linux/kernel/time.c
<<
>>
Prefs
   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/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 * Adjust the time obtained from the CMOS to be UTC time instead of
 119 * local time.
 120 *
 121 * This is ugly, but preferable to the alternatives.  Otherwise we
 122 * would either need to write a program to do it in /etc/rc (and risk
 123 * confusion if the program gets run more than once; it would also be
 124 * hard to make the program warp the clock precisely n hours)  or
 125 * compile in the timezone information into the kernel.  Bad, bad....
 126 *
 127 *                                              - TYT, 1992-01-01
 128 *
 129 * The best thing to do is to keep the CMOS clock in universal time (UTC)
 130 * as real UNIX machines always do it. This avoids all headaches about
 131 * daylight saving times and warping kernel clocks.
 132 */
 133static inline void warp_clock(void)
 134{
 135        struct timespec adjust;
 136
 137        adjust = current_kernel_time();
 138        adjust.tv_sec += sys_tz.tz_minuteswest * 60;
 139        do_settimeofday(&adjust);
 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(const struct timespec *tv, const 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
 185SYSCALL_DEFINE2(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
 206SYSCALL_DEFINE1(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 */
 241inline unsigned int 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
 257inline unsigned int 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/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 304 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 305 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 306 *
 307 * [For the Julian calendar (which was used in Russia before 1917,
 308 * Britain & colonies before 1752, anywhere else before 1582,
 309 * and is still in use by some communities) leave out the
 310 * -year/100+year/400 terms, and add 10.]
 311 *
 312 * This algorithm was first published by Gauss (I think).
 313 *
 314 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 315 * machines where long is 32-bit! (However, as time_t is signed, we
 316 * will already get problems at other places on 2038-01-19 03:14:08)
 317 */
 318unsigned long
 319mktime(const unsigned int year0, const unsigned int mon0,
 320       const unsigned int day, const unsigned int hour,
 321       const unsigned int min, const unsigned int sec)
 322{
 323        unsigned int mon = mon0, year = year0;
 324
 325        /* 1..12 -> 11,12,1..10 */
 326        if (0 >= (int) (mon -= 2)) {
 327                mon += 12;      /* Puts Feb last since it has leap day */
 328                year -= 1;
 329        }
 330
 331        return ((((unsigned long)
 332                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
 333                  year*365 - 719499
 334            )*24 + hour /* now have hours */
 335          )*60 + min /* now have minutes */
 336        )*60 + sec; /* finally seconds */
 337}
 338
 339EXPORT_SYMBOL(mktime);
 340
 341/**
 342 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 343 *
 344 * @ts:         pointer to timespec variable to be set
 345 * @sec:        seconds to set
 346 * @nsec:       nanoseconds to set
 347 *
 348 * Set seconds and nanoseconds field of a timespec variable and
 349 * normalize to the timespec storage format
 350 *
 351 * Note: The tv_nsec part is always in the range of
 352 *      0 <= tv_nsec < NSEC_PER_SEC
 353 * For negative values only the tv_sec field is negative !
 354 */
 355void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
 356{
 357        while (nsec >= NSEC_PER_SEC) {
 358                /*
 359                 * The following asm() prevents the compiler from
 360                 * optimising this loop into a modulo operation. See
 361                 * also __iter_div_u64_rem() in include/linux/time.h
 362                 */
 363                asm("" : "+rm"(nsec));
 364                nsec -= NSEC_PER_SEC;
 365                ++sec;
 366        }
 367        while (nsec < 0) {
 368                asm("" : "+rm"(nsec));
 369                nsec += NSEC_PER_SEC;
 370                --sec;
 371        }
 372        ts->tv_sec = sec;
 373        ts->tv_nsec = nsec;
 374}
 375EXPORT_SYMBOL(set_normalized_timespec);
 376
 377/**
 378 * ns_to_timespec - Convert nanoseconds to timespec
 379 * @nsec:       the nanoseconds value to be converted
 380 *
 381 * Returns the timespec representation of the nsec parameter.
 382 */
 383struct timespec ns_to_timespec(const s64 nsec)
 384{
 385        struct timespec ts;
 386        s32 rem;
 387
 388        if (!nsec)
 389                return (struct timespec) {0, 0};
 390
 391        ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
 392        if (unlikely(rem < 0)) {
 393                ts.tv_sec--;
 394                rem += NSEC_PER_SEC;
 395        }
 396        ts.tv_nsec = rem;
 397
 398        return ts;
 399}
 400EXPORT_SYMBOL(ns_to_timespec);
 401
 402/**
 403 * ns_to_timeval - Convert nanoseconds to timeval
 404 * @nsec:       the nanoseconds value to be converted
 405 *
 406 * Returns the timeval representation of the nsec parameter.
