linux/kernel/time.c
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   1/*
   2 *  linux/kernel/time.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *
   6 *  This file contains the interface functions for the various
   7 *  time related system calls: time, stime, gettimeofday, settimeofday,
   8 *                             adjtime
   9 */
  10/*
  11 * Modification history kernel/time.c
  12 *
  13 * 1993-09-02    Philip Gladstone
  14 *      Created file with time related functions from sched.c and adjtimex()
  15 * 1993-10-08    Torsten Duwe
  16 *      adjtime interface update and CMOS clock write code
  17 * 1995-08-13    Torsten Duwe
  18 *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
  19 * 1999-01-16    Ulrich Windl
  20 *      Introduced error checking for many cases in adjtimex().
  21 *      Updated NTP code according to technical memorandum Jan '96
  22 *      "A Kernel Model for Precision Timekeeping" by Dave Mills
  23 *      Allow time_constant larger than MAXTC(6) for NTP v4 (MAXTC == 10)
  24 *      (Even though the technical memorandum forbids it)
  25 * 2004-07-14    Christoph Lameter
  26 *      Added getnstimeofday to allow the posix timer functions to return
  27 *      with nanosecond accuracy
  28 */
  29
  30#include <linux/module.h>
  31#include <linux/timex.h>
  32#include <linux/capability.h>
  33#include <linux/clocksource.h>
  34#include <linux/errno.h>
  35#include <linux/syscalls.h>
  36#include <linux/security.h>
  37#include <linux/fs.h>
  38#include <linux/slab.h>
  39#include <linux/math64.h>
  40
  41#include <asm/uaccess.h>
  42#include <asm/unistd.h>
  43
  44#include "timeconst.h"
  45
  46/*
  47 * The timezone where the local system is located.  Used as a default by some
  48 * programs who obtain this value by using gettimeofday.
  49 */
  50struct timezone sys_tz;
  51
  52EXPORT_SYMBOL(sys_tz);
  53
  54#ifdef __ARCH_WANT_SYS_TIME
  55
  56/*
  57 * sys_time() can be implemented in user-level using
  58 * sys_gettimeofday().  Is this for backwards compatibility?  If so,
  59 * why not move it into the appropriate arch directory (for those
  60 * architectures that need it).
  61 */
  62asmlinkage long sys_time(time_t __user * tloc)
  63{
  64        time_t i = get_seconds();
  65
  66        if (tloc) {
  67                if (put_user(i,tloc))
  68                        i = -EFAULT;
  69        }
  70        return i;
  71}
  72
  73/*
  74 * sys_stime() can be implemented in user-level using
  75 * sys_settimeofday().  Is this for backwards compatibility?  If so,
  76 * why not move it into the appropriate arch directory (for those
  77 * architectures that need it).
  78 */
  79
  80asmlinkage long sys_stime(time_t __user *tptr)
  81{
  82        struct timespec tv;
  83        int err;
  84
  85        if (get_user(tv.tv_sec, tptr))
  86                return -EFAULT;
  87
  88        tv.tv_nsec = 0;
  89
  90        err = security_settime(&tv, NULL);
  91        if (err)
  92                return err;
  93
  94        do_settimeofday(&tv);
  95        return 0;
  96}
  97
  98#endif /* __ARCH_WANT_SYS_TIME */
  99
 100asmlinkage long sys_gettimeofday(struct timeval __user *tv,
 101                                 struct timezone __user *tz)
 102{
 103        if (likely(tv != NULL)) {
 104                struct timeval ktv;
 105                do_gettimeofday(&ktv);
 106                if (copy_to_user(tv, &ktv, sizeof(ktv)))
 107                        return -EFAULT;
 108        }
 109        if (unlikely(tz != NULL)) {
 110                if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
 111                        return -EFAULT;
 112        }
 113        return 0;
 114}
 115
 116/*
 117 * Adjust the time obtained from the CMOS to be UTC time instead of
 118 * local time.
 119 *
 120 * This is ugly, but preferable to the alternatives.  Otherwise we
 121 * would either need to write a program to do it in /etc/rc (and risk
 122 * confusion if the program gets run more than once; it would also be
 123 * hard to make the program warp the clock precisely n hours)  or
 124 * compile in the timezone information into the kernel.  Bad, bad....
 125 *
 126 *                                              - TYT, 1992-01-01
 127 *
 128 * The best thing to do is to keep the CMOS clock in universal time (UTC)
 129 * as real UNIX machines always do it. This avoids all headaches about
 130 * daylight saving times and warping kernel clocks.
