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/export.h>
  31#include <linux/timex.h>
  32#include <linux/capability.h>
  33#include <linux/timekeeper_internal.h>
  34#include <linux/errno.h>
  35#include <linux/syscalls.h>
  36#include <linux/security.h>
  37#include <linux/fs.h>
  38#include <linux/math64.h>
  39#include <linux/ptrace.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 */
  62SYSCALL_DEFINE1(time, time_t __user *, tloc)
  63{
  64        time_t i = get_seconds();
  65
  66        if (tloc) {
  67                if (put_user(i,tloc))
  68                        return -EFAULT;
  69        }
  70        force_successful_syscall_return();
  71        return i;
  72}
  73
  74/*
  75 * sys_stime() can be implemented in user-level using
  76 * sys_settimeofday().  Is this for backwards compatibility?  If so,
  77 * why not move it into the appropriate arch directory (for those
  78 * architectures that need it).
  79 */
  80
  81SYSCALL_DEFINE1(stime, time_t __user *, tptr)
  82{
  83        struct timespec tv;
  84        int err;
  85
  86        if (get_user(tv.tv_sec, tptr))
  87                return -EFAULT;
  88
  89        tv.tv_nsec = 0;
  90
  91        err = security_settime(&tv, NULL);
  92        if (err)
  93                return err;
  94
  95        do_settimeofday(&tv);
  96        return 0;
  97}
  98
  99#endif /* __ARCH_WANT_SYS_TIME */
 100
 101SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
 102                struct timezone __user *, tz)
 103{
 104        if (likely(tv != NULL)) {
 105                struct timeval ktv;
 106                do_gettimeofday(&ktv);
 107                if (copy_to_user(tv, &ktv, sizeof(ktv)))
 108                        return -EFAULT;
 109        }
 110        if (unlikely(tz != NULL)) {
 111                if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
 112                        return -EFAULT;
 113        }
 114        return 0;
 115}
 116
 117/*
 118 * Indicates if there is an offset between the system clock and the hardware
 119 * clock/persistent clock/rtc.
 120 */
 121int persistent_clock_is_local;
 122
 123/*
 124 * Adjust the time obtained from the CMOS to be UTC time instead of
 125 * local time.
 126 *
 127 * This is ugly, but preferable to the alternatives.  Otherwise we
 128 * would either need to write a program to do it in /etc/rc (and risk
 129 * confusion if the program gets run more than once; it would also be
 130 * hard to make the program warp the clock precisely n hours)  or
 131 * compile in the timezone information into the kernel.  Bad, bad....
 132 *
 133 *                                              - TYT, 1992-01-01
 134 *
 135 * The best thing to do is to keep the CMOS clock in universal time (UTC)
 136 * as real UNIX machines always do it. This avoids all headaches about
 137 * daylight saving times and warping kernel clocks.
 138 */
 139static inline void warp_clock(void)
 140{
 141        struct timespec adjust;
 142
 143        adjust = current_kernel_time();
 144        if (sys_tz.tz_minuteswest != 0)
 145                persistent_clock_is_local = 1;
 146        adjust.tv_sec += sys_tz.tz_minuteswest * 60;
 147        do_settimeofday(&adjust);
 148}
 149
 150/*
 151 * In case for some reason the CMOS clock has not already been running
 152 * in UTC, but in some local time: The first time we set the timezone,
 153 * we will warp the clock so that it is ticking UTC time instead of
 154 * local time. Presumably, if someone is setting the timezone then we
 155 * are running in an environment where the programs understand about
 156 * timezones. This should be done at boot time in the /etc/rc script,
 157 * as soon as possible, so that the clock can be set right. Otherwise,
 158 * various programs will get confused when the clock gets warped.
