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/core.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        if (sys_tz.tz_minuteswest != 0) {
 142                struct timespec adjust;
 143
 144                persistent_clock_is_local = 1;
 145                adjust.tv_sec = sys_tz.tz_minuteswest * 60;
 146                adjust.tv_nsec = 0;
 147                timekeeping_inject_offset(&adjust);
 148        }
 149}
 150
 151/*
 152 * In case for some reason the CMOS clock has not already been running
 153 * in UTC, but in some local time: The first time we set the timezone,
 154 * we will warp the clock so that it is ticking UTC time instead of
 155 * local time. Presumably, if someone is setting the timezone then we
 156 * are running in an environment where the programs understand about
 157 * timezones. This should be done at boot time in the /etc/rc script,
 158 * as soon as possible, so that the clock can be set right. Otherwise,
 159 * various programs will get confused when the clock gets warped.
 160 */
 161
 162int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
 163{
 164        static int firsttime = 1;
 165        int error = 0;
 166
 167        if (tv && !timespec_valid(tv))
 168                return -EINVAL;
 169
 170        error = security_settime(tv, tz);
 171        if (error)
 172                return error;
 173
 174        if (tz) {
 175                sys_tz = *tz;
 176                update_vsyscall_tz();
 177                if (firsttime) {
 178                        firsttime = 0;
 179                        if (!tv)
 180                                warp_clock();
 181                }
 182        }
 183        if (tv)
 184                return do_settimeofday(tv);
 185        return 0;
 186}
 187
 188SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
 189                struct timezone __user *, tz)
 190{
 191        struct timeval user_tv;
 192        struct timespec new_ts;
 193        struct timezone new_tz;
 194
 195        if (tv) {
 196                if (copy_from_user(&user_tv, tv, sizeof(*tv)))
 197                        return -EFAULT;
 198                new_ts.tv_sec = user_tv.tv_sec;
 199                new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
 200        }
 201        if (tz) {
 202                if (copy_from_user(&new_tz, tz, sizeof(*tz)))
 203                        return -EFAULT;
 204        }
 205
 206        return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
 207}
 208
 209SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
 210{
 211        struct timex txc;               /* Local copy of parameter */
 212        int ret;
 213
 214        /* Copy the user data space into the kernel copy
 215         * structure. But bear in mind that the structures
 216         * may change
 217         */
 218        if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
 219                return -EFAULT;
 220        ret = do_adjtimex(&txc);
 221        return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
 222}
 223
 224/**
 225 * current_fs_time - Return FS time
 226 * @sb: Superblock.
 227 *
 228 * Return the current time truncated to the time granularity supported by
 229 * the fs.
 230 */
 231struct timespec current_fs_time(struct super_block *sb)
 232{
 233        struct timespec now = current_kernel_time();
 234        return timespec_trunc(now, sb->s_time_gran);
 235}
 236EXPORT_SYMBOL(current_fs_time);
 237
 238/*
 239 * Convert jiffies to milliseconds and back.
 240 *
 241 * Avoid unnecessary multiplications/divisions in the
 242 * two most common HZ cases:
 243 */
 244unsigned int jiffies_to_msecs(const unsigned long j)
 245{
 246#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 247        return (MSEC_PER_SEC / HZ) * j;
 248#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 249        return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
 250#else
 251# if BITS_PER_LONG == 32
 252        return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
 253# else
 254        return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
 255# endif
 256#endif
 257}
 258EXPORT_SYMBOL(jiffies_to_msecs);
 259
 260unsigned int jiffies_to_usecs(const unsigned long j)
 261{
 262#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 263        return (USEC_PER_SEC / HZ) * j;
 264#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 265        return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
 266#else
 267# if BITS_PER_LONG == 32
 268        return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
 269# else
 270        return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
 271# endif
 272#endif
 273}
 274EXPORT_SYMBOL(jiffies_to_usecs);
 275
 276/**
 277 * timespec_trunc - Truncate timespec to a granularity
 278 * @t: Timespec
 279 * @gran: Granularity in ns.
 280 *
 281 * Truncate a timespec to a granularity. gran must be smaller than a second.
 282 * Always rounds down.
 283 *
 284 * This function should be only used for timestamps returned by
 285 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
 286 * it doesn't handle the better resolution of the latter.
 287 */
 288struct timespec timespec_trunc(struct timespec t, unsigned gran)
 289{
 290        /*
 291         * Division is pretty slow so avoid it for common cases.
