projects/linux·blob v3.9-rc6 · 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.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 struct timespec adjust;
142
143 adjust = current_kernel_time();
144 if (sys_tz.tz_minuteswest != 0)
145 persistent_clock_is_local = 1;
146 adjust.tv_sec += sys_tz.tz_minuteswest * 60;
147 do_settimeofday(&adjust);
148}
149
150/*
151 * In case for some reason the CMOS clock has not already been running
152 * in UTC, but in some local time: The first time we set the timezone,
153 * we will warp the clock so that it is ticking UTC time instead of
154 * local time. Presumably, if someone is setting the timezone then we
155 * are running in an environment where the programs understand about
156 * timezones. This should be done at boot time in the /etc/rc script,
157 * as soon as possible, so that the clock can be set right. Otherwise,
158 * various programs will get confused when the clock gets warped.
159 */
160
161int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
162{
163 static int firsttime = 1;
164 int error = 0;
165
166 if (tv && !timespec_valid(tv))
167 return -EINVAL;
168
169 error = security_settime(tv, tz);
170 if (error)
171 return error;
172
173 if (tz) {
174 sys_tz = *tz;
175 update_vsyscall_tz();
176 if (firsttime) {
177 firsttime = 0;
178 if (!tv)
179 warp_clock();
180 }
181 }
182 if (tv)
183 return do_settimeofday(tv);
184 return 0;
185}
186
187SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
188 struct timezone __user *, tz)
189{
190 struct timeval user_tv;
191 struct timespec new_ts;
192 struct timezone new_tz;
193
194 if (tv) {
195 if (copy_from_user(&user_tv, tv, sizeof(*tv)))
196 return -EFAULT;
197 new_ts.tv_sec = user_tv.tv_sec;
198 new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
199 }
200 if (tz) {
201 if (copy_from_user(&new_tz, tz, sizeof(*tz)))
202 return -EFAULT;
203 }
204
205 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
206}
207
208SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
209{
210 struct timex txc; /* Local copy of parameter */
211 int ret;
212
213 /* Copy the user data space into the kernel copy
214 * structure. But bear in mind that the structures
215 * may change
216 */
217 if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
218 return -EFAULT;
219 ret = do_adjtimex(&txc);
220 return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
221}
222
223/**
224 * current_fs_time - Return FS time
225 * @sb: Superblock.
226 *
227 * Return the current time truncated to the time granularity supported by
228 * the fs.
229 */
230struct timespec current_fs_time(struct super_block *sb)
231{
232 struct timespec now = current_kernel_time();
233 return timespec_trunc(now, sb->s_time_gran);
234}
235EXPORT_SYMBOL(current_fs_time);
236
237/*
238 * Convert jiffies to milliseconds and back.
239 *
240 * Avoid unnecessary multiplications/divisions in the
241 * two most common HZ cases:
242 */
243unsigned int jiffies_to_msecs(const unsigned long j)
244{
245#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
246 return (MSEC_PER_SEC / HZ) * j;
247#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
248 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
249#else
250# if BITS_PER_LONG == 32
251 return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
252# else
253 return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
254# endif
255#endif
256}
257EXPORT_SYMBOL(jiffies_to_msecs);
258
259unsigned int jiffies_to_usecs(const unsigned long j)
260{
261#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
262 return (USEC_PER_SEC / HZ) * j;
263#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
264 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
265#else
266# if BITS_PER_LONG == 32
267 return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
268# else
269 return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
270# endif
271#endif
272}
273EXPORT_SYMBOL(jiffies_to_usecs);
274
275/**
276 * timespec_trunc - Truncate timespec to a granularity
277 * @t: Timespec
278 * @gran: Granularity in ns.
279 *
280 * Truncate a timespec to a granularity. gran must be smaller than a second.
281 * Always rounds down.
282 *
283 * This function should be only used for timestamps returned by
284 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
285 * it doesn't handle the better resolution of the latter.
286 */
287struct timespec timespec_trunc(struct timespec t, unsigned gran)
288{
289 /*
290 * Division is pretty slow so avoid it for common cases.
