4 * Copyright (C) 1991, 1992 Linus Torvalds
6 * This file contains the interface functions for the various
7 * time related system calls: time, stime, gettimeofday, settimeofday,
11 * Modification history kernel/time.c
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
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>
38 #include <linux/math64.h>
39 #include <linux/ptrace.h>
41 #include <asm/uaccess.h>
42 #include <asm/unistd.h>
44 #include "timeconst.h"
45 #include "timekeeping.h"
48 * The timezone where the local system is located. Used as a default by some
49 * programs who obtain this value by using gettimeofday.
51 struct timezone sys_tz;
53 EXPORT_SYMBOL(sys_tz);
55 #ifdef __ARCH_WANT_SYS_TIME
58 * sys_time() can be implemented in user-level using
59 * sys_gettimeofday(). Is this for backwards compatibility? If so,
60 * why not move it into the appropriate arch directory (for those
61 * architectures that need it).
63 SYSCALL_DEFINE1(time, time_t __user *, tloc)
65 time_t i = get_seconds();
71 force_successful_syscall_return();
76 * sys_stime() can be implemented in user-level using
77 * sys_settimeofday(). Is this for backwards compatibility? If so,
78 * why not move it into the appropriate arch directory (for those
79 * architectures that need it).
82 SYSCALL_DEFINE1(stime, time_t __user *, tptr)
87 if (get_user(tv.tv_sec, tptr))
92 err = security_settime(&tv, NULL);
100 #endif /* __ARCH_WANT_SYS_TIME */
102 SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
103 struct timezone __user *, tz)
105 if (likely(tv != NULL)) {
107 do_gettimeofday(&ktv);
108 if (copy_to_user(tv, &ktv, sizeof(ktv)))
111 if (unlikely(tz != NULL)) {
112 if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
119 * Indicates if there is an offset between the system clock and the hardware
120 * clock/persistent clock/rtc.
122 int persistent_clock_is_local;
125 * Adjust the time obtained from the CMOS to be UTC time instead of
128 * This is ugly, but preferable to the alternatives. Otherwise we
129 * would either need to write a program to do it in /etc/rc (and risk
130 * confusion if the program gets run more than once; it would also be
131 * hard to make the program warp the clock precisely n hours) or
132 * compile in the timezone information into the kernel. Bad, bad....
136 * The best thing to do is to keep the CMOS clock in universal time (UTC)
137 * as real UNIX machines always do it. This avoids all headaches about
138 * daylight saving times and warping kernel clocks.
140 static inline void warp_clock(void)
142 if (sys_tz.tz_minuteswest != 0) {
143 struct timespec adjust;
145 persistent_clock_is_local = 1;
146 adjust.tv_sec = sys_tz.tz_minuteswest * 60;
148 timekeeping_inject_offset(&adjust);
153 * In case for some reason the CMOS clock has not already been running
154 * in UTC, but in some local time: The first time we set the timezone,
155 * we will warp the clock so that it is ticking UTC time instead of
156 * local time. Presumably, if someone is setting the timezone then we
157 * are running in an environment where the programs understand about
158 * timezones. This should be done at boot time in the /etc/rc script,
159 * as soon as possible, so that the clock can be set right. Otherwise,
160 * various programs will get confused when the clock gets warped.
163 int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
165 static int firsttime = 1;
168 if (tv && !timespec_valid(tv))
171 error = security_settime(tv, tz);
177 update_vsyscall_tz();
185 return do_settimeofday(tv);
189 SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
190 struct timezone __user *, tz)
192 struct timeval user_tv;
193 struct timespec new_ts;
194 struct timezone new_tz;
197 if (copy_from_user(&user_tv, tv, sizeof(*tv)))
199 new_ts.tv_sec = user_tv.tv_sec;
200 new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
203 if (copy_from_user(&new_tz, tz, sizeof(*tz)))
207 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
210 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
212 struct timex txc; /* Local copy of parameter */
215 /* Copy the user data space into the kernel copy
216 * structure. But bear in mind that the structures
219 if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
221 ret = do_adjtimex(&txc);
222 return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
226 * current_fs_time - Return FS time
229 * Return the current time truncated to the time granularity supported by
232 struct timespec current_fs_time(struct super_block *sb)
234 struct timespec now = current_kernel_time();
235 return timespec_trunc(now, sb->s_time_gran);
237 EXPORT_SYMBOL(current_fs_time);
240 * Convert jiffies to milliseconds and back.
