projects/linux·blob v3.11-rc4 · refs

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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/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}