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    struct timespec adjust;
136
137    adjust = current_kernel_time();
138    adjust.tv_sec += sys_tz.tz_minuteswest * 60;
139    do_settimeofday(&adjust);
140}
141
142/*
143 * In case for some reason the CMOS clock has not already been running
144 * in UTC, but in some local time: The first time we set the timezone,
145 * we will warp the clock so that it is ticking UTC time instead of
146 * local time. Presumably, if someone is setting the timezone then we
147 * are running in an environment where the programs understand about
148 * timezones. This should be done at boot time in the /etc/rc script,
149 * as soon as possible, so that the clock can be set right. Otherwise,
150 * various programs will get confused when the clock gets warped.
151 */
152
153int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
154{
155    static int firsttime = 1;
156    int error = 0;
157
158    if (tv && !timespec_valid(tv))
159        return -EINVAL;
160
161    error = security_settime(tv, tz);
162    if (error)
163        return error;
164
165    if (tz) {
166        /* SMP safe, global irq locking makes it work. */
167        sys_tz = *tz;
168        update_vsyscall_tz();
169        if (firsttime) {
170            firsttime = 0;
171            if (!tv)
172                warp_clock();
173        }
174    }
175    if (tv)
176    {
177        /* SMP safe, again the code in arch/foo/time.c should
178         * globally block out interrupts when it runs.
179         */
180        return do_settimeofday(tv);
181    }
182    return 0;
183}
184
185SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
186        struct timezone __user *, tz)
187{
188    struct timeval user_tv;
189    struct timespec new_ts;
190    struct timezone new_tz;
191
192    if (tv) {
193        if (copy_from_user(&user_tv, tv, sizeof(*tv)))
194            return -EFAULT;
195        new_ts.tv_sec = user_tv.tv_sec;
196        new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
197    }
198    if (tz) {
199        if (copy_from_user(&new_tz, tz, sizeof(*tz)))
200            return -EFAULT;
201    }
202
203    return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
204}
205
206SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
207{
208    struct timex txc; /* Local copy of parameter */
209    int ret;
210
211    /* Copy the user data space into the kernel copy
212     * structure. But bear in mind that the structures
213     * may change
214     */
215    if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
216        return -EFAULT;
217    ret = do_adjtimex(&txc);
218    return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
219}
220
221/**
222 * current_fs_time - Return FS time
223 * @sb: Superblock.
224 *
225 * Return the current time truncated to the time granularity supported by
226 * the fs.
227 */
228struct timespec current_fs_time(struct super_block *sb)
229{
230    struct timespec now = current_kernel_time();
231    return timespec_trunc(now, sb->s_time_gran);
232}
233EXPORT_SYMBOL(current_fs_time);
234
235/*
236 * Convert jiffies to milliseconds and back.
237 *
238 * Avoid unnecessary multiplications/divisions in the
239 * two most common HZ cases:
240 */
241inline unsigned int jiffies_to_msecs(const unsigned long j)
242{
243#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
244    return (MSEC_PER_SEC / HZ) * j;
245#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
246    return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
247#else
248# if BITS_PER_LONG == 32
249    return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
250# else
251    return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
252# endif
253#endif
254}
255EXPORT_SYMBOL(jiffies_to_msecs);
256
257inline unsigned int jiffies_to_usecs(const unsigned long j)
258{
259#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
260    return (USEC_PER_SEC / HZ) * j;
261#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
262    return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
263#else
264# if BITS_PER_LONG == 32
265    return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
266# else
267    return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
268# endif
269#endif
270}
271EXPORT_SYMBOL(jiffies_to_usecs);
272
273/**
274 * timespec_trunc - Truncate timespec to a granularity
275 * @t: Timespec
276 * @gran: Granularity in ns.
277 *
278 * Truncate a timespec to a granularity. gran must be smaller than a second.
279 * Always rounds down.
280 *
281 * This function should be only used for timestamps returned by
282 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
283 * it doesn't handle the better resolution of the latter.
284 */
285struct timespec timespec_trunc(struct timespec t, unsigned gran)
286{
287    /*
288     * Division is pretty slow so avoid it for common cases.
