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 */
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>
41 #include <asm/uaccess.h>
42 #include <asm/unistd.h>
44 #include "timeconst.h"
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 */
50 struct timezone sys_tz;
52 EXPORT_SYMBOL(sys_tz);
54 #ifdef __ARCH_WANT_SYS_TIME
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 */
62 SYSCALL_DEFINE1(time, time_t __user *, tloc)
63 {
64 time_t i = get_seconds();
66 if (tloc) {
67 if (put_user(i,tloc))
68 return -EFAULT;
69 }
70 force_successful_syscall_return();
71 return i;
72 }
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 */
81 SYSCALL_DEFINE1(stime, time_t __user *, tptr)
82 {
83 struct timespec tv;
84 int err;
86 if (get_user(tv.tv_sec, tptr))
87 return -EFAULT;
89 tv.tv_nsec = 0;
91 err = security_settime(&tv, NULL);
92 if (err)
93 return err;
95 do_settimeofday(&tv);
96 return 0;
97 }
99 #endif /* __ARCH_WANT_SYS_TIME */
101 SYSCALL_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 }
117 /*
118 * Indicates if there is an offset between the system clock and the hardware
119 * clock/persistent clock/rtc.
120 */
121 int persistent_clock_is_local;
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 */
139 static inline void warp_clock(void)
140 {
141 if (sys_tz.tz_minuteswest != 0) {
142 struct timespec adjust;
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 }
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 */
162 int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
163 {
164 static int firsttime = 1;
165 int error = 0;
167 if (tv && !timespec_valid(tv))
168 return -EINVAL;
170 error = security_settime(tv, tz);
171 if (error)
172 return error;
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 }
188 SYSCALL_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;
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 }
206 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
207 }
209 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
210 {
211 struct timex txc; /* Local copy of parameter */
212 int ret;
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 }
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 */
231 struct 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 }
236 EXPORT_SYMBOL(current_fs_time);
238 /*
239 * Convert jiffies to milliseconds and back.
240 *
241 * Avoid unnecessary multiplications/divisions in the
242 * two most common HZ cases:
243 */
244 unsigned 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 }
258 EXPORT_SYMBOL(jiffies_to_msecs);
260 unsigned 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 }
274 EXPORT_SYMBOL(jiffies_to_usecs);
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 */
288 struct 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 }
304 EXPORT_SYMBOL(timespec_trunc);
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 */
321 unsigned long
322 mktime(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;
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 }
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 }
342 EXPORT_SYMBOL(mktime);
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 */
358 void 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 }
378 EXPORT_SYMBOL(set_normalized_timespec);
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 */
386 struct timespec ns_to_timespec(const s64 nsec)
387 {
388 struct timespec ts;
389 s32 rem;
391 if (!nsec)
392 return (struct timespec) {0, 0};
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;
401 return ts;
402 }
403 EXPORT_SYMBOL(ns_to_timespec);
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 */
411 struct timeval ns_to_timeval(const s64 nsec)
412 {
413 struct timespec ts = ns_to_timespec(nsec);
414 struct timeval tv;
416 tv.tv_sec = ts.tv_sec;
417 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
419 return tv;
420 }
421 EXPORT_SYMBOL(ns_to_timeval);
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 */
437 unsigned 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;
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;
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;
473 return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
474 >> MSEC_TO_HZ_SHR32;
475 #endif
476 }
477 EXPORT_SYMBOL(msecs_to_jiffies);
479 unsigned 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 }
492 EXPORT_SYMBOL(usecs_to_jiffies);
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 * Note that due to the small error in the multiplier here, this
500 * rounding is incorrect for sufficiently large values of tv_nsec, but
501 * well formed timespecs should have tv_nsec < NSEC_PER_SEC, so we're
502 * OK.
503 *
504 * Rather, we just shift the bits off the right.
505 *
506 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
507 * value to a scaled second value.
508 */
509 static unsigned long
510 __timespec_to_jiffies(unsigned long sec, long nsec)
511 {
512 nsec = nsec + TICK_NSEC - 1;
514 if (sec >= MAX_SEC_IN_JIFFIES){
515 sec = MAX_SEC_IN_JIFFIES;
516 nsec = 0;
517 }
518 return (((u64)sec * SEC_CONVERSION) +
519 (((u64)nsec * NSEC_CONVERSION) >>
520 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
522 }
524 unsigned long
525 timespec_to_jiffies(const struct timespec *value)
526 {
527 return __timespec_to_jiffies(value->tv_sec, value->tv_nsec);
528 }
530 EXPORT_SYMBOL(timespec_to_jiffies);
532 void
533 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
534 {
535 /*
536 * Convert jiffies to nanoseconds and separate with
537 * one divide.