 292         * Currently current_kernel_time() never returns better than
 293         * jiffies resolution. Exploit that.
 294         */
 295        if (gran <= jiffies_to_usecs(1) * 1000) {
 296                /* nothing */
 297        } else if (gran == 1000000000) {
 298                t.tv_nsec = 0;
 299        } else {
 300                t.tv_nsec -= t.tv_nsec % gran;
 301        }
 302        return t;
 303}
 304EXPORT_SYMBOL(timespec_trunc);
 305
 306/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 307 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 308 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 309 *
 310 * [For the Julian calendar (which was used in Russia before 1917,
 311 * Britain & colonies before 1752, anywhere else before 1582,
 312 * and is still in use by some communities) leave out the
 313 * -year/100+year/400 terms, and add 10.]
 314 *
 315 * This algorithm was first published by Gauss (I think).
 316 *
 317 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 318 * machines where long is 32-bit! (However, as time_t is signed, we
 319 * will already get problems at other places on 2038-01-19 03:14:08)
 320 */
 321unsigned long
 322mktime(const unsigned int year0, const unsigned int mon0,
 323       const unsigned int day, const unsigned int hour,
 324       const unsigned int min, const unsigned int sec)
 325{
 326        unsigned int mon = mon0, year = year0;
 327
 328        /* 1..12 -> 11,12,1..10 */
 329        if (0 >= (int) (mon -= 2)) {
 330                mon += 12;      /* Puts Feb last since it has leap day */
 331                year -= 1;
 332        }
 333
 334        return ((((unsigned long)
 335                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
 336                  year*365 - 719499
 337            )*24 + hour /* now have hours */
 338          )*60 + min /* now have minutes */
 339        )*60 + sec; /* finally seconds */
 340}
 341
 342EXPORT_SYMBOL(mktime);
 343
 344/**
 345 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 346 *
 347 * @ts:         pointer to timespec variable to be set
 348 * @sec:        seconds to set
 349 * @nsec:       nanoseconds to set
 350 *
 351 * Set seconds and nanoseconds field of a timespec variable and
 352 * normalize to the timespec storage format
 353 *
 354 * Note: The tv_nsec part is always in the range of
 355 *      0 <= tv_nsec < NSEC_PER_SEC
 356 * For negative values only the tv_sec field is negative !
 357 */
 358void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
 359{
 360        while (nsec >= NSEC_PER_SEC) {
 361                /*
 362                 * The following asm() prevents the compiler from
 363                 * optimising this loop into a modulo operation. See
 364                 * also __iter_div_u64_rem() in include/linux/time.h
 365                 */
 366                asm("" : "+rm"(nsec));
 367                nsec -= NSEC_PER_SEC;
 368                ++sec;
 369        }
 370        while (nsec < 0) {
 371                asm("" : "+rm"(nsec));
 372                nsec += NSEC_PER_SEC;
 373                --sec;
 374        }
 375        ts->tv_sec = sec;
 376        ts->tv_nsec = nsec;
 377}
 378EXPORT_SYMBOL(set_normalized_timespec);
 379
 380/**
 381 * ns_to_timespec - Convert nanoseconds to timespec
 382 * @nsec:       the nanoseconds value to be converted
 383 *
 384 * Returns the timespec representation of the nsec parameter.
 385 */
 386struct timespec ns_to_timespec(const s64 nsec)
 387{
 388        struct timespec ts;
 389        s32 rem;
 390
 391        if (!nsec)
 392                return (struct timespec) {0, 0};
 393
 394        ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
 395        if (unlikely(rem < 0)) {
 396                ts.tv_sec--;
 397                rem += NSEC_PER_SEC;
 398        }
 399        ts.tv_nsec = rem;
 400
 401        return ts;
 402}
 403EXPORT_SYMBOL(ns_to_timespec);
 404
 405/**
 406 * ns_to_timeval - Convert nanoseconds to timeval
 407 * @nsec:       the nanoseconds value to be converted
 408 *
 409 * Returns the timeval representation of the nsec parameter.