289     * Currently current_kernel_time() never returns better than
290     * jiffies resolution. Exploit that.
291     */
292    if (gran <= jiffies_to_usecs(1) * 1000) {
293        /* nothing */
294    } else if (gran == 1000000000) {
295        t.tv_nsec = 0;
296    } else {
297        t.tv_nsec -= t.tv_nsec % gran;
298    }
299    return t;
300}
301EXPORT_SYMBOL(timespec_trunc);
302
303/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
304 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
305 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
306 *
307 * [For the Julian calendar (which was used in Russia before 1917,
308 * Britain & colonies before 1752, anywhere else before 1582,
309 * and is still in use by some communities) leave out the
310 * -year/100+year/400 terms, and add 10.]
311 *
312 * This algorithm was first published by Gauss (I think).
313 *
314 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
315 * machines where long is 32-bit! (However, as time_t is signed, we
316 * will already get problems at other places on 2038-01-19 03:14:08)
317 */
318unsigned long
319mktime(const unsigned int year0, const unsigned int mon0,
320       const unsigned int day, const unsigned int hour,
321       const unsigned int min, const unsigned int sec)
322{
323    unsigned int mon = mon0, year = year0;
324
325    /* 1..12 -> 11,12,1..10 */
326    if (0 >= (int) (mon -= 2)) {
327        mon += 12; /* Puts Feb last since it has leap day */
328        year -= 1;
329    }
330
331    return ((((unsigned long)
332          (year/4 - year/100 + year/400 + 367*mon/12 + day) +
333          year*365 - 719499
334        )*24 + hour /* now have hours */
335      )*60 + min /* now have minutes */
336    )*60 + sec; /* finally seconds */
337}
338
339EXPORT_SYMBOL(mktime);
340
341/**
342 * set_normalized_timespec - set timespec sec and nsec parts and normalize
343 *
344 * @ts: pointer to timespec variable to be set
345 * @sec: seconds to set
346 * @nsec: nanoseconds to set
347 *
348 * Set seconds and nanoseconds field of a timespec variable and
349 * normalize to the timespec storage format
350 *
351 * Note: The tv_nsec part is always in the range of
352 * 0 <= tv_nsec < NSEC_PER_SEC
353 * For negative values only the tv_sec field is negative !
354 */
355void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
356{
357    while (nsec >= NSEC_PER_SEC) {
358        /*
359         * The following asm() prevents the compiler from
360         * optimising this loop into a modulo operation. See
361         * also __iter_div_u64_rem() in include/linux/time.h
362         */
363        asm("" : "+rm"(nsec));
364        nsec -= NSEC_PER_SEC;
365        ++sec;
366    }
367    while (nsec < 0) {
368        asm("" : "+rm"(nsec));
369        nsec += NSEC_PER_SEC;
370        --sec;
371    }
372    ts->tv_sec = sec;
373    ts->tv_nsec = nsec;
374}
375EXPORT_SYMBOL(set_normalized_timespec);
376
377/**
378 * ns_to_timespec - Convert nanoseconds to timespec
379 * @nsec: the nanoseconds value to be converted
380 *
381 * Returns the timespec representation of the nsec parameter.
382 */
383struct timespec ns_to_timespec(const s64 nsec)
384{
385    struct timespec ts;
386    s32 rem;
387
388    if (!nsec)
389        return (struct timespec) {0, 0};
390
391    ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
392    if (unlikely(rem < 0)) {
393        ts.tv_sec--;
394        rem += NSEC_PER_SEC;
395    }
396    ts.tv_nsec = rem;
397
398    return ts;
399}
400EXPORT_SYMBOL(ns_to_timespec);
401
402/**
403 * ns_to_timeval - Convert nanoseconds to timeval
404 * @nsec: the nanoseconds value to be converted
405 *
406 * Returns the timeval representation of the nsec parameter.
