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.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"
47 * The timezone where the local system is located. Used as a default by some
48 * programs who obtain this value by using gettimeofday.
50 struct timezone sys_tz;
52 EXPORT_SYMBOL(sys_tz);
54 #ifdef __ARCH_WANT_SYS_TIME
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).
62 SYSCALL_DEFINE1(time, time_t __user *, tloc)
64 time_t i = get_seconds();
70 force_successful_syscall_return();
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).
81 SYSCALL_DEFINE1(stime, time_t __user *, tptr)
86 if (get_user(tv.tv_sec, tptr))
91 err = security_settime(&tv, NULL);
99 #endif /* __ARCH_WANT_SYS_TIME */
101 SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
102 struct timezone __user *, tz)
104 if (likely(tv != NULL)) {
106 do_gettimeofday(&ktv);
107 if (copy_to_user(tv, &ktv, sizeof(ktv)))
110 if (unlikely(tz != NULL)) {
111 if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
118 * Indicates if there is an offset between the system clock and the hardware
119 * clock/persistent clock/rtc.
121 int persistent_clock_is_local;
124 * Adjust the time obtained from the CMOS to be UTC time instead of
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....
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.
139 static inline void warp_clock(void)
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;
147 timekeeping_inject_offset(&adjust);
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.
162 int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
164 static int firsttime = 1;
167 if (tv && !timespec_valid(tv))
170 error = security_settime(tv, tz);
176 update_vsyscall_tz();
184 return do_settimeofday(tv);
188 SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
189 struct timezone __user *, tz)
191 struct timeval user_tv;
192 struct timespec new_ts;
193 struct timezone new_tz;
196 if (copy_from_user(&user_tv, tv, sizeof(*tv)))
199 if (!timeval_valid(&user_tv))
202 new_ts.tv_sec = user_tv.tv_sec;
203 new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
206 if (copy_from_user(&new_tz, tz, sizeof(*tz)))
210 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
213 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
215 struct timex txc; /* Local copy of parameter */
218 /* Copy the user data space into the kernel copy
219 * structure. But bear in mind that the structures
222 if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
224 ret = do_adjtimex(&txc);
225 return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
229 * current_fs_time - Return FS time
232 * Return the current time truncated to the time granularity supported by
235 struct timespec current_fs_time(struct super_block *sb)
237 struct timespec now = current_kernel_time();
238 return timespec_trunc(now, sb->s_time_gran);
240 EXPORT_SYMBOL(current_fs_time);
243 * Convert jiffies to milliseconds and back.
245 * Avoid unnecessary multiplications/divisions in the
246 * two most common HZ cases:
248 unsigned int jiffies_to_msecs(const unsigned long j)
250 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
251 return (MSEC_PER_SEC / HZ) * j;
252 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
253 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
255 # if BITS_PER_LONG == 32
256 return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
258 return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
262 EXPORT_SYMBOL(jiffies_to_msecs);
264 unsigned int jiffies_to_usecs(const unsigned long j)
266 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
267 return (USEC_PER_SEC / HZ) * j;
268 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
269 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
271 # if BITS_PER_LONG == 32
272 return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
274 return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
278 EXPORT_SYMBOL(jiffies_to_usecs);
281 * timespec_trunc - Truncate timespec to a granularity
283 * @gran: Granularity in ns.
285 * Truncate a timespec to a granularity. gran must be smaller than a second.
286 * Always rounds down.
288 * This function should be only used for timestamps returned by
289 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
290 * it doesn't handle the better resolution of the latter.
292 struct timespec timespec_trunc(struct timespec t, unsigned gran)
295 * Division is pretty slow so avoid it for common cases.
296 * Currently current_kernel_time() never returns better than
297 * jiffies resolution. Exploit that.
299 if (gran <= jiffies_to_usecs(1) * 1000) {
301 } else if (gran == 1000000000) {
304 t.tv_nsec -= t.tv_nsec % gran;
308 EXPORT_SYMBOL(timespec_trunc);
310 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
311 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
312 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
314 * [For the Julian calendar (which was used in Russia before 1917,
315 * Britain & colonies before 1752, anywhere else before 1582,
316 * and is still in use by some communities) leave out the
317 * -year/100+year/400 terms, and add 10.]
319 * This algorithm was first published by Gauss (I think).
321 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
322 * machines where long is 32-bit! (However, as time_t is signed, we
323 * will already get problems at other places on 2038-01-19 03:14:08)
326 mktime(const unsigned int year0, const unsigned int mon0,
327 const unsigned int day, const unsigned int hour,
328 const unsigned int min, const unsigned int sec)
330 unsigned int mon = mon0, year = year0;
332 /* 1..12 -> 11,12,1..10 */
333 if (0 >= (int) (mon -= 2)) {
334 mon += 12; /* Puts Feb last since it has leap day */
338 return ((((unsigned long)
339 (year/4 - year/100 + year/400 + 367*mon/12 + day) +
341 )*24 + hour /* now have hours */
342 )*60 + min /* now have minutes */
343 )*60 + sec; /* finally seconds */
346 EXPORT_SYMBOL(mktime);
349 * set_normalized_timespec - set timespec sec and nsec parts and normalize
351 * @ts: pointer to timespec variable to be set
352 * @sec: seconds to set
353 * @nsec: nanoseconds to set
355 * Set seconds and nanoseconds field of a timespec variable and
356 * normalize to the timespec storage format
358 * Note: The tv_nsec part is always in the range of
359 * 0 <= tv_nsec < NSEC_PER_SEC
360 * For negative values only the tv_sec field is negative !
