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/export.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                sys_tz = *tz;
 167                update_vsyscall_tz();
 168                if (firsttime) {
 169                        firsttime = 0;
 170                        if (!tv)
 171                                warp_clock();
 172                }
 173        }
 174        if (tv)
 175                return do_settimeofday(tv);
 176        return 0;
 177}
 178
 179SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
 180                struct timezone __user *, tz)
 181{
 182        struct timeval user_tv;
 183        struct timespec new_ts;
 184        struct timezone new_tz;
 185
 186        if (tv) {
 187                if (copy_from_user(&user_tv, tv, sizeof(*tv)))
 188                        return -EFAULT;
 189                new_ts.tv_sec = user_tv.tv_sec;
 190                new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
 191        }
 192        if (tz) {
 193                if (copy_from_user(&new_tz, tz, sizeof(*tz)))
 194                        return -EFAULT;
 195        }
 196
 197        return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
 198}
 199
 200SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
 201{
 202        struct timex txc;               /* Local copy of parameter */
 203        int ret;
 204
 205        /* Copy the user data space into the kernel copy
 206         * structure. But bear in mind that the structures
 207         * may change
 208         */
 209        if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
 210                return -EFAULT;
 211        ret = do_adjtimex(&txc);
 212        return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
 213}
 214
 215/**
 216 * current_fs_time - Return FS time
 217 * @sb: Superblock.
 218 *
 219 * Return the current time truncated to the time granularity supported by
 220 * the fs.
 221 */
 222struct timespec current_fs_time(struct super_block *sb)
 223{
 224        struct timespec now = current_kernel_time();
 225        return timespec_trunc(now, sb->s_time_gran);
 226}
 227EXPORT_SYMBOL(current_fs_time);
 228
 229/*
 230 * Convert jiffies to milliseconds and back.
 231 *
 232 * Avoid unnecessary multiplications/divisions in the
 233 * two most common HZ cases:
 234 */
 235inline unsigned int jiffies_to_msecs(const unsigned long j)
 236{
 237#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 238        return (MSEC_PER_SEC / HZ) * j;
 239#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 240        return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
 241#else
 242# if BITS_PER_LONG == 32
 243        return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
 244# else
 245        return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
 246# endif
 247#endif
 248}
 249EXPORT_SYMBOL(jiffies_to_msecs);
 250
 251inline unsigned int jiffies_to_usecs(const unsigned long j)
 252{
 253#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 254        return (USEC_PER_SEC / HZ) * j;
 255#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 256        return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
 257#else
 258# if BITS_PER_LONG == 32
 259        return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
 260# else
 261        return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
 262# endif
 263#endif
 264}
 265EXPORT_SYMBOL(jiffies_to_usecs);
 266
 267/**
 268 * timespec_trunc - Truncate timespec to a granularity
 269 * @t: Timespec
 270 * @gran: Granularity in ns.
 271 *
 272 * Truncate a timespec to a granularity. gran must be smaller than a second.
 273 * Always rounds down.
 274 *
 275 * This function should be only used for timestamps returned by
 276 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
 277 * it doesn't handle the better resolution of the latter.
 278 */
 279struct timespec timespec_trunc(struct timespec t, unsigned gran)
 280{
 281        /*
 282         * Division is pretty slow so avoid it for common cases.
 283         * Currently current_kernel_time() never returns better than
 284         * jiffies resolution. Exploit that.
 285         */
 286        if (gran <= jiffies_to_usecs(1) * 1000) {
 287                /* nothing */
 288        } else if (gran == 1000000000) {
 289                t.tv_nsec = 0;
 290        } else {
 291                t.tv_nsec -= t.tv_nsec % gran;
 292        }
 293        return t;
 294}
 295EXPORT_SYMBOL(timespec_trunc);
 296
 297/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 298 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 299 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 300 *
 301 * [For the Julian calendar (which was used in Russia before 1917,
 302 * Britain & colonies before 1752, anywhere else before 1582,
 303 * and is still in use by some communities) leave out the
 304 * -year/100+year/400 terms, and add 10.]
