Root/kernel/time.c

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    write_seqlock_irq(&xtime_lock);
136    wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
137    xtime.tv_sec += sys_tz.tz_minuteswest * 60;
138    update_xtime_cache(0);
139    write_sequnlock_irq(&xtime_lock);
140    clock_was_set();
141}
142
143/*
144 * In case for some reason the CMOS clock has not already been running
145 * in UTC, but in some local time: The first time we set the timezone,
146 * we will warp the clock so that it is ticking UTC time instead of
147 * local time. Presumably, if someone is setting the timezone then we
148 * are running in an environment where the programs understand about
149 * timezones. This should be done at boot time in the /etc/rc script,
150 * as soon as possible, so that the clock can be set right. Otherwise,
151 * various programs will get confused when the clock gets warped.
152 */
153
154int do_sys_settimeofday(struct timespec *tv, struct timezone *tz)
155{
156    static int firsttime = 1;
157    int error = 0;
158
159    if (tv && !timespec_valid(tv))
160        return -EINVAL;
161
162    error = security_settime(tv, tz);
163    if (error)
164        return error;
165
166    if (tz) {
167        /* SMP safe, global irq locking makes it work. */
168        sys_tz = *tz;
169        update_vsyscall_tz();
170        if (firsttime) {
171            firsttime = 0;
172            if (!tv)
173                warp_clock();
174        }
175    }
176    if (tv)
177    {
178        /* SMP safe, again the code in arch/foo/time.c should
179         * globally block out interrupts when it runs.
180         */
181        return do_settimeofday(tv);
182    }
183    return 0;
184}
185
186SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
187        struct timezone __user *, tz)
188{
189    struct timeval user_tv;
190    struct timespec new_ts;
191    struct timezone new_tz;
192
193    if (tv) {
194        if (copy_from_user(&user_tv, tv, sizeof(*tv)))
195            return -EFAULT;
196        new_ts.tv_sec = user_tv.tv_sec;
197        new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
198    }
199    if (tz) {
200        if (copy_from_user(&new_tz, tz, sizeof(*tz)))
201            return -EFAULT;
202    }
203
204    return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
205}
206
207SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
208{
209    struct timex txc; /* Local copy of parameter */
210    int ret;
211
212    /* Copy the user data space into the kernel copy
213     * structure. But bear in mind that the structures
214     * may change
215     */
216    if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
217        return -EFAULT;
218    ret = do_adjtimex(&txc);
219    return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
220}
221
222/**
223 * current_fs_time - Return FS time
224 * @sb: Superblock.
225 *
226 * Return the current time truncated to the time granularity supported by
227 * the fs.
228 */
229struct timespec current_fs_time(struct super_block *sb)
230{
231    struct timespec now = current_kernel_time();
232    return timespec_trunc(now, sb->s_time_gran);
233}
234EXPORT_SYMBOL(current_fs_time);
235
236/*
237 * Convert jiffies to milliseconds and back.
238 *
239 * Avoid unnecessary multiplications/divisions in the
240 * two most common HZ cases:
241 */
242unsigned int inline jiffies_to_msecs(const unsigned long j)
243{
244#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
245    return (MSEC_PER_SEC / HZ) * j;
246#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
247    return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
248#else
249# if BITS_PER_LONG == 32
250    return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
251# else
252    return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
253# endif
254#endif
255}
256EXPORT_SYMBOL(jiffies_to_msecs);
257
258unsigned int inline jiffies_to_usecs(const unsigned long j)
259{
260#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
261    return (USEC_PER_SEC / HZ) * j;
262#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
263    return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
264#else
265# if BITS_PER_LONG == 32
266    return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
267# else
268    return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
269# endif
270#endif
271}
272EXPORT_SYMBOL(jiffies_to_usecs);
273
274/**
275 * timespec_trunc - Truncate timespec to a granularity
276 * @t: Timespec
277 * @gran: Granularity in ns.
278 *
279 * Truncate a timespec to a granularity. gran must be smaller than a second.
280 * Always rounds down.
281 *
282 * This function should be only used for timestamps returned by
283 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
284 * it doesn't handle the better resolution of the latter.
285 */
286struct timespec timespec_trunc(struct timespec t, unsigned gran)
287{
288    /*
289     * Division is pretty slow so avoid it for common cases.