242 * Avoid unnecessary multiplications/divisions in the
243 * two most common HZ cases:
245 unsigned int jiffies_to_msecs(const unsigned long j)
247 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
248 return (MSEC_PER_SEC / HZ) * j;
249 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
250 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
252 # if BITS_PER_LONG == 32
253 return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
255 return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
259 EXPORT_SYMBOL(jiffies_to_msecs);
261 unsigned int jiffies_to_usecs(const unsigned long j)
263 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
264 return (USEC_PER_SEC / HZ) * j;
265 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
266 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
268 # if BITS_PER_LONG == 32
269 return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
271 return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
275 EXPORT_SYMBOL(jiffies_to_usecs);
278 * timespec_trunc - Truncate timespec to a granularity
280 * @gran: Granularity in ns.
282 * Truncate a timespec to a granularity. gran must be smaller than a second.
283 * Always rounds down.
285 * This function should be only used for timestamps returned by
286 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
287 * it doesn't handle the better resolution of the latter.
289 struct timespec timespec_trunc(struct timespec t, unsigned gran)
292 * Division is pretty slow so avoid it for common cases.
293 * Currently current_kernel_time() never returns better than
294 * jiffies resolution. Exploit that.
296 if (gran <= jiffies_to_usecs(1) * 1000) {
298 } else if (gran == 1000000000) {
301 t.tv_nsec -= t.tv_nsec % gran;
305 EXPORT_SYMBOL(timespec_trunc);
307 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
308 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
309 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
311 * [For the Julian calendar (which was used in Russia before 1917,
312 * Britain & colonies before 1752, anywhere else before 1582,
313 * and is still in use by some communities) leave out the
314 * -year/100+year/400 terms, and add 10.]
316 * This algorithm was first published by Gauss (I think).
318 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
319 * machines where long is 32-bit! (However, as time_t is signed, we
320 * will already get problems at other places on 2038-01-19 03:14:08)
323 mktime(const unsigned int year0, const unsigned int mon0,
324 const unsigned int day, const unsigned int hour,
325 const unsigned int min, const unsigned int sec)
327 unsigned int mon = mon0, year = year0;
329 /* 1..12 -> 11,12,1..10 */
330 if (0 >= (int) (mon -= 2)) {
331 mon += 12; /* Puts Feb last since it has leap day */
335 return ((((unsigned long)
336 (year/4 - year/100 + year/400 + 367*mon/12 + day) +
338 )*24 + hour /* now have hours */
339 )*60 + min /* now have minutes */
340 )*60 + sec; /* finally seconds */
343 EXPORT_SYMBOL(mktime);
346 * set_normalized_timespec - set timespec sec and nsec parts and normalize
348 * @ts: pointer to timespec variable to be set
349 * @sec: seconds to set
350 * @nsec: nanoseconds to set
352 * Set seconds and nanoseconds field of a timespec variable and
353 * normalize to the timespec storage format
355 * Note: The tv_nsec part is always in the range of
356 * 0 <= tv_nsec < NSEC_PER_SEC
357 * For negative values only the tv_sec field is negative !
359 void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
361 while (nsec >= NSEC_PER_SEC) {
363 * The following asm() prevents the compiler from
364 * optimising this loop into a modulo operation. See
365 * also __iter_div_u64_rem() in include/linux/time.h
367 asm("" : "+rm"(nsec));
368 nsec -= NSEC_PER_SEC;
372 asm("" : "+rm"(nsec));
373 nsec += NSEC_PER_SEC;
379 EXPORT_SYMBOL(set_normalized_timespec);
382 * ns_to_timespec - Convert nanoseconds to timespec
383 * @nsec: the nanoseconds value to be converted
385 * Returns the timespec representation of the nsec parameter.
387 struct timespec ns_to_timespec(const s64 nsec)
393 return (struct timespec) {0, 0};
395 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
396 if (unlikely(rem < 0)) {
404 EXPORT_SYMBOL(ns_to_timespec);
407 * ns_to_timeval - Convert nanoseconds to timeval
408 * @nsec: the nanoseconds value to be converted
410 * Returns the timeval representation of the nsec parameter.