 131 */
 132static inline void warp_clock(void)
 133{
 134        write_seqlock_irq(&xtime_lock);
 135        wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
 136        xtime.tv_sec += sys_tz.tz_minuteswest * 60;
 137        update_xtime_cache(0);
 138        write_sequnlock_irq(&xtime_lock);
 139        clock_was_set();
 140}
 141
 142/*
 143 * In case for some reason the CMOS clock has not already been running
 144 * in UTC, but in some local time: The first time we set the timezone,
 145 * we will warp the clock so that it is ticking UTC time instead of
 146 * local time. Presumably, if someone is setting the timezone then we
 147 * are running in an environment where the programs understand about
 148 * timezones. This should be done at boot time in the /etc/rc script,
 149 * as soon as possible, so that the clock can be set right. Otherwise,
 150 * various programs will get confused when the clock gets warped.
 151 */
 152
 153int do_sys_settimeofday(struct timespec *tv, struct timezone *tz)
 154{
 155        static int firsttime = 1;
 156        int error = 0;
 157
 158        if (tv && !timespec_valid(tv))
 159                return -EINVAL;
 160
 161        error = security_settime(tv, tz);
 162        if (error)
 163                return error;
 164
 165        if (tz) {
 166                /* SMP safe, global irq locking makes it work. */
 167                sys_tz = *tz;
 168                update_vsyscall_tz();
 169                if (firsttime) {
 170                        firsttime = 0;
 171                        if (!tv)
 172                                warp_clock();
 173                }
 174        }
 175        if (tv)
 176        {
 177                /* SMP safe, again the code in arch/foo/time.c should
 178                 * globally block out interrupts when it runs.
 179                 */
 180                return do_settimeofday(tv);
 181        }
 182        return 0;
 183}
 184
 185asmlinkage long sys_settimeofday(struct timeval __user *tv,
 186                                struct timezone __user *tz)
 187{
 188        struct timeval user_tv;
 189        struct timespec new_ts;
 190        struct timezone new_tz;
 191
 192        if (tv) {
 193                if (copy_from_user(&user_tv, tv, sizeof(*tv)))
 194                        return -EFAULT;
 195                new_ts.tv_sec = user_tv.tv_sec;
 196                new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
 197        }
 198        if (tz) {
 199                if (copy_from_user(&new_tz, tz, sizeof(*tz)))
 200                        return -EFAULT;
 201        }
 202
 203        return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
 204}
 205
 206asmlinkage long sys_adjtimex(struct timex __user *txc_p)
 207{
 208        struct timex txc;               /* Local copy of parameter */
 209        int ret;
 210
 211        /* Copy the user data space into the kernel copy
 212         * structure. But bear in mind that the structures
 213         * may change
 214         */
 215        if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
 216                return -EFAULT;
 217        ret = do_adjtimex(&txc);
 218        return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
 219}
 220
 221/**
 222 * current_fs_time - Return FS time
 223 * @sb: Superblock.
 224 *
 225 * Return the current time truncated to the time granularity supported by
 226 * the fs.
 227 */
 228struct timespec current_fs_time(struct super_block *sb)
 229{
 230        struct timespec now = current_kernel_time();
 231        return timespec_trunc(now, sb->s_time_gran);
 232}
 233EXPORT_SYMBOL(current_fs_time);
 234
 235/*
 236 * Convert jiffies to milliseconds and back.
 237 *
 238 * Avoid unnecessary multiplications/divisions in the
 239 * two most common HZ cases:
 240 */
 241unsigned int inline jiffies_to_msecs(const unsigned long j)
 242{
 243#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 244        return (MSEC_PER_SEC / HZ) * j;
 245#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 246        return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
 247#else
 248# if BITS_PER_LONG == 32
 249        return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
 250# else
 251        return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
 252# endif
 253#endif
 254}
 255EXPORT_SYMBOL(jiffies_to_msecs);
 256
 257unsigned int inline jiffies_to_usecs(const unsigned long j)
 258{
 259#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 260        return (USEC_PER_SEC / HZ) * j;
 261#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 262        return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
 263#else
 264# if BITS_PER_LONG == 32
 265        return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
 266# else
 267        return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
 268# endif
 269#endif
 270}
 271EXPORT_SYMBOL(jiffies_to_usecs);
 272
 273/**
 274 * timespec_trunc - Truncate timespec to a granularity
 275 * @t: Timespec
 276 * @gran: Granularity in ns.