 159 */
 160
 161int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
 162{
 163        static int firsttime = 1;
 164        int error = 0;
 165
 166        if (tv && !timespec_valid(tv))
 167                return -EINVAL;
 168
 169        error = security_settime(tv, tz);
 170        if (error)
 171                return error;
 172
 173        if (tz) {
 174                sys_tz = *tz;
 175                update_vsyscall_tz();
 176                if (firsttime) {
 177                        firsttime = 0;
 178                        if (!tv)
 179                                warp_clock();
 180                }
 181        }
 182        if (tv)
 183                return do_settimeofday(tv);
 184        return 0;
 185}
 186
 187SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
 188                struct timezone __user *, tz)
 189{
 190        struct timeval user_tv;
 191        struct timespec new_ts;
 192        struct timezone new_tz;
 193
 194        if (tv) {
 195                if (copy_from_user(&user_tv, tv, sizeof(*tv)))
 196                        return -EFAULT;
 197                new_ts.tv_sec = user_tv.tv_sec;
 198                new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
 199        }
 200        if (tz) {
 201                if (copy_from_user(&new_tz, tz, sizeof(*tz)))
 202                        return -EFAULT;
 203        }
 204
 205        return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
 206}
 207
 208SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
 209{
 210        struct timex txc;               /* Local copy of parameter */
 211        int ret;
 212
 213        /* Copy the user data space into the kernel copy
 214         * structure. But bear in mind that the structures
 215         * may change
 216         */
 217        if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
 218                return -EFAULT;
 219        ret = do_adjtimex(&txc);
 220        return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
 221}
 222
 223/**
 224 * current_fs_time - Return FS time
 225 * @sb: Superblock.
 226 *
 227 * Return the current time truncated to the time granularity supported by
 228 * the fs.
 229 */
 230struct timespec current_fs_time(struct super_block *sb)
 231{
 232        struct timespec now = current_kernel_time();
 233        return timespec_trunc(now, sb->s_time_gran);
 234}
 235EXPORT_SYMBOL(current_fs_time);
 236
 237/*
 238 * Convert jiffies to milliseconds and back.
 239 *
 240 * Avoid unnecessary multiplications/divisions in the
 241 * two most common HZ cases:
 242 */
 243unsigned int jiffies_to_msecs(const unsigned long j)
 244{
 245#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 246        return (MSEC_PER_SEC / HZ) * j;
 247#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 248        return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
 249#else
 250# if BITS_PER_LONG == 32
 251        return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
 252# else
 253        return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
 254# endif
 255#endif
 256}
 257EXPORT_SYMBOL(jiffies_to_msecs);
 258
 259unsigned int jiffies_to_usecs(const unsigned long j)
 260{
 261#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 262        return (USEC_PER_SEC / HZ) * j;
 263#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 264        return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
 265#else
 266# if BITS_PER_LONG == 32
 267        return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
 268# else
 269        return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
 270# endif
 271#endif
 272}
 273EXPORT_SYMBOL(jiffies_to_usecs);
 274
 275/**
 276 * timespec_trunc - Truncate timespec to a granularity
 277 * @t: Timespec
 278 * @gran: Granularity in ns.
 279 *
 280 * Truncate a timespec to a granularity. gran must be smaller than a second.
 281 * Always rounds down.
 282 *
 283 * This function should be only used for timestamps returned by
 284 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
 285 * it doesn't handle the better resolution of the latter.
 286 */
 287struct timespec timespec_trunc(struct timespec t, unsigned gran)
 288{
 289        /*
 290         * Division is pretty slow so avoid it for common cases.
 291         * Currently current_kernel_time() never returns better than
 292         * jiffies resolution. Exploit that.
 293         */
 294        if (gran <= jiffies_to_usecs(1) * 1000) {
 295                /* nothing */
 296        } else if (gran == 1000000000) {
 297                t.tv_nsec = 0;
 298        } else {
 299                t.tv_nsec -= t.tv_nsec % gran;
 300        }
 301        return t;
 302}
 303EXPORT_SYMBOL(timespec_trunc);
 304
 305/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 306 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 307 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 308 *
 309 * [For the Julian calendar (which was used in Russia before 1917,
 310 * Britain & colonies before 1752, anywhere else before 1582,
 311 * and is still in use by some communities) leave out the
 312 * -year/100+year/400 terms, and add 10.]
 313 *
 314 * This algorithm was first published by Gauss (I think).