 410 */
 411struct timeval ns_to_timeval(const s64 nsec)
 412{
 413        struct timespec ts = ns_to_timespec(nsec);
 414        struct timeval tv;
 415
 416        tv.tv_sec = ts.tv_sec;
 417        tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
 418
 419        return tv;
 420}
 421EXPORT_SYMBOL(ns_to_timeval);
 422
 423/*
 424 * When we convert to jiffies then we interpret incoming values
 425 * the following way:
 426 *
 427 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 428 *
 429 * - 'too large' values [that would result in larger than
 430 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 431 *
 432 * - all other values are converted to jiffies by either multiplying
 433 *   the input value by a factor or dividing it with a factor
 434 *
 435 * We must also be careful about 32-bit overflows.
 436 */
 437unsigned long msecs_to_jiffies(const unsigned int m)
 438{
 439        /*
 440         * Negative value, means infinite timeout:
 441         */
 442        if ((int)m < 0)
 443                return MAX_JIFFY_OFFSET;
 444
 445#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 446        /*
 447         * HZ is equal to or smaller than 1000, and 1000 is a nice
 448         * round multiple of HZ, divide with the factor between them,
 449         * but round upwards:
 450         */
 451        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
 452#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 453        /*
 454         * HZ is larger than 1000, and HZ is a nice round multiple of
 455         * 1000 - simply multiply with the factor between them.
 456         *
 457         * But first make sure the multiplication result cannot
 458         * overflow:
 459         */
 460        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 461                return MAX_JIFFY_OFFSET;
 462
 463        return m * (HZ / MSEC_PER_SEC);
 464#else
 465        /*
 466         * Generic case - multiply, round and divide. But first
 467         * check that if we are doing a net multiplication, that
 468         * we wouldn't overflow:
 469         */
 470        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 471                return MAX_JIFFY_OFFSET;
 472
 473        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 474                >> MSEC_TO_HZ_SHR32;
 475#endif
 476}
 477EXPORT_SYMBOL(msecs_to_jiffies);
 478
 479unsigned long usecs_to_jiffies(const unsigned int u)
 480{
 481        if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
 482                return MAX_JIFFY_OFFSET;
 483#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 484        return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
 485#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 486        return u * (HZ / USEC_PER_SEC);
 487#else
 488        return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
 489                >> USEC_TO_HZ_SHR32;
 490#endif
 491}
 492EXPORT_SYMBOL(usecs_to_jiffies);
 493
 494/*
 495 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 496 * that a remainder subtract here would not do the right thing as the
 497 * resolution values don't fall on second boundries.  I.e. the line:
 498 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 499 *
 500 * Rather, we just shift the bits off the right.
 501 *
 502 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 503 * value to a scaled second value.
 504 */
 505unsigned long
 506timespec_to_jiffies(const struct timespec *value)
 507{
 508        unsigned long sec = value->tv_sec;
 509        long nsec = value->tv_nsec + TICK_NSEC - 1;
 510
 511        if (sec >= MAX_SEC_IN_JIFFIES){
 512                sec = MAX_SEC_IN_JIFFIES;
 513                nsec = 0;
 514        }
 515        return (((u64)sec * SEC_CONVERSION) +
 516                (((u64)nsec * NSEC_CONVERSION) >>
 517                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 518
 519}
 520EXPORT_SYMBOL(timespec_to_jiffies);
 521
 522void
 523jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
 524{
 525        /*
 526         * Convert jiffies to nanoseconds and separate with
 527         * one divide.
 528         */
 529        u32 rem;
 530        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 531                                    NSEC_PER_SEC, &rem);
 532        value->tv_nsec = rem;
 533}
 534EXPORT_SYMBOL(jiffies_to_timespec);
 535
 536/* Same for "timeval"
 537 *
 538 * Well, almost.  The problem here is that the real system resolution is
 539 * in nanoseconds and the value being converted is in micro seconds.
 540 * Also for some machines (those that use HZ = 1024, in-particular),
 541 * there is a LARGE error in the tick size in microseconds.
 542
 543 * The solution we use is to do the rounding AFTER we convert the
 544 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 545 * Instruction wise, this should cost only an additional add with carry
 546 * instruction above the way it was done above.
 547 */
 548unsigned long
 549timeval_to_jiffies(const struct timeval *value)
 550{
 551        unsigned long sec = value->tv_sec;
 552        long usec = value->tv_usec;
 553
 554        if (sec >= MAX_SEC_IN_JIFFIES){
 555                sec = MAX_SEC_IN_JIFFIES;
 556                usec = 0;
 557        }
 558        return (((u64)sec * SEC_CONVERSION) +
 559                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
 560                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 561}
 562EXPORT_SYMBOL(timeval_to_jiffies);
 563
 564void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
 565{
 566        /*
 567         * Convert jiffies to nanoseconds and separate with
 568         * one divide.