 407 */
 408struct timeval ns_to_timeval(const s64 nsec)
 409{
 410        struct timespec ts = ns_to_timespec(nsec);
 411        struct timeval tv;
 412
 413        tv.tv_sec = ts.tv_sec;
 414        tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
 415
 416        return tv;
 417}
 418EXPORT_SYMBOL(ns_to_timeval);
 419
 420/*
 421 * When we convert to jiffies then we interpret incoming values
 422 * the following way:
 423 *
 424 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 425 *
 426 * - 'too large' values [that would result in larger than
 427 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 428 *
 429 * - all other values are converted to jiffies by either multiplying
 430 *   the input value by a factor or dividing it with a factor
 431 *
 432 * We must also be careful about 32-bit overflows.
 433 */
 434unsigned long msecs_to_jiffies(const unsigned int m)
 435{
 436        /*
 437         * Negative value, means infinite timeout:
 438         */
 439        if ((int)m < 0)
 440                return MAX_JIFFY_OFFSET;
 441
 442#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 443        /*
 444         * HZ is equal to or smaller than 1000, and 1000 is a nice
 445         * round multiple of HZ, divide with the factor between them,
 446         * but round upwards:
 447         */
 448        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
 449#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 450        /*
 451         * HZ is larger than 1000, and HZ is a nice round multiple of
 452         * 1000 - simply multiply with the factor between them.
 453         *
 454         * But first make sure the multiplication result cannot
 455         * overflow:
 456         */
 457        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 458                return MAX_JIFFY_OFFSET;
 459
 460        return m * (HZ / MSEC_PER_SEC);
 461#else
 462        /*
 463         * Generic case - multiply, round and divide. But first
 464         * check that if we are doing a net multiplication, that
 465         * we wouldn't overflow:
 466         */
 467        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 468                return MAX_JIFFY_OFFSET;
 469
 470        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 471                >> MSEC_TO_HZ_SHR32;
 472#endif
 473}
 474EXPORT_SYMBOL(msecs_to_jiffies);
 475
 476unsigned long usecs_to_jiffies(const unsigned int u)
 477{
 478        if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
 479                return MAX_JIFFY_OFFSET;
 480#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 481        return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
 482#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 483        return u * (HZ / USEC_PER_SEC);
 484#else
 485        return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
 486                >> USEC_TO_HZ_SHR32;
 487#endif
 488}
 489EXPORT_SYMBOL(usecs_to_jiffies);
 490
 491/*
 492 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 493 * that a remainder subtract here would not do the right thing as the
 494 * resolution values don't fall on second boundries.  I.e. the line:
 495 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 496 *
 497 * Rather, we just shift the bits off the right.
 498 *
 499 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 500 * value to a scaled second value.
 501 */
 502unsigned long
 503timespec_to_jiffies(const struct timespec *value)
 504{
 505        unsigned long sec = value->tv_sec;
 506        long nsec = value->tv_nsec + TICK_NSEC - 1;
 507
 508        if (sec >= MAX_SEC_IN_JIFFIES){
 509                sec = MAX_SEC_IN_JIFFIES;
 510                nsec = 0;
 511        }
 512        return (((u64)sec * SEC_CONVERSION) +
 513                (((u64)nsec * NSEC_CONVERSION) >>
 514                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 515
 516}
 517EXPORT_SYMBOL(timespec_to_jiffies);
 518
 519void
 520jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
 521{
 522        /*
 523         * Convert jiffies to nanoseconds and separate with
 524         * one divide.
 525         */
 526        u32 rem;
 527        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 528                                    NSEC_PER_SEC, &rem);
 529        value->tv_nsec = rem;
 530}
 531EXPORT_SYMBOL(jiffies_to_timespec);
 532
 533/* Same for "timeval"
 534 *
 535 * Well, almost.  The problem here is that the real system resolution is
 536 * in nanoseconds and the value being converted is in micro seconds.
 537 * Also for some machines (those that use HZ = 1024, in-particular),
 538 * there is a LARGE error in the tick size in microseconds.
 539
 540 * The solution we use is to do the rounding AFTER we convert the
 541 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 542 * Instruction wise, this should cost only an additional add with carry
 543 * instruction above the way it was done above.