 315 *
 316 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 317 * machines where long is 32-bit! (However, as time_t is signed, we
 318 * will already get problems at other places on 2038-01-19 03:14:08)
 319 */
 320unsigned long
 321mktime(const unsigned int year0, const unsigned int mon0,
 322       const unsigned int day, const unsigned int hour,
 323       const unsigned int min, const unsigned int sec)
 324{
 325        unsigned int mon = mon0, year = year0;
 326
 327        /* 1..12 -> 11,12,1..10 */
 328        if (0 >= (int) (mon -= 2)) {
 329                mon += 12;      /* Puts Feb last since it has leap day */
 330                year -= 1;
 331        }
 332
 333        return ((((unsigned long)
 334                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
 335                  year*365 - 719499
 336            )*24 + hour /* now have hours */
 337          )*60 + min /* now have minutes */
 338        )*60 + sec; /* finally seconds */
 339}
 340
 341EXPORT_SYMBOL(mktime);
 342
 343/**
 344 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 345 *
 346 * @ts:         pointer to timespec variable to be set
 347 * @sec:        seconds to set
 348 * @nsec:       nanoseconds to set
 349 *
 350 * Set seconds and nanoseconds field of a timespec variable and
 351 * normalize to the timespec storage format
 352 *
 353 * Note: The tv_nsec part is always in the range of
 354 *      0 <= tv_nsec < NSEC_PER_SEC
 355 * For negative values only the tv_sec field is negative !
 356 */
 357void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
 358{
 359        while (nsec >= NSEC_PER_SEC) {
 360                /*
 361                 * The following asm() prevents the compiler from
 362                 * optimising this loop into a modulo operation. See
 363                 * also __iter_div_u64_rem() in include/linux/time.h
 364                 */
 365                asm("" : "+rm"(nsec));
 366                nsec -= NSEC_PER_SEC;
 367                ++sec;
 368        }
 369        while (nsec < 0) {
 370                asm("" : "+rm"(nsec));
 371                nsec += NSEC_PER_SEC;
 372                --sec;
 373        }
 374        ts->tv_sec = sec;
 375        ts->tv_nsec = nsec;
 376}
 377EXPORT_SYMBOL(set_normalized_timespec);
 378
 379/**
 380 * ns_to_timespec - Convert nanoseconds to timespec
 381 * @nsec:       the nanoseconds value to be converted
 382 *
 383 * Returns the timespec representation of the nsec parameter.
 384 */
 385struct timespec ns_to_timespec(const s64 nsec)
 386{
 387        struct timespec ts;
 388        s32 rem;
 389
 390        if (!nsec)
 391                return (struct timespec) {0, 0};
 392
 393        ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
 394        if (unlikely(rem < 0)) {
 395                ts.tv_sec--;
 396                rem += NSEC_PER_SEC;
 397        }
 398        ts.tv_nsec = rem;
 399
 400        return ts;
 401}
 402EXPORT_SYMBOL(ns_to_timespec);
 403
 404/**
 405 * ns_to_timeval - Convert nanoseconds to timeval
 406 * @nsec:       the nanoseconds value to be converted
 407 *
 408 * Returns the timeval representation of the nsec parameter.
 409 */
 410struct timeval ns_to_timeval(const s64 nsec)
 411{
 412        struct timespec ts = ns_to_timespec(nsec);
 413        struct timeval tv;
 414
 415        tv.tv_sec = ts.tv_sec;
 416        tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
 417
 418        return tv;
 419}
 420EXPORT_SYMBOL(ns_to_timeval);
 421
 422/*
 423 * When we convert to jiffies then we interpret incoming values
 424 * the following way:
 425 *
 426 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 427 *
 428 * - 'too large' values [that would result in larger than
 429 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 430 *
 431 * - all other values are converted to jiffies by either multiplying
 432 *   the input value by a factor or dividing it with a factor
 433 *
 434 * We must also be careful about 32-bit overflows.