291 * Currently current_kernel_time() never returns better than
292 * jiffies resolution. Exploit that.
293 */
294 if (gran <= jiffies_to_usecs(1) * 1000) {
295 /* nothing */
296 } else if (gran == 1000000000) {
297 t.tv_nsec = 0;
298 } else {
299 t.tv_nsec -= t.tv_nsec % gran;
300 }
301 return t;
302}
303EXPORT_SYMBOL(timespec_trunc);
304
305/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
306 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
307 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
308 *
309 * [For the Julian calendar (which was used in Russia before 1917,
310 * Britain & colonies before 1752, anywhere else before 1582,
311 * and is still in use by some communities) leave out the
312 * -year/100+year/400 terms, and add 10.]
313 *
314 * This algorithm was first published by Gauss (I think).
315 *
316 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
317 * machines where long is 32-bit! (However, as time_t is signed, we
318 * will already get problems at other places on 2038-01-19 03:14:08)
319 */
320unsigned long
321mktime(const unsigned int year0, const unsigned int mon0,
322 const unsigned int day, const unsigned int hour,
323 const unsigned int min, const unsigned int sec)
324{
325 unsigned int mon = mon0, year = year0;
326
327 /* 1..12 -> 11,12,1..10 */
328 if (0 >= (int) (mon -= 2)) {
329 mon += 12; /* Puts Feb last since it has leap day */
330 year -= 1;
331 }
332
333 return ((((unsigned long)
334 (year/4 - year/100 + year/400 + 367*mon/12 + day) +
335 year*365 - 719499
336 )*24 + hour /* now have hours */
337 )*60 + min /* now have minutes */
338 )*60 + sec; /* finally seconds */
339}
340
341EXPORT_SYMBOL(mktime);
342
343/**
344 * set_normalized_timespec - set timespec sec and nsec parts and normalize
345 *
346 * @ts: pointer to timespec variable to be set
347 * @sec: seconds to set
348 * @nsec: nanoseconds to set
349 *
350 * Set seconds and nanoseconds field of a timespec variable and
351 * normalize to the timespec storage format
352 *
353 * Note: The tv_nsec part is always in the range of
354 * 0 <= tv_nsec < NSEC_PER_SEC
355 * For negative values only the tv_sec field is negative !
356 */
357void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
358{
359 while (nsec >= NSEC_PER_SEC) {
360 /*
361 * The following asm() prevents the compiler from
362 * optimising this loop into a modulo operation. See
363 * also __iter_div_u64_rem() in include/linux/time.h
364 */
365 asm("" : "+rm"(nsec));
366 nsec -= NSEC_PER_SEC;
367 ++sec;
368 }
369 while (nsec < 0) {
370 asm("" : "+rm"(nsec));
371 nsec += NSEC_PER_SEC;
372 --sec;
373 }
374 ts->tv_sec = sec;
375 ts->tv_nsec = nsec;
376}
377EXPORT_SYMBOL(set_normalized_timespec);
378
379/**
380 * ns_to_timespec - Convert nanoseconds to timespec
381 * @nsec: the nanoseconds value to be converted
382 *
383 * Returns the timespec representation of the nsec parameter.
384 */
385struct timespec ns_to_timespec(const s64 nsec)
386{
387 struct timespec ts;
388 s32 rem;
389
390 if (!nsec)
391 return (struct timespec) {0, 0};
392
393 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
394 if (unlikely(rem < 0)) {
395 ts.tv_sec--;
396 rem += NSEC_PER_SEC;
397 }
398 ts.tv_nsec = rem;
399
400 return ts;
401}
402EXPORT_SYMBOL(ns_to_timespec);
403
404/**
405 * ns_to_timeval - Convert nanoseconds to timeval
406 * @nsec: the nanoseconds value to be converted
407 *
408 * Returns the timeval representation of the nsec parameter.