 277 *
 278 * Truncate a timespec to a granularity. gran must be smaller than a second.
 279 * Always rounds down.
 280 *
 281 * This function should be only used for timestamps returned by
 282 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
 283 * it doesn't handle the better resolution of the latter.
 284 */
 285struct timespec timespec_trunc(struct timespec t, unsigned gran)
 286{
 287        /*
 288         * Division is pretty slow so avoid it for common cases.
 289         * Currently current_kernel_time() never returns better than
 290         * jiffies resolution. Exploit that.
 291         */
 292        if (gran <= jiffies_to_usecs(1) * 1000) {
 293                /* nothing */
 294        } else if (gran == 1000000000) {
 295                t.tv_nsec = 0;
 296        } else {
 297                t.tv_nsec -= t.tv_nsec % gran;
 298        }
 299        return t;
 300}
 301EXPORT_SYMBOL(timespec_trunc);
 302
 303#ifndef CONFIG_GENERIC_TIME
 304/*
 305 * Simulate gettimeofday using do_gettimeofday which only allows a timeval
 306 * and therefore only yields usec accuracy
 307 */
 308void getnstimeofday(struct timespec *tv)
 309{
 310        struct timeval x;
 311
 312        do_gettimeofday(&x);
 313        tv->tv_sec = x.tv_sec;
 314        tv->tv_nsec = x.tv_usec * NSEC_PER_USEC;
 315}
 316EXPORT_SYMBOL_GPL(getnstimeofday);
 317#endif
 318
 319/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 320 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 321 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 322 *
 323 * [For the Julian calendar (which was used in Russia before 1917,
 324 * Britain & colonies before 1752, anywhere else before 1582,
 325 * and is still in use by some communities) leave out the
 326 * -year/100+year/400 terms, and add 10.]
 327 *
 328 * This algorithm was first published by Gauss (I think).
 329 *
 330 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 331 * machines where long is 32-bit! (However, as time_t is signed, we
 332 * will already get problems at other places on 2038-01-19 03:14:08)
 333 */
 334unsigned long
 335mktime(const unsigned int year0, const unsigned int mon0,
 336       const unsigned int day, const unsigned int hour,
 337       const unsigned int min, const unsigned int sec)
 338{
 339        unsigned int mon = mon0, year = year0;
 340
 341        /* 1..12 -> 11,12,1..10 */
 342        if (0 >= (int) (mon -= 2)) {
 343                mon += 12;      /* Puts Feb last since it has leap day */
 344                year -= 1;
 345        }
 346
 347        return ((((unsigned long)
 348                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
 349                  year*365 - 719499
 350            )*24 + hour /* now have hours */
 351          )*60 + min /* now have minutes */
 352        )*60 + sec; /* finally seconds */
 353}
 354
 355EXPORT_SYMBOL(mktime);
 356
 357/**
 358 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 359 *
 360 * @ts:         pointer to timespec variable to be set
 361 * @sec:        seconds to set
 362 * @nsec:       nanoseconds to set
 363 *
 364 * Set seconds and nanoseconds field of a timespec variable and
 365 * normalize to the timespec storage format
 366 *
 367 * Note: The tv_nsec part is always in the range of
 368 *      0 <= tv_nsec < NSEC_PER_SEC
 369 * For negative values only the tv_sec field is negative !
 370 */
 371void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
 372{
 373        while (nsec >= NSEC_PER_SEC) {
 374                nsec -= NSEC_PER_SEC;
 375                ++sec;
 376        }
 377        while (nsec < 0) {
 378                nsec += NSEC_PER_SEC;
 379                --sec;
 380        }
 381        ts->tv_sec = sec;
 382        ts->tv_nsec = nsec;
 383}
 384EXPORT_SYMBOL(set_normalized_timespec);
 385
 386/**
 387 * ns_to_timespec - Convert nanoseconds to timespec
 388 * @nsec:       the nanoseconds value to be converted
 389 *
 390 * Returns the timespec representation of the nsec parameter.