 435 */
 436unsigned long msecs_to_jiffies(const unsigned int m)
 437{
 438        /*
 439         * Negative value, means infinite timeout:
 440         */
 441        if ((int)m < 0)
 442                return MAX_JIFFY_OFFSET;
 443
 444#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 445        /*
 446         * HZ is equal to or smaller than 1000, and 1000 is a nice
 447         * round multiple of HZ, divide with the factor between them,
 448         * but round upwards:
 449         */
 450        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
 451#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 452        /*
 453         * HZ is larger than 1000, and HZ is a nice round multiple of
 454         * 1000 - simply multiply with the factor between them.
 455         *
 456         * But first make sure the multiplication result cannot
 457         * overflow:
 458         */
 459        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 460                return MAX_JIFFY_OFFSET;
 461
 462        return m * (HZ / MSEC_PER_SEC);
 463#else
 464        /*
 465         * Generic case - multiply, round and divide. But first
 466         * check that if we are doing a net multiplication, that
 467         * we wouldn't overflow:
 468         */
 469        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 470                return MAX_JIFFY_OFFSET;
 471
 472        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 473                >> MSEC_TO_HZ_SHR32;
 474#endif
 475}
 476EXPORT_SYMBOL(msecs_to_jiffies);
 477
 478unsigned long usecs_to_jiffies(const unsigned int u)
 479{
 480        if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
 481                return MAX_JIFFY_OFFSET;
 482#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 483        return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
 484#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 485        return u * (HZ / USEC_PER_SEC);
 486#else
 487        return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
 488                >> USEC_TO_HZ_SHR32;
 489#endif
 490}
 491EXPORT_SYMBOL(usecs_to_jiffies);
 492
 493/*
 494 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 495 * that a remainder subtract here would not do the right thing as the
 496 * resolution values don't fall on second boundries.  I.e. the line:
 497 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 498 *
 499 * Rather, we just shift the bits off the right.
 500 *
 501 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 502 * value to a scaled second value.
 503 */
 504unsigned long
 505timespec_to_jiffies(const struct timespec *value)
 506{
 507        unsigned long sec = value->tv_sec;
 508        long nsec = value->tv_nsec + TICK_NSEC - 1;
 509
 510        if (sec >= MAX_SEC_IN_JIFFIES){
 511                sec = MAX_SEC_IN_JIFFIES;
 512                nsec = 0;
 513        }
 514        return (((u64)sec * SEC_CONVERSION) +
 515                (((u64)nsec * NSEC_CONVERSION) >>
 516                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 517
 518}
 519EXPORT_SYMBOL(timespec_to_jiffies);
 520
 521void
 522jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
 523{
 524        /*
 525         * Convert jiffies to nanoseconds and separate with
 526         * one divide.
 527         */
 528        u32 rem;
 529        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 530                                    NSEC_PER_SEC, &rem);
 531        value->tv_nsec = rem;
 532}
 533EXPORT_SYMBOL(jiffies_to_timespec);
 534
 535/* Same for "timeval"
 536 *
 537 * Well, almost.  The problem here is that the real system resolution is
 538 * in nanoseconds and the value being converted is in micro seconds.
 539 * Also for some machines (those that use HZ = 1024, in-particular),
 540 * there is a LARGE error in the tick size in microseconds.
 541
 542 * The solution we use is to do the rounding AFTER we convert the
 543 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 544 * Instruction wise, this should cost only an additional add with carry
 545 * instruction above the way it was done above.
 546 */
 547unsigned long
 548timeval_to_jiffies(const struct timeval *value)
 549{
 550        unsigned long sec = value->tv_sec;
 551        long usec = value->tv_usec;
 552
 553        if (sec >= MAX_SEC_IN_JIFFIES){
 554                sec = MAX_SEC_IN_JIFFIES;
 555                usec = 0;
 556        }
 557        return (((u64)sec * SEC_CONVERSION) +
 558                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
 559                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 560}
 561EXPORT_SYMBOL(timeval_to_jiffies);
 562
 563void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
 564{
 565        /*
 566         * Convert jiffies to nanoseconds and separate with
 567         * one divide.
