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/core.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 */
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 * Indicates if there is an offset between the system clock and the hardware
119 * clock/persistent clock/rtc.
120 */
121int persistent_clock_is_local;
122
123/*
124 * Adjust the time obtained from the CMOS to be UTC time instead of
125 * local time.
126 *
127 * This is ugly, but preferable to the alternatives. Otherwise we
128 * would either need to write a program to do it in /etc/rc (and risk
129 * confusion if the program gets run more than once; it would also be
130 * hard to make the program warp the clock precisely n hours) or
131 * compile in the timezone information into the kernel. Bad, bad....
132 *
133 * - TYT, 1992-01-01
134 *
135 * The best thing to do is to keep the CMOS clock in universal time (UTC)
136 * as real UNIX machines always do it. This avoids all headaches about
137 * daylight saving times and warping kernel clocks.
138 */
139static inline void warp_clock(void)
140{
141    if (sys_tz.tz_minuteswest != 0) {
142        struct timespec adjust;
143
144        persistent_clock_is_local = 1;
145        adjust.tv_sec = sys_tz.tz_minuteswest * 60;
146        adjust.tv_nsec = 0;
147        timekeeping_inject_offset(&adjust);
148    }
149}
150
151/*
152 * In case for some reason the CMOS clock has not already been running
153 * in UTC, but in some local time: The first time we set the timezone,
154 * we will warp the clock so that it is ticking UTC time instead of
155 * local time. Presumably, if someone is setting the timezone then we
156 * are running in an environment where the programs understand about
157 * timezones. This should be done at boot time in the /etc/rc script,
158 * as soon as possible, so that the clock can be set right. Otherwise,
159 * various programs will get confused when the clock gets warped.
160 */
161
162int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
163{
164    static int firsttime = 1;
165    int error = 0;
166
167    if (tv && !timespec_valid(tv))
168        return -EINVAL;
169
170    error = security_settime(tv, tz);
171    if (error)
172        return error;
173
174    if (tz) {
175        sys_tz = *tz;
176        update_vsyscall_tz();
177        if (firsttime) {
178            firsttime = 0;
179            if (!tv)
180                warp_clock();
181        }
182    }
183    if (tv)
184        return do_settimeofday(tv);
185    return 0;
186}
187
188SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
189        struct timezone __user *, tz)
190{
191    struct timeval user_tv;
192    struct timespec new_ts;
193    struct timezone new_tz;
194
195    if (tv) {
196        if (copy_from_user(&user_tv, tv, sizeof(*tv)))
197            return -EFAULT;
198        new_ts.tv_sec = user_tv.tv_sec;
199        new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
200    }
201    if (tz) {
202        if (copy_from_user(&new_tz, tz, sizeof(*tz)))
203            return -EFAULT;
204    }
205
206    return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
207}
208
209SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
210{
211    struct timex txc; /* Local copy of parameter */
212    int ret;
213
214    /* Copy the user data space into the kernel copy
215     * structure. But bear in mind that the structures
216     * may change
217     */
218    if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
219        return -EFAULT;
220    ret = do_adjtimex(&txc);
221    return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
222}
223
224/**
225 * current_fs_time - Return FS time
226 * @sb: Superblock.
227 *
228 * Return the current time truncated to the time granularity supported by
229 * the fs.
230 */
231struct timespec current_fs_time(struct super_block *sb)
232{
233    struct timespec now = current_kernel_time();
234    return timespec_trunc(now, sb->s_time_gran);
235}
236EXPORT_SYMBOL(current_fs_time);
237
238/*
239 * Convert jiffies to milliseconds and back.
240 *
241 * Avoid unnecessary multiplications/divisions in the
242 * two most common HZ cases:
243 */
244unsigned int jiffies_to_msecs(const unsigned long j)
245{
246#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
247    return (MSEC_PER_SEC / HZ) * j;
248#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
249    return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
250#else
251# if BITS_PER_LONG == 32
252    return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
253# else
254    return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
255# endif
256#endif
257}
258EXPORT_SYMBOL(jiffies_to_msecs);
259
260unsigned int jiffies_to_usecs(const unsigned long j)
261{
262#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
263    return (USEC_PER_SEC / HZ) * j;
264#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
265    return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
266#else
267# if BITS_PER_LONG == 32
268    return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
269# else
270    return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
271# endif
272#endif
273}
274EXPORT_SYMBOL(jiffies_to_usecs);
275
276/**
277 * timespec_trunc - Truncate timespec to a granularity
278 * @t: Timespec
279 * @gran: Granularity in ns.