290     * Currently current_kernel_time() never returns better than
291     * jiffies resolution. Exploit that.
292     */
293    if (gran <= jiffies_to_usecs(1) * 1000) {
294        /* nothing */
295    } else if (gran == 1000000000) {
296        t.tv_nsec = 0;
297    } else {
298        t.tv_nsec -= t.tv_nsec % gran;
299    }
300    return t;
301}
302EXPORT_SYMBOL(timespec_trunc);
303
304#ifndef CONFIG_GENERIC_TIME
305/*
306 * Simulate gettimeofday using do_gettimeofday which only allows a timeval
307 * and therefore only yields usec accuracy
308 */
309void getnstimeofday(struct timespec *tv)
310{
311    struct timeval x;
312
313    do_gettimeofday(&x);
314    tv->tv_sec = x.tv_sec;
315    tv->tv_nsec = x.tv_usec * NSEC_PER_USEC;
316}
317EXPORT_SYMBOL_GPL(getnstimeofday);
318#endif
319
320/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
321 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
322 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
323 *
324 * [For the Julian calendar (which was used in Russia before 1917,
325 * Britain & colonies before 1752, anywhere else before 1582,
326 * and is still in use by some communities) leave out the
327 * -year/100+year/400 terms, and add 10.]
328 *
329 * This algorithm was first published by Gauss (I think).
330 *
331 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
332 * machines where long is 32-bit! (However, as time_t is signed, we
333 * will already get problems at other places on 2038-01-19 03:14:08)
334 */
335unsigned long
336mktime(const unsigned int year0, const unsigned int mon0,
337       const unsigned int day, const unsigned int hour,
338       const unsigned int min, const unsigned int sec)
339{
340    unsigned int mon = mon0, year = year0;
341
342    /* 1..12 -> 11,12,1..10 */
343    if (0 >= (int) (mon -= 2)) {
344        mon += 12; /* Puts Feb last since it has leap day */
345        year -= 1;
346    }
347
348    return ((((unsigned long)
349          (year/4 - year/100 + year/400 + 367*mon/12 + day) +
350          year*365 - 719499
351        )*24 + hour /* now have hours */
352      )*60 + min /* now have minutes */
353    )*60 + sec; /* finally seconds */
354}
355
356EXPORT_SYMBOL(mktime);
357
358/**
359 * set_normalized_timespec - set timespec sec and nsec parts and normalize
360 *
361 * @ts: pointer to timespec variable to be set
362 * @sec: seconds to set
363 * @nsec: nanoseconds to set
364 *
365 * Set seconds and nanoseconds field of a timespec variable and
366 * normalize to the timespec storage format
367 *
368 * Note: The tv_nsec part is always in the range of
369 * 0 <= tv_nsec < NSEC_PER_SEC
370 * For negative values only the tv_sec field is negative !
371 */
372void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
373{
374    while (nsec >= NSEC_PER_SEC) {
375        /*
376         * The following asm() prevents the compiler from
377         * optimising this loop into a modulo operation. See
378         * also __iter_div_u64_rem() in include/linux/time.h
379         */
380        asm("" : "+rm"(nsec));
381        nsec -= NSEC_PER_SEC;
382        ++sec;
383    }
384    while (nsec < 0) {
385        asm("" : "+rm"(nsec));
386        nsec += NSEC_PER_SEC;
387        --sec;
388    }
389    ts->tv_sec = sec;
390    ts->tv_nsec = nsec;
391}
392EXPORT_SYMBOL(set_normalized_timespec);
393
394/**
395 * ns_to_timespec - Convert nanoseconds to timespec
396 * @nsec: the nanoseconds value to be converted
397 *
398 * Returns the timespec representation of the nsec parameter.
399 */
400struct timespec ns_to_timespec(const s64 nsec)
401{
402    struct timespec ts;
403    s32 rem;
404
405    if (!nsec)
406        return (struct timespec) {0, 0};
407
408    ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
409    if (unlikely(rem < 0)) {
410        ts.tv_sec--;
411        rem += NSEC_PER_SEC;
412    }
413    ts.tv_nsec = rem;
414
415    return ts;
416}
417EXPORT_SYMBOL(ns_to_timespec);
418
419/**
420 * ns_to_timeval - Convert nanoseconds to timeval
421 * @nsec: the nanoseconds value to be converted
422 *
423 * Returns the timeval representation of the nsec parameter.