407 */
408struct timeval ns_to_timeval(const s64 nsec)
409{
410    struct timespec ts = ns_to_timespec(nsec);
411    struct timeval tv;
412
413    tv.tv_sec = ts.tv_sec;
414    tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
415
416    return tv;
417}
418EXPORT_SYMBOL(ns_to_timeval);
419
420/*
421 * When we convert to jiffies then we interpret incoming values
422 * the following way:
423 *
424 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
425 *
426 * - 'too large' values [that would result in larger than
427 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
428 *
429 * - all other values are converted to jiffies by either multiplying
430 * the input value by a factor or dividing it with a factor
431 *
432 * We must also be careful about 32-bit overflows.
433 */
434unsigned long msecs_to_jiffies(const unsigned int m)
435{
436    /*
437     * Negative value, means infinite timeout:
438     */
439    if ((int)m < 0)
440        return MAX_JIFFY_OFFSET;
441
442#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
443    /*
444     * HZ is equal to or smaller than 1000, and 1000 is a nice
445     * round multiple of HZ, divide with the factor between them,
446     * but round upwards:
447     */
448    return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
449#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
450    /*
451     * HZ is larger than 1000, and HZ is a nice round multiple of
452     * 1000 - simply multiply with the factor between them.
453     *
454     * But first make sure the multiplication result cannot
455     * overflow:
456     */
457    if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
458        return MAX_JIFFY_OFFSET;
459
460    return m * (HZ / MSEC_PER_SEC);
461#else
462    /*
463     * Generic case - multiply, round and divide. But first
464     * check that if we are doing a net multiplication, that
465     * we wouldn't overflow:
466     */
467    if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
468        return MAX_JIFFY_OFFSET;
469
470    return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
471        >> MSEC_TO_HZ_SHR32;
472#endif
473}
474EXPORT_SYMBOL(msecs_to_jiffies);
475
476unsigned long usecs_to_jiffies(const unsigned int u)
477{
478    if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
479        return MAX_JIFFY_OFFSET;
480#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
481    return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
482#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
483    return u * (HZ / USEC_PER_SEC);
484#else
485    return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
486        >> USEC_TO_HZ_SHR32;
487#endif
488}
489EXPORT_SYMBOL(usecs_to_jiffies);
490
491/*
492 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
493 * that a remainder subtract here would not do the right thing as the
494 * resolution values don't fall on second boundries. I.e. the line:
495 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
496 *
497 * Rather, we just shift the bits off the right.
498 *
499 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
500 * value to a scaled second value.
501 */
502unsigned long
503timespec_to_jiffies(const struct timespec *value)
504{
505    unsigned long sec = value->tv_sec;
506    long nsec = value->tv_nsec + TICK_NSEC - 1;
507
508    if (sec >= MAX_SEC_IN_JIFFIES){
509        sec = MAX_SEC_IN_JIFFIES;
510        nsec = 0;
511    }
512    return (((u64)sec * SEC_CONVERSION) +
513        (((u64)nsec * NSEC_CONVERSION) >>
514         (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
515
516}
517EXPORT_SYMBOL(timespec_to_jiffies);
518
519void
520jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
521{
522    /*
523     * Convert jiffies to nanoseconds and separate with
524     * one divide.
525     */
526    u32 rem;
527    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
528                    NSEC_PER_SEC, &rem);
529    value->tv_nsec = rem;
530}
531EXPORT_SYMBOL(jiffies_to_timespec);
532
533/* Same for "timeval"
534 *
535 * Well, almost. The problem here is that the real system resolution is
536 * in nanoseconds and the value being converted is in micro seconds.
537 * Also for some machines (those that use HZ = 1024, in-particular),
538 * there is a LARGE error in the tick size in microseconds.
539
540 * The solution we use is to do the rounding AFTER we convert the
541 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
542 * Instruction wise, this should cost only an additional add with carry
543 * instruction above the way it was done above.
544 */
545unsigned long
546timeval_to_jiffies(const struct timeval *value)
547{
548    unsigned long sec = value->tv_sec;
549    long usec = value->tv_usec;
550
551    if (sec >= MAX_SEC_IN_JIFFIES){
552        sec = MAX_SEC_IN_JIFFIES;
553        usec = 0;
554    }
555    return (((u64)sec * SEC_CONVERSION) +
556        (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
557         (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
558}
559EXPORT_SYMBOL(timeval_to_jiffies);
560
561void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
562{
563    /*
564     * Convert jiffies to nanoseconds and separate with
565     * one divide.