409 */
410struct timeval ns_to_timeval(const s64 nsec)
411{
412 struct timespec ts = ns_to_timespec(nsec);
413 struct timeval tv;
414
415 tv.tv_sec = ts.tv_sec;
416 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
417
418 return tv;
419}
420EXPORT_SYMBOL(ns_to_timeval);
421
422/*
423 * When we convert to jiffies then we interpret incoming values
424 * the following way:
425 *
426 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
427 *
428 * - 'too large' values [that would result in larger than
429 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
430 *
431 * - all other values are converted to jiffies by either multiplying
432 * the input value by a factor or dividing it with a factor
433 *
434 * We must also be careful about 32-bit overflows.
435 */
436unsigned long msecs_to_jiffies(const unsigned int m)
437{
438 /*
439 * Negative value, means infinite timeout:
440 */
441 if ((int)m < 0)
442 return MAX_JIFFY_OFFSET;
443
444#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
445 /*
446 * HZ is equal to or smaller than 1000, and 1000 is a nice
447 * round multiple of HZ, divide with the factor between them,
448 * but round upwards:
449 */
450 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
451#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
452 /*
453 * HZ is larger than 1000, and HZ is a nice round multiple of
454 * 1000 - simply multiply with the factor between them.
455 *
456 * But first make sure the multiplication result cannot
457 * overflow:
458 */
459 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
460 return MAX_JIFFY_OFFSET;
461
462 return m * (HZ / MSEC_PER_SEC);
463#else
464 /*
465 * Generic case - multiply, round and divide. But first
466 * check that if we are doing a net multiplication, that
467 * we wouldn't overflow:
468 */
469 if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
470 return MAX_JIFFY_OFFSET;
471
472 return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
473 >> MSEC_TO_HZ_SHR32;
474#endif
475}
476EXPORT_SYMBOL(msecs_to_jiffies);
477
478unsigned long usecs_to_jiffies(const unsigned int u)
479{
480 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
481 return MAX_JIFFY_OFFSET;
482#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
483 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
484#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
485 return u * (HZ / USEC_PER_SEC);
486#else
487 return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
488 >> USEC_TO_HZ_SHR32;
489#endif
490}
491EXPORT_SYMBOL(usecs_to_jiffies);
492
493/*
494 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
495 * that a remainder subtract here would not do the right thing as the
496 * resolution values don't fall on second boundries. I.e. the line:
497 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
498 *
499 * Rather, we just shift the bits off the right.
500 *
501 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
502 * value to a scaled second value.
503 */
504unsigned long
505timespec_to_jiffies(const struct timespec *value)
506{
507 unsigned long sec = value->tv_sec;
508 long nsec = value->tv_nsec + TICK_NSEC - 1;
509
510 if (sec >= MAX_SEC_IN_JIFFIES){
511 sec = MAX_SEC_IN_JIFFIES;
512 nsec = 0;
513 }
514 return (((u64)sec * SEC_CONVERSION) +
515 (((u64)nsec * NSEC_CONVERSION) >>
516 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
517
518}
519EXPORT_SYMBOL(timespec_to_jiffies);
520
521void
522jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
523{
524 /*
525 * Convert jiffies to nanoseconds and separate with
526 * one divide.
527 */
528 u32 rem;
529 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
530 NSEC_PER_SEC, &rem);
531 value->tv_nsec = rem;
532}
533EXPORT_SYMBOL(jiffies_to_timespec);
534
535/* Same for "timeval"
536 *
537 * Well, almost. The problem here is that the real system resolution is
538 * in nanoseconds and the value being converted is in micro seconds.
539 * Also for some machines (those that use HZ = 1024, in-particular),
540 * there is a LARGE error in the tick size in microseconds.
541
542 * The solution we use is to do the rounding AFTER we convert the
543 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
544 * Instruction wise, this should cost only an additional add with carry
545 * instruction above the way it was done above.
546 */
547unsigned long
548timeval_to_jiffies(const struct timeval *value)
549{
550 unsigned long sec = value->tv_sec;
551 long usec = value->tv_usec;
552
553 if (sec >= MAX_SEC_IN_JIFFIES){
554 sec = MAX_SEC_IN_JIFFIES;
555 usec = 0;
556 }
557 return (((u64)sec * SEC_CONVERSION) +
558 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
559 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
560}
561EXPORT_SYMBOL(timeval_to_jiffies);
562
563void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
564{
565 /*
566 * Convert jiffies to nanoseconds and separate with
567 * one divide.