424 */
425struct timeval ns_to_timeval(const s64 nsec)
426{
427    struct timespec ts = ns_to_timespec(nsec);
428    struct timeval tv;
429
430    tv.tv_sec = ts.tv_sec;
431    tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
432
433    return tv;
434}
435EXPORT_SYMBOL(ns_to_timeval);
436
437/*
438 * When we convert to jiffies then we interpret incoming values
439 * the following way:
440 *
441 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
442 *
443 * - 'too large' values [that would result in larger than
444 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
445 *
446 * - all other values are converted to jiffies by either multiplying
447 * the input value by a factor or dividing it with a factor
448 *
449 * We must also be careful about 32-bit overflows.
450 */
451unsigned long msecs_to_jiffies(const unsigned int m)
452{
453    /*
454     * Negative value, means infinite timeout:
455     */
456    if ((int)m < 0)
457        return MAX_JIFFY_OFFSET;
458
459#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
460    /*
461     * HZ is equal to or smaller than 1000, and 1000 is a nice
462     * round multiple of HZ, divide with the factor between them,
463     * but round upwards:
464     */
465    return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
466#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
467    /*
468     * HZ is larger than 1000, and HZ is a nice round multiple of
469     * 1000 - simply multiply with the factor between them.
470     *
471     * But first make sure the multiplication result cannot
472     * overflow:
473     */
474    if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
475        return MAX_JIFFY_OFFSET;
476
477    return m * (HZ / MSEC_PER_SEC);
478#else
479    /*
480     * Generic case - multiply, round and divide. But first
481     * check that if we are doing a net multiplication, that
482     * we wouldn't overflow:
483     */
484    if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
485        return MAX_JIFFY_OFFSET;
486
487    return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
488        >> MSEC_TO_HZ_SHR32;
489#endif
490}
491EXPORT_SYMBOL(msecs_to_jiffies);
492
493unsigned long usecs_to_jiffies(const unsigned int u)
494{
495    if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
496        return MAX_JIFFY_OFFSET;
497#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
498    return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
499#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
500    return u * (HZ / USEC_PER_SEC);
501#else
502    return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
503        >> USEC_TO_HZ_SHR32;
504#endif
505}
506EXPORT_SYMBOL(usecs_to_jiffies);
507
508/*
509 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
510 * that a remainder subtract here would not do the right thing as the
511 * resolution values don't fall on second boundries. I.e. the line:
512 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
513 *
514 * Rather, we just shift the bits off the right.
515 *
516 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
517 * value to a scaled second value.
518 */
519unsigned long
520timespec_to_jiffies(const struct timespec *value)
521{
522    unsigned long sec = value->tv_sec;
523    long nsec = value->tv_nsec + TICK_NSEC - 1;
524
525    if (sec >= MAX_SEC_IN_JIFFIES){
526        sec = MAX_SEC_IN_JIFFIES;
527        nsec = 0;
528    }
529    return (((u64)sec * SEC_CONVERSION) +
530        (((u64)nsec * NSEC_CONVERSION) >>
531         (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
532
533}
534EXPORT_SYMBOL(timespec_to_jiffies);
535
536void
537jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
538{
539    /*
540     * Convert jiffies to nanoseconds and separate with
541     * one divide.
542     */
543    u32 rem;
544    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
545                    NSEC_PER_SEC, &rem);
546    value->tv_nsec = rem;
547}
548EXPORT_SYMBOL(jiffies_to_timespec);
549
550/* Same for "timeval"
551 *
552 * Well, almost. The problem here is that the real system resolution is
553 * in nanoseconds and the value being converted is in micro seconds.
554 * Also for some machines (those that use HZ = 1024, in-particular),
555 * there is a LARGE error in the tick size in microseconds.
556
557 * The solution we use is to do the rounding AFTER we convert the
558 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
559 * Instruction wise, this should cost only an additional add with carry
560 * instruction above the way it was done above.