 391 */
 392struct timespec ns_to_timespec(const s64 nsec)
 393{
 394        struct timespec ts;
 395        s32 rem;
 396
 397        if (!nsec)
 398                return (struct timespec) {0, 0};
 399
 400        ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
 401        if (unlikely(rem < 0)) {
 402                ts.tv_sec--;
 403                rem += NSEC_PER_SEC;
 404        }
 405        ts.tv_nsec = rem;
 406
 407        return ts;
 408}
 409EXPORT_SYMBOL(ns_to_timespec);
 410
 411/**
 412 * ns_to_timeval - Convert nanoseconds to timeval
 413 * @nsec:       the nanoseconds value to be converted
 414 *
 415 * Returns the timeval representation of the nsec parameter.
 416 */
 417struct timeval ns_to_timeval(const s64 nsec)
 418{
 419        struct timespec ts = ns_to_timespec(nsec);
 420        struct timeval tv;
 421
 422        tv.tv_sec = ts.tv_sec;
 423        tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
 424
 425        return tv;
 426}
 427EXPORT_SYMBOL(ns_to_timeval);
 428
 429/*
 430 * When we convert to jiffies then we interpret incoming values
 431 * the following way:
 432 *
 433 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 434 *
 435 * - 'too large' values [that would result in larger than
 436 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 437 *
 438 * - all other values are converted to jiffies by either multiplying
 439 *   the input value by a factor or dividing it with a factor
 440 *
 441 * We must also be careful about 32-bit overflows.
 442 */
 443unsigned long msecs_to_jiffies(const unsigned int m)
 444{
 445        /*
 446         * Negative value, means infinite timeout:
 447         */
 448        if ((int)m < 0)
 449                return MAX_JIFFY_OFFSET;
 450
 451#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 452        /*
 453         * HZ is equal to or smaller than 1000, and 1000 is a nice
 454         * round multiple of HZ, divide with the factor between them,
 455         * but round upwards:
 456         */
 457        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
 458#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 459        /*
 460         * HZ is larger than 1000, and HZ is a nice round multiple of
 461         * 1000 - simply multiply with the factor between them.
 462         *
 463         * But first make sure the multiplication result cannot
 464         * overflow:
 465         */
 466        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 467                return MAX_JIFFY_OFFSET;
 468
 469        return m * (HZ / MSEC_PER_SEC);
 470#else
 471        /*
 472         * Generic case - multiply, round and divide. But first
 473         * check that if we are doing a net multiplication, that
 474         * we wouldn't overflow:
 475         */
 476        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 477                return MAX_JIFFY_OFFSET;
 478
 479        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 480                >> MSEC_TO_HZ_SHR32;
 481#endif
 482}
 483EXPORT_SYMBOL(msecs_to_jiffies);
 484
 485unsigned long usecs_to_jiffies(const unsigned int u)
 486{
 487        if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
 488                return MAX_JIFFY_OFFSET;
 489#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 490        return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
 491#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 492        return u * (HZ / USEC_PER_SEC);
 493#else
 494        return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
 495                >> USEC_TO_HZ_SHR32;
 496#endif
 497}
 498EXPORT_SYMBOL(usecs_to_jiffies);
 499
 500/*
 501 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 502 * that a remainder subtract here would not do the right thing as the
 503 * resolution values don't fall on second boundries.  I.e. the line:
 504 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 505 *
 506 * Rather, we just shift the bits off the right.
 507 *
 508 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 509 * value to a scaled second value.
 510 */
 511unsigned long
 512timespec_to_jiffies(const struct timespec *value)
 513{
 514        unsigned long sec = value->tv_sec;
 515        long nsec = value->tv_nsec + TICK_NSEC - 1;
 516
 517        if (sec >= MAX_SEC_IN_JIFFIES){
 518                sec = MAX_SEC_IN_JIFFIES;
 519                nsec = 0;
 520        }
 521        return (((u64)sec * SEC_CONVERSION) +
 522                (((u64)nsec * NSEC_CONVERSION) >>
 523                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 524
 525}
 526EXPORT_SYMBOL(timespec_to_jiffies);
 527
 528void
 529jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
 530{
 531        /*
 532         * Convert jiffies to nanoseconds and separate with
 533         * one divide.
 534         */
 535        u32 rem;
 536        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 537                                    NSEC_PER_SEC, &rem);
 538        value->tv_nsec = rem;
 539}
 540EXPORT_SYMBOL(jiffies_to_timespec);
 541
 542/* Same for "timeval"
 543 *
 544 * Well, almost.  The problem here is that the real system resolution is
 545 * in nanoseconds and the value being converted is in micro seconds.