 569         */
 570        u32 rem;
 571
 572        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 573                                    NSEC_PER_SEC, &rem);
 574        value->tv_usec = rem / NSEC_PER_USEC;
 575}
 576EXPORT_SYMBOL(jiffies_to_timeval);
 577
 578/*
 579 * Convert jiffies/jiffies_64 to clock_t and back.
 580 */
 581clock_t jiffies_to_clock_t(unsigned long x)
 582{
 583#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 584# if HZ < USER_HZ
 585        return x * (USER_HZ / HZ);
 586# else
 587        return x / (HZ / USER_HZ);
 588# endif
 589#else
 590        return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
 591#endif
 592}
 593EXPORT_SYMBOL(jiffies_to_clock_t);
 594
 595unsigned long clock_t_to_jiffies(unsigned long x)
 596{
 597#if (HZ % USER_HZ)==0
 598        if (x >= ~0UL / (HZ / USER_HZ))
 599                return ~0UL;
 600        return x * (HZ / USER_HZ);
 601#else
 602        /* Don't worry about loss of precision here .. */
 603        if (x >= ~0UL / HZ * USER_HZ)
 604                return ~0UL;
 605
 606        /* .. but do try to contain it here */
 607        return div_u64((u64)x * HZ, USER_HZ);
 608#endif
 609}
 610EXPORT_SYMBOL(clock_t_to_jiffies);
 611
 612u64 jiffies_64_to_clock_t(u64 x)
 613{
 614#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 615# if HZ < USER_HZ
 616        x = div_u64(x * USER_HZ, HZ);
 617# elif HZ > USER_HZ
 618        x = div_u64(x, HZ / USER_HZ);
 619# else
 620        /* Nothing to do */
 621# endif
 622#else
 623        /*
 624         * There are better ways that don't overflow early,
 625         * but even this doesn't overflow in hundreds of years
 626         * in 64 bits, so..
 627         */
 628        x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 629#endif
 630        return x;
 631}
 632EXPORT_SYMBOL(jiffies_64_to_clock_t);
 633
 634u64 nsec_to_clock_t(u64 x)
 635{
 636#if (NSEC_PER_SEC % USER_HZ) == 0
 637        return div_u64(x, NSEC_PER_SEC / USER_HZ);
 638#elif (USER_HZ % 512) == 0
 639        return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
 640#else
 641        /*
 642         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
 643         * overflow after 64.99 years.
 644         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
 645         */
 646        return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
 647#endif
 648}
 649
 650/**
 651 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
 652 *
 653 * @n:  nsecs in u64
 654 *
 655 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 656 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 657 * for scheduler, not for use in device drivers to calculate timeout value.
 658 *
 659 * note:
 660 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 661 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 662 */
 663u64 nsecs_to_jiffies64(u64 n)
 664{
 665#if (NSEC_PER_SEC % HZ) == 0
 666        /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
 667        return div_u64(n, NSEC_PER_SEC / HZ);
 668#elif (HZ % 512) == 0
 669        /* overflow after 292 years if HZ = 1024 */
 670        return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
 671#else
 672        /*
 673         * Generic case - optimized for cases where HZ is a multiple of 3.
 674         * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
 675         */
 676        return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
 677#endif
 678}
 679
 680/**
 681 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
 682 *
 683 * @n:  nsecs in u64
 684 *
 685 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 686 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 687 * for scheduler, not for use in device drivers to calculate timeout value.
 688 *
 689 * note:
 690 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 691 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 692 */
 693unsigned long nsecs_to_jiffies(u64 n)
 694{
 695        return (unsigned long)nsecs_to_jiffies64(n);
 696}
 697
 698/*
 699 * Add two timespec values and do a safety check for overflow.
 700 * It's assumed that both values are valid (>= 0)
 701 */
 702struct timespec timespec_add_safe(const struct timespec lhs,
 703                                  const struct timespec rhs)
 704{
 705        struct timespec res;
 706
 707        set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
 708                                lhs.tv_nsec + rhs.tv_nsec);
 709
 710        if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
 711                res.tv_sec = TIME_T_MAX;
 712
 713        return res;
 714}
 715
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