 568         */
 569        u32 rem;
 570
 571        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 572                                    NSEC_PER_SEC, &rem);
 573        value->tv_usec = rem / NSEC_PER_USEC;
 574}
 575EXPORT_SYMBOL(jiffies_to_timeval);
 576
 577/*
 578 * Convert jiffies/jiffies_64 to clock_t and back.
 579 */
 580clock_t jiffies_to_clock_t(unsigned long x)
 581{
 582#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 583# if HZ < USER_HZ
 584        return x * (USER_HZ / HZ);
 585# else
 586        return x / (HZ / USER_HZ);
 587# endif
 588#else
 589        return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
 590#endif
 591}
 592EXPORT_SYMBOL(jiffies_to_clock_t);
 593
 594unsigned long clock_t_to_jiffies(unsigned long x)
 595{
 596#if (HZ % USER_HZ)==0
 597        if (x >= ~0UL / (HZ / USER_HZ))
 598                return ~0UL;
 599        return x * (HZ / USER_HZ);
 600#else
 601        /* Don't worry about loss of precision here .. */
 602        if (x >= ~0UL / HZ * USER_HZ)
 603                return ~0UL;
 604
 605        /* .. but do try to contain it here */
 606        return div_u64((u64)x * HZ, USER_HZ);
 607#endif
 608}
 609EXPORT_SYMBOL(clock_t_to_jiffies);
 610
 611u64 jiffies_64_to_clock_t(u64 x)
 612{
 613#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 614# if HZ < USER_HZ
 615        x = div_u64(x * USER_HZ, HZ);
 616# elif HZ > USER_HZ
 617        x = div_u64(x, HZ / USER_HZ);
 618# else
 619        /* Nothing to do */
 620# endif
 621#else
 622        /*
 623         * There are better ways that don't overflow early,
 624         * but even this doesn't overflow in hundreds of years
 625         * in 64 bits, so..
 626         */
 627        x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 628#endif
 629        return x;
 630}
 631EXPORT_SYMBOL(jiffies_64_to_clock_t);
 632
 633u64 nsec_to_clock_t(u64 x)
 634{
 635#if (NSEC_PER_SEC % USER_HZ) == 0
 636        return div_u64(x, NSEC_PER_SEC / USER_HZ);
 637#elif (USER_HZ % 512) == 0
 638        return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
 639#else
 640        /*
 641         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
 642         * overflow after 64.99 years.
 643         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
 644         */
 645        return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
 646#endif
 647}
 648
 649/**
 650 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
 651 *
 652 * @n:  nsecs in u64
 653 *
 654 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 655 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 656 * for scheduler, not for use in device drivers to calculate timeout value.
 657 *
 658 * note:
 659 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 660 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 661 */
 662u64 nsecs_to_jiffies64(u64 n)
 663{
 664#if (NSEC_PER_SEC % HZ) == 0
 665        /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
 666        return div_u64(n, NSEC_PER_SEC / HZ);
 667#elif (HZ % 512) == 0
 668        /* overflow after 292 years if HZ = 1024 */
 669        return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
 670#else
 671        /*
 672         * Generic case - optimized for cases where HZ is a multiple of 3.
 673         * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
 674         */
 675        return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
 676#endif
 677}
 678
 679/**
 680 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
 681 *
 682 * @n:  nsecs in u64
 683 *
 684 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 685 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 686 * for scheduler, not for use in device drivers to calculate timeout value.
 687 *
 688 * note:
 689 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 690 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 691 */
 692unsigned long nsecs_to_jiffies(u64 n)
 693{
 694        return (unsigned long)nsecs_to_jiffies64(n);
 695}
 696
 697/*
 698 * Add two timespec values and do a safety check for overflow.
 699 * It's assumed that both values are valid (>= 0)
 700 */
 701struct timespec timespec_add_safe(const struct timespec lhs,
 702                                  const struct timespec rhs)
 703{
 704        struct timespec res;
 705
 706        set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
 707                                lhs.tv_nsec + rhs.tv_nsec);
 708
 709        if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
 710                res.tv_sec = TIME_T_MAX;
 711
 712        return res;
 713}
 714
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