280 *
281 * Truncate a timespec to a granularity. gran must be smaller than a second.
282 * Always rounds down.
283 *
284 * This function should be only used for timestamps returned by
285 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
286 * it doesn't handle the better resolution of the latter.
287 */
288struct timespec timespec_trunc(struct timespec t, unsigned gran)
289{
290    /*
291     * Division is pretty slow so avoid it for common cases.
292     * Currently current_kernel_time() never returns better than
293     * jiffies resolution. Exploit that.
294     */
295    if (gran <= jiffies_to_usecs(1) * 1000) {
296        /* nothing */
297    } else if (gran == 1000000000) {
298        t.tv_nsec = 0;
299    } else {
300        t.tv_nsec -= t.tv_nsec % gran;
301    }
302    return t;
303}
304EXPORT_SYMBOL(timespec_trunc);
305
306/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
307 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
308 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
309 *
310 * [For the Julian calendar (which was used in Russia before 1917,
311 * Britain & colonies before 1752, anywhere else before 1582,
312 * and is still in use by some communities) leave out the
313 * -year/100+year/400 terms, and add 10.]
314 *
315 * This algorithm was first published by Gauss (I think).
316 *
317 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
318 * machines where long is 32-bit! (However, as time_t is signed, we
319 * will already get problems at other places on 2038-01-19 03:14:08)
320 */
321unsigned long
322mktime(const unsigned int year0, const unsigned int mon0,
323       const unsigned int day, const unsigned int hour,
324       const unsigned int min, const unsigned int sec)
325{
326    unsigned int mon = mon0, year = year0;
327
328    /* 1..12 -> 11,12,1..10 */
329    if (0 >= (int) (mon -= 2)) {
330        mon += 12; /* Puts Feb last since it has leap day */
331        year -= 1;
332    }
333
334    return ((((unsigned long)
335          (year/4 - year/100 + year/400 + 367*mon/12 + day) +
336          year*365 - 719499
337        )*24 + hour /* now have hours */
338      )*60 + min /* now have minutes */
339    )*60 + sec; /* finally seconds */
340}
341
342EXPORT_SYMBOL(mktime);
343
344/**
345 * set_normalized_timespec - set timespec sec and nsec parts and normalize
346 *
347 * @ts: pointer to timespec variable to be set
348 * @sec: seconds to set
349 * @nsec: nanoseconds to set
350 *
351 * Set seconds and nanoseconds field of a timespec variable and
352 * normalize to the timespec storage format
353 *
354 * Note: The tv_nsec part is always in the range of
355 * 0 <= tv_nsec < NSEC_PER_SEC
356 * For negative values only the tv_sec field is negative !
357 */
358void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
359{
360    while (nsec >= NSEC_PER_SEC) {
361        /*
362         * The following asm() prevents the compiler from
363         * optimising this loop into a modulo operation. See
364         * also __iter_div_u64_rem() in include/linux/time.h
365         */
366        asm("" : "+rm"(nsec));
367        nsec -= NSEC_PER_SEC;
368        ++sec;
369    }
370    while (nsec < 0) {
371        asm("" : "+rm"(nsec));
372        nsec += NSEC_PER_SEC;
373        --sec;
374    }
375    ts->tv_sec = sec;
376    ts->tv_nsec = nsec;
377}
378EXPORT_SYMBOL(set_normalized_timespec);
379
380/**
381 * ns_to_timespec - Convert nanoseconds to timespec
382 * @nsec: the nanoseconds value to be converted
383 *
384 * Returns the timespec representation of the nsec parameter.
385 */
386struct timespec ns_to_timespec(const s64 nsec)
387{
388    struct timespec ts;
389    s32 rem;
390
391    if (!nsec)
392        return (struct timespec) {0, 0};
393
394    ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
395    if (unlikely(rem < 0)) {
396        ts.tv_sec--;
397        rem += NSEC_PER_SEC;
398    }
399    ts.tv_nsec = rem;
400
401    return ts;
402}
403EXPORT_SYMBOL(ns_to_timespec);
404
405/**
406 * ns_to_timeval - Convert nanoseconds to timeval
407 * @nsec: the nanoseconds value to be converted
408 *
409 * Returns the timeval representation of the nsec parameter.