412 struct timeval ns_to_timeval(const s64 nsec)
414 struct timespec ts = ns_to_timespec(nsec);
417 tv.tv_sec = ts.tv_sec;
418 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
422 EXPORT_SYMBOL(ns_to_timeval);
424 #if BITS_PER_LONG == 32
426 * set_normalized_timespec - set timespec sec and nsec parts and normalize
428 * @ts: pointer to timespec variable to be set
429 * @sec: seconds to set
430 * @nsec: nanoseconds to set
432 * Set seconds and nanoseconds field of a timespec variable and
433 * normalize to the timespec storage format
435 * Note: The tv_nsec part is always in the range of
436 * 0 <= tv_nsec < NSEC_PER_SEC
437 * For negative values only the tv_sec field is negative !
439 void set_normalized_timespec64(struct timespec64 *ts, time64_t sec, s64 nsec)
441 while (nsec >= NSEC_PER_SEC) {
443 * The following asm() prevents the compiler from
444 * optimising this loop into a modulo operation. See
445 * also __iter_div_u64_rem() in include/linux/time.h
447 asm("" : "+rm"(nsec));
448 nsec -= NSEC_PER_SEC;
452 asm("" : "+rm"(nsec));
453 nsec += NSEC_PER_SEC;
459 EXPORT_SYMBOL(set_normalized_timespec64);
462 * ns_to_timespec64 - Convert nanoseconds to timespec64
463 * @nsec: the nanoseconds value to be converted
465 * Returns the timespec64 representation of the nsec parameter.
467 struct timespec64 ns_to_timespec64(const s64 nsec)
469 struct timespec64 ts;
473 return (struct timespec64) {0, 0};
475 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
476 if (unlikely(rem < 0)) {
484 EXPORT_SYMBOL(ns_to_timespec64);
487 * When we convert to jiffies then we interpret incoming values
490 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
492 * - 'too large' values [that would result in larger than
493 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
495 * - all other values are converted to jiffies by either multiplying
496 * the input value by a factor or dividing it with a factor
498 * We must also be careful about 32-bit overflows.
500 unsigned long msecs_to_jiffies(const unsigned int m)
503 * Negative value, means infinite timeout:
506 return MAX_JIFFY_OFFSET;
508 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
510 * HZ is equal to or smaller than 1000, and 1000 is a nice
511 * round multiple of HZ, divide with the factor between them,
514 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
515 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
517 * HZ is larger than 1000, and HZ is a nice round multiple of
518 * 1000 - simply multiply with the factor between them.
520 * But first make sure the multiplication result cannot
523 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
524 return MAX_JIFFY_OFFSET;
526 return m * (HZ / MSEC_PER_SEC);
529 * Generic case - multiply, round and divide. But first
530 * check that if we are doing a net multiplication, that
531 * we wouldn't overflow:
533 if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
534 return MAX_JIFFY_OFFSET;
536 return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
540 EXPORT_SYMBOL(msecs_to_jiffies);
542 unsigned long usecs_to_jiffies(const unsigned int u)
544 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
545 return MAX_JIFFY_OFFSET;
546 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
547 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
548 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
549 return u * (HZ / USEC_PER_SEC);
551 return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
555 EXPORT_SYMBOL(usecs_to_jiffies);
558 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
559 * that a remainder subtract here would not do the right thing as the
560 * resolution values don't fall on second boundries. I.e. the line:
561 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
562 * Note that due to the small error in the multiplier here, this
563 * rounding is incorrect for sufficiently large values of tv_nsec, but
564 * well formed timespecs should have tv_nsec < NSEC_PER_SEC, so we're
567 * Rather, we just shift the bits off the right.
569 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
570 * value to a scaled second value.
