity: %u", gran);
        }
        return t;
}
EXPORT_SYMBOL(timespec_trunc);

/*
 * mktime64 - Converts date to seconds.
 * 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).
 *
 * A leap second can be indicated by calling this function with sec as
 * 60 (allowable under ISO 8601).  The leap second is treated the same
 * as the following second since they don't exist in UNIX time.
 *
 * An encoding of midnight at the end of the day as 24:00:00 - ie. midnight
 * tomorrow - (allowable under ISO 8601) is supported.
 */
time64_t mktime64(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 ((((time64_t)
                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
                  year*365 - 719499
            )*24 + hour /* now have hours - midnight tomorrow handled here */
          )*60 + min /* now have minutes */
        )*60 + sec; /* finally seconds */
}
EXPORT_SYMBOL(mktime64);

/**
 * 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);

#if BITS_PER_LONG == 32
/**
 * 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_timespec64(struct timespec64 *ts, time64_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_timespec64);

/**
 * ns_to_timespec64 - Convert nanoseconds to timespec64
 * @nsec:       the nanoseconds value to be converted
 *
 * Returns the timespec64 representation of the nsec parameter.
 */
struct timespec64 ns_to_timespec64(const s64 nsec)
{
        struct timespec64 ts;
        s32 rem;

        if (!nsec)
                return (struct timespec64) {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_timespec64);
#endif
/**
 * msecs_to_jiffies: - convert milliseconds to jiffies
 * @m:  time in milliseconds
 *
 * conversion is done as follows:
 *
 * - 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 and
 *   handling any 32-bit overflows.
 *   for the details see __msecs_to_jiffies()
 *
 * msecs_to_jiffies() checks for the passed in value being a constant
 * via __builtin_constant_p() allowing gcc to eliminate most of the
 * code, __msecs_to_jiffies() is called if the value passed does not
 * allow constant folding and the actual conversion must be done at
 * runtime.
 * the _msecs_to_jiffies helpers are the HZ dependent conversion
 * routines found in include/linux/jiffies.h
 */
unsigned long __msecs_to_jiffies(const unsigned int m)
{
        /*
         * Negative value, means infinite timeout:
         */
        if ((int)m < 0)
                return MAX_JIFFY_OFFSET;
        return _msecs_to_jiffies(m);
}
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;
        return _usecs_to_jiffies(u);
}
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.
 * Note that due to the small error in the multiplier here, this
 * rounding is incorrect for sufficiently large values of tv_nsec, but
 * well formed timespecs should have tv_nsec < NSEC_PER_SEC, so we're
 * OK.
 *
 * 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.
 */
static unsigned long
__timespec64_to_jiffies(u64 sec, long nsec)
{
        nsec = nsec + TICK_NSEC - 1;

        if (sec >= MAX_SEC_IN_JIFFIES){
                sec = MAX_SEC_IN_JIFFIES;
                nsec = 0;
        }
        return ((sec * SEC_CONVERSION) +
                (((u64)nsec * NSEC_CONVERSION) >>
                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;

}

static unsigned long
__timespec_to_jiffies(unsigned long sec, long nsec)
{
        return __timespec64_to_jiffies((u64)sec, nsec);
}

unsigned long
timespec64_to_jiffies(const struct timespec64 *value)
{
        return __timespec64_to_jiffies(value->tv_sec, value->tv_nsec);
}
EXPORT_SYMBOL(timespec64_to_jiffies);

void
jiffies_to_timespec64(const unsigned long jiffies, struct timespec64 *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_timespec64);

/*
 * We could use a similar algorithm to timespec_to_jiffies (with a
 * different multiplier for usec instead of nsec). But this has a
 * problem with rounding: we can't exactly add TICK_NSEC - 1 to the
 * usec value, since it's not necessarily integral.
 *
 * We could instead round in the intermediate scaled representation
 * (i.e. in units of 1/2^(large scale) jiffies) but that's also
 * perilous: the scaling introduces a small positive error, which
 * combined with a division-rounding-upward (i.e. adding 2^(scale) - 1
 * units to the intermediate before shifting) leads to accidental
 * overflow and overestimates.
 *
 * At the cost of one additional multiplication by a constant, just
 * use the timespec implementation.
 */
unsigned long
timeval_to_jiffies(const struct timeval *value)
{
        return __timespec_to_jiffies(value->tv_sec,
                                     value->tv_usec * NSEC_PER_USEC);
}
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
}
EXPORT_SYMBOL(nsecs_to_jiffies64);

/**
 * 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);
}
EXPORT_SYMBOL_GPL(nsecs_to_jiffies);

/*
 * 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;
}

/*
 * Add two timespec64 values and do a safety check for overflow.
 * It's assumed that both values are valid (>= 0).
 * And, each timespec64 is in normalized form.
 */
struct timespec64 timespec64_add_safe(const struct timespec64 lhs,
                                const struct timespec64 rhs)
{
        struct timespec64 res;

        set_normalized_timespec64(&res, lhs.tv_sec + rhs.tv_sec,
                        lhs.tv_nsec + rhs.tv_nsec);

        if (unlikely(res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)) {
                res.tv_sec = TIME64_MAX;
                res.tv_nsec = 0;
        }

        return res;
}