 544 */
 545unsigned long
 546timeval_to_jiffies(const struct timeval *value)
 547{
 548        unsigned long sec = value->tv_sec;
 549        long usec = value->tv_usec;
 550
 551        if (sec >= MAX_SEC_IN_JIFFIES){
 552                sec = MAX_SEC_IN_JIFFIES;
 553                usec = 0;
 554        }
 555        return (((u64)sec * SEC_CONVERSION) +
 556                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
 557                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 558}
 559EXPORT_SYMBOL(timeval_to_jiffies);
 560
 561void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
 562{
 563        /*
 564         * Convert jiffies to nanoseconds and separate with
 565         * one divide.
 566         */
 567        u32 rem;
 568
 569        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 570                                    NSEC_PER_SEC, &rem);
 571        value->tv_usec = rem / NSEC_PER_USEC;
 572}
 573EXPORT_SYMBOL(jiffies_to_timeval);
 574
 575/*
 576 * Convert jiffies/jiffies_64 to clock_t and back.
 577 */
 578clock_t jiffies_to_clock_t(unsigned long x)
 579{
 580#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 581# if HZ < USER_HZ
 582        return x * (USER_HZ / HZ);
 583# else
 584        return x / (HZ / USER_HZ);
 585# endif
 586#else
 587        return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
 588#endif
 589}
 590EXPORT_SYMBOL(jiffies_to_clock_t);
 591
 592unsigned long clock_t_to_jiffies(unsigned long x)
 593{
 594#if (HZ % USER_HZ)==0
 595        if (x >= ~0UL / (HZ / USER_HZ))
 596                return ~0UL;
 597        return x * (HZ / USER_HZ);
 598#else
 599        /* Don't worry about loss of precision here .. */
 600        if (x >= ~0UL / HZ * USER_HZ)
 601                return ~0UL;
 602
 603        /* .. but do try to contain it here */
 604        return div_u64((u64)x * HZ, USER_HZ);
 605#endif
 606}
 607EXPORT_SYMBOL(clock_t_to_jiffies);
 608
 609u64 jiffies_64_to_clock_t(u64 x)
 610{
 611#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 612# if HZ < USER_HZ
 613        x = div_u64(x * USER_HZ, HZ);
 614# elif HZ > USER_HZ
 615        x = div_u64(x, HZ / USER_HZ);
 616# else
 617        /* Nothing to do */
 618# endif
 619#else
 620        /*
 621         * There are better ways that don't overflow early,
 622         * but even this doesn't overflow in hundreds of years
 623         * in 64 bits, so..
 624         */
 625        x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 626#endif
 627        return x;
 628}
 629EXPORT_SYMBOL(jiffies_64_to_clock_t);
 630
 631u64 nsec_to_clock_t(u64 x)
 632{
 633#if (NSEC_PER_SEC % USER_HZ) == 0
 634        return div_u64(x, NSEC_PER_SEC / USER_HZ);
 635#elif (USER_HZ % 512) == 0
 636        return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
 637#else
 638        /*
 639         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
 640         * overflow after 64.99 years.
 641         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
 642         */
 643        return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
 644#endif
 645}
 646
 647/**
 648 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
 649 *
 650 * @n:  nsecs in u64
 651 *
 652 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 653 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 654 * for scheduler, not for use in device drivers to calculate timeout value.
 655 *
 656 * note:
 657 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 658 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 659 */
 660u64 nsecs_to_jiffies64(u64 n)
 661{
 662#if (NSEC_PER_SEC % HZ) == 0
 663        /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
 664        return div_u64(n, NSEC_PER_SEC / HZ);
 665#elif (HZ % 512) == 0
 666        /* overflow after 292 years if HZ = 1024 */
 667        return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
 668#else
 669        /*
 670         * Generic case - optimized for cases where HZ is a multiple of 3.
 671         * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
 672         */
 673        return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
 674#endif
 675}
 676
 677/**
 678 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
 679 *
 680 * @n:  nsecs in u64
 681 *
 682 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 683 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 684 * for scheduler, not for use in device drivers to calculate timeout value.
 685 *
 686 * note:
 687 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 688 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 689 */
 690unsigned long nsecs_to_jiffies(u64 n)
 691{
 692        return (unsigned long)nsecs_to_jiffies64(n);
 693}
 694
 695/*
 696 * Add two timespec values and do a safety check for overflow.
 697 * It's assumed that both values are valid (>= 0)
 698 */
 699struct timespec timespec_add_safe(const struct timespec lhs,
 700                                  const struct timespec rhs)
 701{
 702        struct timespec res;
 703
 704        set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
 705                                lhs.tv_nsec + rhs.tv_nsec);
 706
 707        if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
 708                res.tv_sec = TIME_T_MAX;
 709
 710        return res;
 711}
 712
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.