538 */
539 u32 rem;
540 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
541 NSEC_PER_SEC, &rem);
542 value->tv_nsec = rem;
543 }
544 EXPORT_SYMBOL(jiffies_to_timespec);
546 /*
547 * We could use a similar algorithm to timespec_to_jiffies (with a
548 * different multiplier for usec instead of nsec). But this has a
549 * problem with rounding: we can't exactly add TICK_NSEC - 1 to the
550 * usec value, since it's not necessarily integral.
551 *
552 * We could instead round in the intermediate scaled representation
553 * (i.e. in units of 1/2^(large scale) jiffies) but that's also
554 * perilous: the scaling introduces a small positive error, which
555 * combined with a division-rounding-upward (i.e. adding 2^(scale) - 1
556 * units to the intermediate before shifting) leads to accidental
557 * overflow and overestimates.
558 *
559 * At the cost of one additional multiplication by a constant, just
560 * use the timespec implementation.
561 */
562 unsigned long
563 timeval_to_jiffies(const struct timeval *value)
564 {
565 return __timespec_to_jiffies(value->tv_sec,
566 value->tv_usec * NSEC_PER_USEC);
567 }
568 EXPORT_SYMBOL(timeval_to_jiffies);
570 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
571 {
572 /*
573 * Convert jiffies to nanoseconds and separate with
574 * one divide.
575 */
576 u32 rem;
578 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
579 NSEC_PER_SEC, &rem);
580 value->tv_usec = rem / NSEC_PER_USEC;
581 }
582 EXPORT_SYMBOL(jiffies_to_timeval);
584 /*
585 * Convert jiffies/jiffies_64 to clock_t and back.
586 */
587 clock_t jiffies_to_clock_t(unsigned long x)
588 {
589 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
590 # if HZ < USER_HZ
591 return x * (USER_HZ / HZ);
592 # else
593 return x / (HZ / USER_HZ);
594 # endif
595 #else
596 return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
597 #endif
598 }
599 EXPORT_SYMBOL(jiffies_to_clock_t);
601 unsigned long clock_t_to_jiffies(unsigned long x)
602 {
603 #if (HZ % USER_HZ)==0
604 if (x >= ~0UL / (HZ / USER_HZ))
605 return ~0UL;
606 return x * (HZ / USER_HZ);
607 #else
608 /* Don't worry about loss of precision here .. */
609 if (x >= ~0UL / HZ * USER_HZ)
610 return ~0UL;
612 /* .. but do try to contain it here */
613 return div_u64((u64)x * HZ, USER_HZ);
614 #endif
615 }
616 EXPORT_SYMBOL(clock_t_to_jiffies);
618 u64 jiffies_64_to_clock_t(u64 x)
619 {
620 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
621 # if HZ < USER_HZ
622 x = div_u64(x * USER_HZ, HZ);
623 # elif HZ > USER_HZ
624 x = div_u64(x, HZ / USER_HZ);
625 # else
626 /* Nothing to do */
627 # endif
628 #else
629 /*
630 * There are better ways that don't overflow early,
631 * but even this doesn't overflow in hundreds of years
632 * in 64 bits, so..
633 */
634 x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
635 #endif
636 return x;
637 }
638 EXPORT_SYMBOL(jiffies_64_to_clock_t);
640 u64 nsec_to_clock_t(u64 x)
641 {
642 #if (NSEC_PER_SEC % USER_HZ) == 0
643 return div_u64(x, NSEC_PER_SEC / USER_HZ);
644 #elif (USER_HZ % 512) == 0
645 return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
646 #else
647 /*
648 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
649 * overflow after 64.99 years.
650 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
651 */
652 return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
653 #endif
654 }
656 /**
657 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
658 *
659 * @n: nsecs in u64
660 *
661 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
662 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
663 * for scheduler, not for use in device drivers to calculate timeout value.
664 *
665 * note:
666 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
667 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
668 */
669 u64 nsecs_to_jiffies64(u64 n)
670 {
671 #if (NSEC_PER_SEC % HZ) == 0
672 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
673 return div_u64(n, NSEC_PER_SEC / HZ);
674 #elif (HZ % 512) == 0
675 /* overflow after 292 years if HZ = 1024 */
676 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
677 #else
678 /*
679 * Generic case - optimized for cases where HZ is a multiple of 3.
680 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
681 */
682 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
683 #endif
684 }
686 /**
687 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
688 *
689 * @n: nsecs in u64
690 *
691 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
692 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
693 * for scheduler, not for use in device drivers to calculate timeout value.
694 *
695 * note:
696 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
697 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
698 */
699 unsigned long nsecs_to_jiffies(u64 n)
700 {
701 return (unsigned long)nsecs_to_jiffies64(n);
702 }
704 /*
705 * Add two timespec values and do a safety check for overflow.
706 * It's assumed that both values are valid (>= 0)
707 */
708 struct timespec timespec_add_safe(const struct timespec lhs,
709 const struct timespec rhs)
710 {
711 struct timespec res;
713 set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
714 lhs.tv_nsec + rhs.tv_nsec);
716 if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
717 res.tv_sec = TIME_T_MAX;
719 return res;
720 }