568 */
569 u32 rem;
570
571 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
572 NSEC_PER_SEC, &rem);
573 value->tv_usec = rem / NSEC_PER_USEC;
574}
575EXPORT_SYMBOL(jiffies_to_timeval);
576
577/*
578 * Convert jiffies/jiffies_64 to clock_t and back.
579 */
580clock_t jiffies_to_clock_t(unsigned long x)
581{
582#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
583# if HZ < USER_HZ
584 return x * (USER_HZ / HZ);
585# else
586 return x / (HZ / USER_HZ);
587# endif
588#else
589 return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
590#endif
591}
592EXPORT_SYMBOL(jiffies_to_clock_t);
593
594unsigned long clock_t_to_jiffies(unsigned long x)
595{
596#if (HZ % USER_HZ)==0
597 if (x >= ~0UL / (HZ / USER_HZ))
598 return ~0UL;
599 return x * (HZ / USER_HZ);
600#else
601 /* Don't worry about loss of precision here .. */
602 if (x >= ~0UL / HZ * USER_HZ)
603 return ~0UL;
604
605 /* .. but do try to contain it here */
606 return div_u64((u64)x * HZ, USER_HZ);
607#endif
608}
609EXPORT_SYMBOL(clock_t_to_jiffies);
610
611u64 jiffies_64_to_clock_t(u64 x)
612{
613#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
614# if HZ < USER_HZ
615 x = div_u64(x * USER_HZ, HZ);
616# elif HZ > USER_HZ
617 x = div_u64(x, HZ / USER_HZ);
618# else
619 /* Nothing to do */
620# endif
621#else
622 /*
623 * There are better ways that don't overflow early,
624 * but even this doesn't overflow in hundreds of years
625 * in 64 bits, so..
626 */
627 x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
628#endif
629 return x;
630}
631EXPORT_SYMBOL(jiffies_64_to_clock_t);
632
633u64 nsec_to_clock_t(u64 x)
634{
635#if (NSEC_PER_SEC % USER_HZ) == 0
636 return div_u64(x, NSEC_PER_SEC / USER_HZ);
637#elif (USER_HZ % 512) == 0
638 return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
639#else
640 /*
641 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
642 * overflow after 64.99 years.
643 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
644 */
645 return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
646#endif
647}
648
649/**
650 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
651 *
652 * @n: nsecs in u64
653 *
654 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
655 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
656 * for scheduler, not for use in device drivers to calculate timeout value.
657 *
658 * note:
659 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
660 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
661 */
662u64 nsecs_to_jiffies64(u64 n)
663{
664#if (NSEC_PER_SEC % HZ) == 0
665 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
666 return div_u64(n, NSEC_PER_SEC / HZ);
667#elif (HZ % 512) == 0
668 /* overflow after 292 years if HZ = 1024 */
669 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
670#else
671 /*
672 * Generic case - optimized for cases where HZ is a multiple of 3.
673 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
674 */
675 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
676#endif
677}
678
679/**
680 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
681 *
682 * @n: nsecs in u64
683 *
684 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
685 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
686 * for scheduler, not for use in device drivers to calculate timeout value.
687 *
688 * note:
689 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
690 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
691 */
692unsigned long nsecs_to_jiffies(u64 n)
693{
694 return (unsigned long)nsecs_to_jiffies64(n);
695}
696
697/*
698 * Add two timespec values and do a safety check for overflow.
699 * It's assumed that both values are valid (>= 0)
700 */
701struct timespec timespec_add_safe(const struct timespec lhs,
702 const struct timespec rhs)
703{
704 struct timespec res;
705
706 set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
707 lhs.tv_nsec + rhs.tv_nsec);
708
709 if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
710 res.tv_sec = TIME_T_MAX;
711
712 return res;
713}