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/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

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