 546 * Also for some machines (those that use HZ = 1024, in-particular),
 547 * there is a LARGE error in the tick size in microseconds.
 548
 549 * The solution we use is to do the rounding AFTER we convert the
 550 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 551 * Instruction wise, this should cost only an additional add with carry
 552 * instruction above the way it was done above.
 553 */
 554unsigned long
 555timeval_to_jiffies(const struct timeval *value)
 556{
 557        unsigned long sec = value->tv_sec;
 558        long usec = value->tv_usec;
 559
 560        if (sec >= MAX_SEC_IN_JIFFIES){
 561                sec = MAX_SEC_IN_JIFFIES;
 562                usec = 0;
 563        }
 564        return (((u64)sec * SEC_CONVERSION) +
 565                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
 566                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 567}
 568EXPORT_SYMBOL(timeval_to_jiffies);
 569
 570void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
 571{
 572        /*
 573         * Convert jiffies to nanoseconds and separate with
 574         * one divide.
 575         */
 576        u32 rem;
 577
 578        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 579                                    NSEC_PER_SEC, &rem);
 580        value->tv_usec = rem / NSEC_PER_USEC;
 581}
 582EXPORT_SYMBOL(jiffies_to_timeval);
 583
 584/*
 585 * Convert jiffies/jiffies_64 to clock_t and back.
 586 */
 587clock_t jiffies_to_clock_t(long x)
 588{
 589#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 590# if HZ < USER_HZ
 591        return x * (USER_HZ / HZ);
 592# else
 593        return x / (HZ / USER_HZ);
 594# endif
 595#else
 596        return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
 597#endif
 598}
 599EXPORT_SYMBOL(jiffies_to_clock_t);
 600
 601unsigned long clock_t_to_jiffies(unsigned long x)
 602{
 603#if (HZ % USER_HZ)==0
 604        if (x >= ~0UL / (HZ / USER_HZ))
 605                return ~0UL;
 606        return x * (HZ / USER_HZ);
 607#else
 608        /* Don't worry about loss of precision here .. */
 609        if (x >= ~0UL / HZ * USER_HZ)
 610                return ~0UL;
 611
 612        /* .. but do try to contain it here */
 613        return div_u64((u64)x * HZ, USER_HZ);
 614#endif
 615}
 616EXPORT_SYMBOL(clock_t_to_jiffies);
 617
 618u64 jiffies_64_to_clock_t(u64 x)
 619{
 620#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 621# if HZ < USER_HZ
 622        x = div_u64(x * USER_HZ, HZ);
 623# elif HZ > USER_HZ
 624        x = div_u64(x, HZ / USER_HZ);
 625# else
 626        /* Nothing to do */
 627# endif
 628#else
 629        /*
 630         * There are better ways that don't overflow early,
 631         * but even this doesn't overflow in hundreds of years
 632         * in 64 bits, so..
 633         */
 634        x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 635#endif
 636        return x;
 637}
 638EXPORT_SYMBOL(jiffies_64_to_clock_t);
 639
 640u64 nsec_to_clock_t(u64 x)
 641{
 642#if (NSEC_PER_SEC % USER_HZ) == 0
 643        return div_u64(x, NSEC_PER_SEC / USER_HZ);
 644#elif (USER_HZ % 512) == 0
 645        return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
 646#else
 647        /*
 648         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
 649         * overflow after 64.99 years.
 650         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
 651         */
 652        return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
 653#endif
 654}
 655
 656#if (BITS_PER_LONG < 64)
 657u64 get_jiffies_64(void)
 658{
 659        unsigned long seq;
 660        u64 ret;
 661
 662        do {
 663                seq = read_seqbegin(&xtime_lock);
 664                ret = jiffies_64;
 665        } while (read_seqretry(&xtime_lock, seq));
 666        return ret;
 667}
 668EXPORT_SYMBOL(get_jiffies_64);
 669#endif
 670
 671EXPORT_SYMBOL(jiffies);
 672
 673/*
 674 * Add two timespec values and do a safety check for overflow.
 675 * It's assumed that both values are valid (>= 0)
 676 */
 677struct timespec timespec_add_safe(const struct timespec lhs,
 678                                  const struct timespec rhs)
 679{
 680        struct timespec res;
 681
 682        set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
 683                                lhs.tv_nsec + rhs.tv_nsec);
 684
 685        if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
 686                res.tv_sec = TIME_T_MAX;
 687
 688        return res;
 689}
 690
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