573 __timespec_to_jiffies(unsigned long sec, long nsec)
575 nsec = nsec + TICK_NSEC - 1;
577 if (sec >= MAX_SEC_IN_JIFFIES){
578 sec = MAX_SEC_IN_JIFFIES;
581 return (((u64)sec * SEC_CONVERSION) +
582 (((u64)nsec * NSEC_CONVERSION) >>
583 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
588 timespec_to_jiffies(const struct timespec *value)
590 return __timespec_to_jiffies(value->tv_sec, value->tv_nsec);
593 EXPORT_SYMBOL(timespec_to_jiffies);
596 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
599 * Convert jiffies to nanoseconds and separate with
603 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
605 value->tv_nsec = rem;
607 EXPORT_SYMBOL(jiffies_to_timespec);
610 * We could use a similar algorithm to timespec_to_jiffies (with a
611 * different multiplier for usec instead of nsec). But this has a
612 * problem with rounding: we can't exactly add TICK_NSEC - 1 to the
613 * usec value, since it's not necessarily integral.
615 * We could instead round in the intermediate scaled representation
616 * (i.e. in units of 1/2^(large scale) jiffies) but that's also
617 * perilous: the scaling introduces a small positive error, which
618 * combined with a division-rounding-upward (i.e. adding 2^(scale) - 1
619 * units to the intermediate before shifting) leads to accidental
620 * overflow and overestimates.
622 * At the cost of one additional multiplication by a constant, just
623 * use the timespec implementation.
626 timeval_to_jiffies(const struct timeval *value)
628 return __timespec_to_jiffies(value->tv_sec,
629 value->tv_usec * NSEC_PER_USEC);
631 EXPORT_SYMBOL(timeval_to_jiffies);
633 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
636 * Convert jiffies to nanoseconds and separate with
641 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
643 value->tv_usec = rem / NSEC_PER_USEC;
645 EXPORT_SYMBOL(jiffies_to_timeval);
648 * Convert jiffies/jiffies_64 to clock_t and back.
650 clock_t jiffies_to_clock_t(unsigned long x)
652 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
654 return x * (USER_HZ / HZ);
656 return x / (HZ / USER_HZ);
659 return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
662 EXPORT_SYMBOL(jiffies_to_clock_t);
664 unsigned long clock_t_to_jiffies(unsigned long x)
666 #if (HZ % USER_HZ)==0
667 if (x >= ~0UL / (HZ / USER_HZ))
669 return x * (HZ / USER_HZ);
671 /* Don't worry about loss of precision here .. */
672 if (x >= ~0UL / HZ * USER_HZ)
675 /* .. but do try to contain it here */
676 return div_u64((u64)x * HZ, USER_HZ);
679 EXPORT_SYMBOL(clock_t_to_jiffies);
681 u64 jiffies_64_to_clock_t(u64 x)
683 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
685 x = div_u64(x * USER_HZ, HZ);
687 x = div_u64(x, HZ / USER_HZ);
693 * There are better ways that don't overflow early,
694 * but even this doesn't overflow in hundreds of years
697 x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
701 EXPORT_SYMBOL(jiffies_64_to_clock_t);
703 u64 nsec_to_clock_t(u64 x)
705 #if (NSEC_PER_SEC % USER_HZ) == 0
706 return div_u64(x, NSEC_PER_SEC / USER_HZ);
707 #elif (USER_HZ % 512) == 0
708 return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
711 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
712 * overflow after 64.99 years.
713 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
715 return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
720 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
724 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
725 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
726 * for scheduler, not for use in device drivers to calculate timeout value.
729 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
730 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
732 u64 nsecs_to_jiffies64(u64 n)
734 #if (NSEC_PER_SEC % HZ) == 0
735 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
736 return div_u64(n, NSEC_PER_SEC / HZ);
737 #elif (HZ % 512) == 0
738 /* overflow after 292 years if HZ = 1024 */
739 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
742 * Generic case - optimized for cases where HZ is a multiple of 3.
743 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
745 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
750 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
754 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
755 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
756 * for scheduler, not for use in device drivers to calculate timeout value.
759 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
760 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
762 unsigned long nsecs_to_jiffies(u64 n)
764 return (unsigned long)nsecs_to_jiffies64(n);
766 EXPORT_SYMBOL_GPL(nsecs_to_jiffies);
769 * Add two timespec values and do a safety check for overflow.
770 * It's assumed that both values are valid (>= 0)
772 struct timespec timespec_add_safe(const struct timespec lhs,
773 const struct timespec rhs)
777 set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
778 lhs.tv_nsec + rhs.tv_nsec);
780 if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
781 res.tv_sec = TIME_T_MAX;