566     */
567    u32 rem;
568
569    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
570                    NSEC_PER_SEC, &rem);
571    value->tv_usec = rem / NSEC_PER_USEC;
572}
573EXPORT_SYMBOL(jiffies_to_timeval);
574
575/*
576 * Convert jiffies/jiffies_64 to clock_t and back.
577 */
578clock_t jiffies_to_clock_t(long x)
579{
580#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
581# if HZ < USER_HZ
582    return x * (USER_HZ / HZ);
583# else
584    return x / (HZ / USER_HZ);
585# endif
586#else
587    return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
588#endif
589}
590EXPORT_SYMBOL(jiffies_to_clock_t);
591
592unsigned long clock_t_to_jiffies(unsigned long x)
593{
594#if (HZ % USER_HZ)==0
595    if (x >= ~0UL / (HZ / USER_HZ))
596        return ~0UL;
597    return x * (HZ / USER_HZ);
598#else
599    /* Don't worry about loss of precision here .. */
600    if (x >= ~0UL / HZ * USER_HZ)
601        return ~0UL;
602
603    /* .. but do try to contain it here */
604    return div_u64((u64)x * HZ, USER_HZ);
605#endif
606}
607EXPORT_SYMBOL(clock_t_to_jiffies);
608
609u64 jiffies_64_to_clock_t(u64 x)
610{
611#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
612# if HZ < USER_HZ
613    x = div_u64(x * USER_HZ, HZ);
614# elif HZ > USER_HZ
615    x = div_u64(x, HZ / USER_HZ);
616# else
617    /* Nothing to do */
618# endif
619#else
620    /*
621     * There are better ways that don't overflow early,
622     * but even this doesn't overflow in hundreds of years
623     * in 64 bits, so..
624     */
625    x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
626#endif
627    return x;
628}
629EXPORT_SYMBOL(jiffies_64_to_clock_t);
630
631u64 nsec_to_clock_t(u64 x)
632{
633#if (NSEC_PER_SEC % USER_HZ) == 0
634    return div_u64(x, NSEC_PER_SEC / USER_HZ);
635#elif (USER_HZ % 512) == 0
636    return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
637#else
638    /*
639         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
640         * overflow after 64.99 years.
641         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
642         */
643    return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
644#endif
645}
646
647/**
648 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
649 *
650 * @n: nsecs in u64
651 *
652 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
653 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
654 * for scheduler, not for use in device drivers to calculate timeout value.
655 *
656 * note:
657 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
658 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
659 */
660u64 nsecs_to_jiffies64(u64 n)
661{
662#if (NSEC_PER_SEC % HZ) == 0
663    /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
664    return div_u64(n, NSEC_PER_SEC / HZ);
665#elif (HZ % 512) == 0
666    /* overflow after 292 years if HZ = 1024 */
667    return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
668#else
669    /*
670     * Generic case - optimized for cases where HZ is a multiple of 3.
671     * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
672     */
673    return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
674#endif
675}
676
677/**
678 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
679 *
680 * @n: nsecs in u64
681 *
682 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
683 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
684 * for scheduler, not for use in device drivers to calculate timeout value.
685 *
686 * note:
687 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
688 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
689 */
690unsigned long nsecs_to_jiffies(u64 n)
691{
692    return (unsigned long)nsecs_to_jiffies64(n);
693}
694
695/*
696 * Add two timespec values and do a safety check for overflow.
697 * It's assumed that both values are valid (>= 0)
698 */
699struct timespec timespec_add_safe(const struct timespec lhs,
700                  const struct timespec rhs)
701{
702    struct timespec res;
703
704    set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
705                lhs.tv_nsec + rhs.tv_nsec);
706
707    if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
708        res.tv_sec = TIME_T_MAX;
709
710    return res;
711}
712

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