410 */
411struct timeval ns_to_timeval(const s64 nsec)
412{
413    struct timespec ts = ns_to_timespec(nsec);
414    struct timeval tv;
415
416    tv.tv_sec = ts.tv_sec;
417    tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
418
419    return tv;
420}
421EXPORT_SYMBOL(ns_to_timeval);
422
423/*
424 * When we convert to jiffies then we interpret incoming values
425 * the following way:
426 *
427 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
428 *
429 * - 'too large' values [that would result in larger than
430 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
431 *
432 * - all other values are converted to jiffies by either multiplying
433 * the input value by a factor or dividing it with a factor
434 *
435 * We must also be careful about 32-bit overflows.
436 */
437unsigned long msecs_to_jiffies(const unsigned int m)
438{
439    /*
440     * Negative value, means infinite timeout:
441     */
442    if ((int)m < 0)
443        return MAX_JIFFY_OFFSET;
444
445#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
446    /*
447     * HZ is equal to or smaller than 1000, and 1000 is a nice
448     * round multiple of HZ, divide with the factor between them,
449     * but round upwards:
450     */
451    return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
452#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
453    /*
454     * HZ is larger than 1000, and HZ is a nice round multiple of
455     * 1000 - simply multiply with the factor between them.
456     *
457     * But first make sure the multiplication result cannot
458     * overflow:
459     */
460    if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
461        return MAX_JIFFY_OFFSET;
462
463    return m * (HZ / MSEC_PER_SEC);
464#else
465    /*
466     * Generic case - multiply, round and divide. But first
467     * check that if we are doing a net multiplication, that
468     * we wouldn't overflow:
469     */
470    if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
471        return MAX_JIFFY_OFFSET;
472
473    return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
474        >> MSEC_TO_HZ_SHR32;
475#endif
476}
477EXPORT_SYMBOL(msecs_to_jiffies);
478
479unsigned long usecs_to_jiffies(const unsigned int u)
480{
481    if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
482        return MAX_JIFFY_OFFSET;
483#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
484    return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
485#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
486    return u * (HZ / USEC_PER_SEC);
487#else
488    return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
489        >> USEC_TO_HZ_SHR32;
490#endif
491}
492EXPORT_SYMBOL(usecs_to_jiffies);
493
494/*
495 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
496 * that a remainder subtract here would not do the right thing as the
497 * resolution values don't fall on second boundries. I.e. the line:
498 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
499 *
500 * Rather, we just shift the bits off the right.
501 *
502 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
503 * value to a scaled second value.
504 */
505unsigned long
506timespec_to_jiffies(const struct timespec *value)
507{
508    unsigned long sec = value->tv_sec;
509    long nsec = value->tv_nsec + TICK_NSEC - 1;
510
511    if (sec >= MAX_SEC_IN_JIFFIES){
512        sec = MAX_SEC_IN_JIFFIES;
513        nsec = 0;
514    }
515    return (((u64)sec * SEC_CONVERSION) +
516        (((u64)nsec * NSEC_CONVERSION) >>
517         (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
518
519}
520EXPORT_SYMBOL(timespec_to_jiffies);
521
522void
523jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
524{
525    /*
526     * Convert jiffies to nanoseconds and separate with
527     * one divide.
528     */
529    u32 rem;
530    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
531                    NSEC_PER_SEC, &rem);
532    value->tv_nsec = rem;
533}
534EXPORT_SYMBOL(jiffies_to_timespec);
535
536/* Same for "timeval"
537 *
538 * Well, almost. The problem here is that the real system resolution is
539 * in nanoseconds and the value being converted is in micro seconds.
540 * Also for some machines (those that use HZ = 1024, in-particular),
541 * there is a LARGE error in the tick size in microseconds.
542
543 * The solution we use is to do the rounding AFTER we convert the
544 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
545 * Instruction wise, this should cost only an additional add with carry
546 * instruction above the way it was done above.
