The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/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  */
   50 struct timezone sys_tz;
   51 
   52 EXPORT_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  */
   62 SYSCALL_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 
   81 SYSCALL_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 
  101 SYSCALL_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  */
  133 static 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 
  153 int 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 
  179 SYSCALL_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 
  200 SYSCALL_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  */
  222 struct 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 }
  227 EXPORT_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  */
  235 inline 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 }
  249 EXPORT_SYMBOL(jiffies_to_msecs);
  250 
  251 inline 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 }
  265 EXPORT_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  */
  279 struct 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 }
  295 EXPORT_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  */
  312 unsigned long
  313 mktime(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 
  333 EXPORT_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  */
  349 void 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 }
  369 EXPORT_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  */
  377 struct 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 }
  394 EXPORT_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  */
  402 struct 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 }
  412 EXPORT_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  */
  428 unsigned 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 }
  468 EXPORT_SYMBOL(msecs_to_jiffies);
  469 
  470 unsigned 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 }
  483 EXPORT_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  */
  496 unsigned long
  497 timespec_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 }
  511 EXPORT_SYMBOL(timespec_to_jiffies);
  512 
  513 void
  514 jiffies_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 }
  525 EXPORT_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  */
  539 unsigned long
  540 timeval_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 }
  553 EXPORT_SYMBOL(timeval_to_jiffies);
  554 
  555 void 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 }
  567 EXPORT_SYMBOL(jiffies_to_timeval);
  568 
  569 /*
  570  * Convert jiffies/jiffies_64 to clock_t and back.
  571  */
  572 clock_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 }
  584 EXPORT_SYMBOL(jiffies_to_clock_t);
  585 
  586 unsigned 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 }
  601 EXPORT_SYMBOL(clock_t_to_jiffies);
  602 
  603 u64 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 }
  623 EXPORT_SYMBOL(jiffies_64_to_clock_t);
  624 
  625 u64 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  */
  654 u64 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  */
  684 unsigned 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  */
  693 struct 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 }

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