 305 *
 306 * This algorithm was first published by Gauss (I think).
 307 *
 308 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 309 * machines where long is 32-bit! (However, as time_t is signed, we
 310 * will already get problems at other places on 2038-01-19 03:14:08)
 311 */
 312unsigned long
 313mktime(const unsigned int year0, const unsigned int mon0,
 314       const unsigned int day, const unsigned int hour,
 315       const unsigned int min, const unsigned int sec)
 316{
 317        unsigned int mon = mon0, year = year0;
 318
 319        /* 1..12 -> 11,12,1..10 */
 320        if (0 >= (int) (mon -= 2)) {
 321                mon += 12;      /* Puts Feb last since it has leap day */
 322                year -= 1;
 323        }
 324
 325        return ((((unsigned long)
 326                  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
 327                  year*365 - 719499
 328            )*24 + hour /* now have hours */
 329          )*60 + min /* now have minutes */
 330        )*60 + sec; /* finally seconds */
 331}
 332
 333EXPORT_SYMBOL(mktime);
 334
 335/**
 336 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 337 *
 338 * @ts:         pointer to timespec variable to be set
 339 * @sec:        seconds to set
 340 * @nsec:       nanoseconds to set
 341 *
 342 * Set seconds and nanoseconds field of a timespec variable and
 343 * normalize to the timespec storage format
 344 *
 345 * Note: The tv_nsec part is always in the range of
 346 *      0 <= tv_nsec < NSEC_PER_SEC
 347 * For negative values only the tv_sec field is negative !
 348 */
 349void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
 350{
 351        while (nsec >= NSEC_PER_SEC) {
 352                /*
 353                 * The following asm() prevents the compiler from
 354                 * optimising this loop into a modulo operation. See
 355                 * also __iter_div_u64_rem() in include/linux/time.h
 356                 */
 357                asm("" : "+rm"(nsec));
 358                nsec -= NSEC_PER_SEC;
 359                ++sec;
 360        }
 361        while (nsec < 0) {
 362                asm("" : "+rm"(nsec));
 363                nsec += NSEC_PER_SEC;
 364                --sec;
 365        }
 366        ts->tv_sec = sec;
 367        ts->tv_nsec = nsec;
 368}
 369EXPORT_SYMBOL(set_normalized_timespec);
 370
 371/**
 372 * ns_to_timespec - Convert nanoseconds to timespec
 373 * @nsec:       the nanoseconds value to be converted
 374 *
 375 * Returns the timespec representation of the nsec parameter.
 376 */
 377struct timespec ns_to_timespec(const s64 nsec)
 378{
 379        struct timespec ts;
 380        s32 rem;
 381
 382        if (!nsec)
 383                return (struct timespec) {0, 0};
 384
 385        ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
 386        if (unlikely(rem < 0)) {
 387                ts.tv_sec--;
 388                rem += NSEC_PER_SEC;
 389        }
 390        ts.tv_nsec = rem;
 391
 392        return ts;
 393}
 394EXPORT_SYMBOL(ns_to_timespec);
 395
 396/**
 397 * ns_to_timeval - Convert nanoseconds to timeval
 398 * @nsec:       the nanoseconds value to be converted
 399 *
 400 * Returns the timeval representation of the nsec parameter.
 401 */
 402struct timeval ns_to_timeval(const s64 nsec)
 403{
 404        struct timespec ts = ns_to_timespec(nsec);
 405        struct timeval tv;
 406
 407        tv.tv_sec = ts.tv_sec;
 408        tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
 409
 410        return tv;
 411}
 412EXPORT_SYMBOL(ns_to_timeval);
 413
 414/*
 415 * When we convert to jiffies then we interpret incoming values
 416 * the following way:
 417 *
 418 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 419 *
 420 * - 'too large' values [that would result in larger than
 421 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 422 *
 423 * - all other values are converted to jiffies by either multiplying
 424 *   the input value by a factor or dividing it with a factor
 425 *
 426 * We must also be careful about 32-bit overflows.