561 */
562unsigned long
563timeval_to_jiffies(const struct timeval *value)
564{
565    unsigned long sec = value->tv_sec;
566    long usec = value->tv_usec;
567
568    if (sec >= MAX_SEC_IN_JIFFIES){
569        sec = MAX_SEC_IN_JIFFIES;
570        usec = 0;
571    }
572    return (((u64)sec * SEC_CONVERSION) +
573        (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
574         (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
575}
576EXPORT_SYMBOL(timeval_to_jiffies);
577
578void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
579{
580    /*
581     * Convert jiffies to nanoseconds and separate with
582     * one divide.
583     */
584    u32 rem;
585
586    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
587                    NSEC_PER_SEC, &rem);
588    value->tv_usec = rem / NSEC_PER_USEC;
589}
590EXPORT_SYMBOL(jiffies_to_timeval);
591
592/*
593 * Convert jiffies/jiffies_64 to clock_t and back.
594 */
595clock_t jiffies_to_clock_t(long x)
596{
597#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
598# if HZ < USER_HZ
599    return x * (USER_HZ / HZ);
600# else
601    return x / (HZ / USER_HZ);
602# endif
603#else
604    return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
605#endif
606}
607EXPORT_SYMBOL(jiffies_to_clock_t);
608
609unsigned long clock_t_to_jiffies(unsigned long x)
610{
611#if (HZ % USER_HZ)==0
612    if (x >= ~0UL / (HZ / USER_HZ))
613        return ~0UL;
614    return x * (HZ / USER_HZ);
615#else
616    /* Don't worry about loss of precision here .. */
617    if (x >= ~0UL / HZ * USER_HZ)
618        return ~0UL;
619
620    /* .. but do try to contain it here */
621    return div_u64((u64)x * HZ, USER_HZ);
622#endif
623}
624EXPORT_SYMBOL(clock_t_to_jiffies);
625
626u64 jiffies_64_to_clock_t(u64 x)
627{
628#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
629# if HZ < USER_HZ
630    x = div_u64(x * USER_HZ, HZ);
631# elif HZ > USER_HZ
632    x = div_u64(x, HZ / USER_HZ);
633# else
634    /* Nothing to do */
635# endif
636#else
637    /*
638     * There are better ways that don't overflow early,
639     * but even this doesn't overflow in hundreds of years
640     * in 64 bits, so..
641     */
642    x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
643#endif
644    return x;
645}
646EXPORT_SYMBOL(jiffies_64_to_clock_t);
647
648u64 nsec_to_clock_t(u64 x)
649{
650#if (NSEC_PER_SEC % USER_HZ) == 0
651    return div_u64(x, NSEC_PER_SEC / USER_HZ);
652#elif (USER_HZ % 512) == 0
653    return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
654#else
655    /*
656         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
657         * overflow after 64.99 years.
658         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
659         */
660    return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
661#endif
662}
663
664/**
665 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
666 *
667 * @n: nsecs in u64
668 *
669 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
670 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
671 * for scheduler, not for use in device drivers to calculate timeout value.
672 *
673 * note:
674 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
675 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
676 */
677unsigned long nsecs_to_jiffies(u64 n)
678{
679#if (NSEC_PER_SEC % HZ) == 0
680    /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
681    return div_u64(n, NSEC_PER_SEC / HZ);
682#elif (HZ % 512) == 0
683    /* overflow after 292 years if HZ = 1024 */
684    return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
685#else
686    /*
687     * Generic case - optimized for cases where HZ is a multiple of 3.
688     * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
689     */
690    return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
691#endif
692}
693
694#if (BITS_PER_LONG < 64)
695u64 get_jiffies_64(void)
696{
697    unsigned long seq;
698    u64 ret;
699
700    do {
701        seq = read_seqbegin(&xtime_lock);
702        ret = jiffies_64;
703    } while (read_seqretry(&xtime_lock, seq));
704    return ret;
705}
706EXPORT_SYMBOL(get_jiffies_64);
707#endif
708
709EXPORT_SYMBOL(jiffies);
710
711/*
712 * Add two timespec values and do a safety check for overflow.
713 * It's assumed that both values are valid (>= 0)
714 */
715struct timespec timespec_add_safe(const struct timespec lhs,
716                  const struct timespec rhs)
717{
718    struct timespec res;
719
720    set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
721                lhs.tv_nsec + rhs.tv_nsec);
722
723    if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
724        res.tv_sec = TIME_T_MAX;
725
726    return res;
727}
728

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