547 */
548unsigned long
549timeval_to_jiffies(const struct timeval *value)
550{
551    unsigned long sec = value->tv_sec;
552    long usec = value->tv_usec;
553
554    if (sec >= MAX_SEC_IN_JIFFIES){
555        sec = MAX_SEC_IN_JIFFIES;
556        usec = 0;
557    }
558    return (((u64)sec * SEC_CONVERSION) +
559        (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
560         (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
561}
562EXPORT_SYMBOL(timeval_to_jiffies);
563
564void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
565{
566    /*
567     * Convert jiffies to nanoseconds and separate with
568     * one divide.
569     */
570    u32 rem;
571
572    value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
573                    NSEC_PER_SEC, &rem);
574    value->tv_usec = rem / NSEC_PER_USEC;
575}
576EXPORT_SYMBOL(jiffies_to_timeval);
577
578/*
579 * Convert jiffies/jiffies_64 to clock_t and back.
580 */
581clock_t jiffies_to_clock_t(unsigned long x)
582{
583#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
584# if HZ < USER_HZ
585    return x * (USER_HZ / HZ);
586# else
587    return x / (HZ / USER_HZ);
588# endif
589#else
590    return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
591#endif
592}
593EXPORT_SYMBOL(jiffies_to_clock_t);
594
595unsigned long clock_t_to_jiffies(unsigned long x)
596{
597#if (HZ % USER_HZ)==0
598    if (x >= ~0UL / (HZ / USER_HZ))
599        return ~0UL;
600    return x * (HZ / USER_HZ);
601#else
602    /* Don't worry about loss of precision here .. */
603    if (x >= ~0UL / HZ * USER_HZ)
604        return ~0UL;
605
606    /* .. but do try to contain it here */
607    return div_u64((u64)x * HZ, USER_HZ);
608#endif
609}
610EXPORT_SYMBOL(clock_t_to_jiffies);
611
612u64 jiffies_64_to_clock_t(u64 x)
613{
614#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
615# if HZ < USER_HZ
616    x = div_u64(x * USER_HZ, HZ);
617# elif HZ > USER_HZ
618    x = div_u64(x, HZ / USER_HZ);
619# else
620    /* Nothing to do */
621# endif
622#else
623    /*
624     * There are better ways that don't overflow early,
625     * but even this doesn't overflow in hundreds of years
626     * in 64 bits, so..
627     */
628    x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
629#endif
630    return x;
631}
632EXPORT_SYMBOL(jiffies_64_to_clock_t);
633
634u64 nsec_to_clock_t(u64 x)
635{
636#if (NSEC_PER_SEC % USER_HZ) == 0
637    return div_u64(x, NSEC_PER_SEC / USER_HZ);
638#elif (USER_HZ % 512) == 0
639    return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
640#else
641    /*
642         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
643         * overflow after 64.99 years.
644         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
645         */
646    return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
647#endif
648}
649
650/**
651 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
652 *
653 * @n: nsecs in u64
654 *
655 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
656 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
657 * for scheduler, not for use in device drivers to calculate timeout value.
658 *
659 * note:
660 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
661 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
662 */
663u64 nsecs_to_jiffies64(u64 n)
664{
665#if (NSEC_PER_SEC % HZ) == 0
666    /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
667    return div_u64(n, NSEC_PER_SEC / HZ);
668#elif (HZ % 512) == 0
669    /* overflow after 292 years if HZ = 1024 */
670    return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
671#else
672    /*
673     * Generic case - optimized for cases where HZ is a multiple of 3.
674     * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
675     */
676    return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
677#endif
678}
679
680/**
681 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
682 *
683 * @n: nsecs in u64
684 *
685 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
686 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
687 * for scheduler, not for use in device drivers to calculate timeout value.
688 *
689 * note:
690 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
691 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
692 */
693unsigned long nsecs_to_jiffies(u64 n)
694{
695    return (unsigned long)nsecs_to_jiffies64(n);
696}
697
698/*
699 * Add two timespec values and do a safety check for overflow.
700 * It's assumed that both values are valid (>= 0)
701 */
702struct timespec timespec_add_safe(const struct timespec lhs,
703                  const struct timespec rhs)
704{
705    struct timespec res;
706
707    set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
708                lhs.tv_nsec + rhs.tv_nsec);
709
710    if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
711        res.tv_sec = TIME_T_MAX;
712
713    return res;
714}
715

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