 427 */
 428unsigned long msecs_to_jiffies(const unsigned int m)
 429{
 430        /*
 431         * Negative value, means infinite timeout:
 432         */
 433        if ((int)m < 0)
 434                return MAX_JIFFY_OFFSET;
 435
 436#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
 437        /*
 438         * HZ is equal to or smaller than 1000, and 1000 is a nice
 439         * round multiple of HZ, divide with the factor between them,
 440         * but round upwards:
 441         */
 442        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
 443#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 444        /*
 445         * HZ is larger than 1000, and HZ is a nice round multiple of
 446         * 1000 - simply multiply with the factor between them.
 447         *
 448         * But first make sure the multiplication result cannot
 449         * overflow:
 450         */
 451        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 452                return MAX_JIFFY_OFFSET;
 453
 454        return m * (HZ / MSEC_PER_SEC);
 455#else
 456        /*
 457         * Generic case - multiply, round and divide. But first
 458         * check that if we are doing a net multiplication, that
 459         * we wouldn't overflow:
 460         */
 461        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 462                return MAX_JIFFY_OFFSET;
 463
 464        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 465                >> MSEC_TO_HZ_SHR32;
 466#endif
 467}
 468EXPORT_SYMBOL(msecs_to_jiffies);
 469
 470unsigned long usecs_to_jiffies(const unsigned int u)
 471{
 472        if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
 473                return MAX_JIFFY_OFFSET;
 474#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
 475        return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
 476#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
 477        return u * (HZ / USEC_PER_SEC);
 478#else
 479        return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
 480                >> USEC_TO_HZ_SHR32;
 481#endif
 482}
 483EXPORT_SYMBOL(usecs_to_jiffies);
 484
 485/*
 486 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 487 * that a remainder subtract here would not do the right thing as the
 488 * resolution values don't fall on second boundries.  I.e. the line:
 489 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 490 *
 491 * Rather, we just shift the bits off the right.
 492 *
 493 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 494 * value to a scaled second value.
 495 */
 496unsigned long
 497timespec_to_jiffies(const struct timespec *value)
 498{
 499        unsigned long sec = value->tv_sec;
 500        long nsec = value->tv_nsec + TICK_NSEC - 1;
 501
 502        if (sec >= MAX_SEC_IN_JIFFIES){
 503                sec = MAX_SEC_IN_JIFFIES;
 504                nsec = 0;
 505        }
 506        return (((u64)sec * SEC_CONVERSION) +
 507                (((u64)nsec * NSEC_CONVERSION) >>
 508                 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 509
 510}
 511EXPORT_SYMBOL(timespec_to_jiffies);
 512
 513void
 514jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
 515{
 516        /*
 517         * Convert jiffies to nanoseconds and separate with
 518         * one divide.
 519         */
 520        u32 rem;
 521        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 522                                    NSEC_PER_SEC, &rem);
 523        value->tv_nsec = rem;
 524}
 525EXPORT_SYMBOL(jiffies_to_timespec);
 526
 527/* Same for "timeval"
 528 *
 529 * Well, almost.  The problem here is that the real system resolution is
 530 * in nanoseconds and the value being converted is in micro seconds.
 531 * Also for some machines (those that use HZ = 1024, in-particular),
 532 * there is a LARGE error in the tick size in microseconds.
 533
 534 * The solution we use is to do the rounding AFTER we convert the
 535 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 536 * Instruction wise, this should cost only an additional add with carry
 537 * instruction above the way it was done above.
 538 */
 539unsigned long
 540timeval_to_jiffies(const struct timeval *value)
 541{
 542        unsigned long sec = value->tv_sec;
 543        long usec = value->tv_usec;
 544
 545        if (sec >= MAX_SEC_IN_JIFFIES){
 546                sec = MAX_SEC_IN_JIFFIES;
 547                usec = 0;
 548        }
 549        return (((u64)sec * SEC_CONVERSION) +
 550                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
 551                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
 552}
 553EXPORT_SYMBOL(timeval_to_jiffies);
 554
 555void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
 556{
 557        /*
 558         * Convert jiffies to nanoseconds and separate with
 559         * one divide.
 560         */
 561        u32 rem;
 562
 563        value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
 564                                    NSEC_PER_SEC, &rem);
 565        value->tv_usec = rem / NSEC_PER_USEC;
 566}
 567EXPORT_SYMBOL(jiffies_to_timeval);
 568
 569/*
 570 * Convert jiffies/jiffies_64 to clock_t and back.
 571 */
 572clock_t jiffies_to_clock_t(unsigned long x)
 573{
 574#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 575# if HZ < USER_HZ
 576        return x * (USER_HZ / HZ);
 577# else
 578        return x / (HZ / USER_HZ);
 579# endif
 580#else
 581        return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
 582#endif
 583}
 584EXPORT_SYMBOL(jiffies_to_clock_t);
 585
 586unsigned long clock_t_to_jiffies(unsigned long x)
 587{
 588#if (HZ % USER_HZ)==0
 589        if (x >= ~0UL / (HZ / USER_HZ))
 590                return ~0UL;
 591        return x * (HZ / USER_HZ);
 592#else
 593        /* Don't worry about loss of precision here .. */
 594        if (x >= ~0UL / HZ * USER_HZ)
 595                return ~0UL;
 596
 597        /* .. but do try to contain it here */
 598        return div_u64((u64)x * HZ, USER_HZ);
 599#endif
 600}
 601EXPORT_SYMBOL(clock_t_to_jiffies);
 602
 603u64 jiffies_64_to_clock_t(u64 x)
 604{
 605#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 606# if HZ < USER_HZ
 607        x = div_u64(x * USER_HZ, HZ);
 608# elif HZ > USER_HZ
 609        x = div_u64(x, HZ / USER_HZ);
 610# else
 611        /* Nothing to do */
 612# endif
 613#else
 614        /*
 615         * There are better ways that don't overflow early,
 616         * but even this doesn't overflow in hundreds of years
 617         * in 64 bits, so..
 618         */
 619        x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 620#endif
 621        return x;
 622}
 623EXPORT_SYMBOL(jiffies_64_to_clock_t);
 624
 625u64 nsec_to_clock_t(u64 x)
 626{
 627#if (NSEC_PER_SEC % USER_HZ) == 0
 628        return div_u64(x, NSEC_PER_SEC / USER_HZ);
 629#elif (USER_HZ % 512) == 0
 630        return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
 631#else
 632        /*
 633         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
 634         * overflow after 64.99 years.
 635         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
 636         */
 637        return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
 638#endif
 639}
 640
 641/**
 642 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
 643 *
 644 * @n:  nsecs in u64
 645 *
 646 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 647 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 648 * for scheduler, not for use in device drivers to calculate timeout value.
 649 *
 650 * note:
 651 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 652 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 653 */
 654u64 nsecs_to_jiffies64(u64 n)
 655{
 656#if (NSEC_PER_SEC % HZ) == 0
 657        /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
 658        return div_u64(n, NSEC_PER_SEC / HZ);
 659#elif (HZ % 512) == 0
 660        /* overflow after 292 years if HZ = 1024 */
 661        return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
 662#else
 663        /*
 664         * Generic case - optimized for cases where HZ is a multiple of 3.
 665         * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
 666         */
 667        return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
 668#endif
 669}
 670
 671/**
 672 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
 673 *
 674 * @n:  nsecs in u64
 675 *
 676 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 677 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 678 * for scheduler, not for use in device drivers to calculate timeout value.
 679 *
 680 * note:
 681 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 682 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 683 */
 684unsigned long nsecs_to_jiffies(u64 n)
 685{
 686        return (unsigned long)nsecs_to_jiffies64(n);
 687}
 688
 689/*
 690 * Add two timespec values and do a safety check for overflow.
 691 * It's assumed that both values are valid (>= 0)
 692 */
 693struct timespec timespec_add_safe(const struct timespec lhs,
 694                                  const struct timespec rhs)
 695{
 696        struct timespec res;
 697
 698        set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
 699                                lhs.tv_nsec + rhs.tv_nsec);
 700
 701        if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
 702                res.tv_sec = TIME_T_MAX;
 703
 704        return res;
 705}
 706
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.