362 void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
364 while (nsec >= NSEC_PER_SEC) {
366 * The following asm() prevents the compiler from
367 * optimising this loop into a modulo operation. See
368 * also __iter_div_u64_rem() in include/linux/time.h
370 asm("" : "+rm"(nsec));
371 nsec -= NSEC_PER_SEC;
375 asm("" : "+rm"(nsec));
376 nsec += NSEC_PER_SEC;
382 EXPORT_SYMBOL(set_normalized_timespec);
385 * ns_to_timespec - Convert nanoseconds to timespec
386 * @nsec: the nanoseconds value to be converted
388 * Returns the timespec representation of the nsec parameter.
390 struct timespec ns_to_timespec(const s64 nsec)
396 return (struct timespec) {0, 0};
398 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
399 if (unlikely(rem < 0)) {
407 EXPORT_SYMBOL(ns_to_timespec);
410 * ns_to_timeval - Convert nanoseconds to timeval
411 * @nsec: the nanoseconds value to be converted
413 * Returns the timeval representation of the nsec parameter.
415 struct timeval ns_to_timeval(const s64 nsec)
417 struct timespec ts = ns_to_timespec(nsec);
420 tv.tv_sec = ts.tv_sec;
421 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
425 EXPORT_SYMBOL(ns_to_timeval);
428 * When we convert to jiffies then we interpret incoming values
431 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
433 * - 'too large' values [that would result in larger than
434 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
436 * - all other values are converted to jiffies by either multiplying
437 * the input value by a factor or dividing it with a factor
439 * We must also be careful about 32-bit overflows.
441 unsigned long msecs_to_jiffies(const unsigned int m)
444 * Negative value, means infinite timeout:
447 return MAX_JIFFY_OFFSET;
449 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
451 * HZ is equal to or smaller than 1000, and 1000 is a nice
452 * round multiple of HZ, divide with the factor between them,
455 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
456 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
458 * HZ is larger than 1000, and HZ is a nice round multiple of
459 * 1000 - simply multiply with the factor between them.
461 * But first make sure the multiplication result cannot
464 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
465 return MAX_JIFFY_OFFSET;
467 return m * (HZ / MSEC_PER_SEC);
470 * Generic case - multiply, round and divide. But first
471 * check that if we are doing a net multiplication, that
472 * we wouldn't overflow:
474 if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
475 return MAX_JIFFY_OFFSET;
477 return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
481 EXPORT_SYMBOL(msecs_to_jiffies);
483 unsigned long usecs_to_jiffies(const unsigned int u)
485 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
486 return MAX_JIFFY_OFFSET;
487 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
488 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
489 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
490 return u * (HZ / USEC_PER_SEC);
492 return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
496 EXPORT_SYMBOL(usecs_to_jiffies);
499 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
500 * that a remainder subtract here would not do the right thing as the
501 * resolution values don't fall on second boundries. I.e. the line:
502 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
503 * Note that due to the small error in the multiplier here, this
504 * rounding is incorrect for sufficiently large values of tv_nsec, but
505 * well formed timespecs should have tv_nsec < NSEC_PER_SEC, so we're
508 * Rather, we just shift the bits off the right.
510 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
511 * value to a scaled second value.
514 __timespec_to_jiffies(unsigned long sec, long nsec)
516 nsec = nsec + TICK_NSEC - 1;
518 if (sec >= MAX_SEC_IN_JIFFIES){
519 sec = MAX_SEC_IN_JIFFIES;
522 return (((u64)sec * SEC_CONVERSION) +
523 (((u64)nsec * NSEC_CONVERSION) >>
524 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
529 timespec_to_jiffies(const struct timespec *value)
531 return __timespec_to_jiffies(value->tv_sec, value->tv_nsec);
534 EXPORT_SYMBOL(timespec_to_jiffies);
537 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
540 * Convert jiffies to nanoseconds and separate with
544 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
546 value->tv_nsec = rem;
548 EXPORT_SYMBOL(jiffies_to_timespec);
551 * We could use a similar algorithm to timespec_to_jiffies (with a
552 * different multiplier for usec instead of nsec). But this has a
553 * problem with rounding: we can't exactly add TICK_NSEC - 1 to the
554 * usec value, since it's not necessarily integral.
556 * We could instead round in the intermediate scaled representation
557 * (i.e. in units of 1/2^(large scale) jiffies) but that's also
558 * perilous: the scaling introduces a small positive error, which
559 * combined with a division-rounding-upward (i.e. adding 2^(scale) - 1
560 * units to the intermediate before shifting) leads to accidental
561 * overflow and overestimates.
563 * At the cost of one additional multiplication by a constant, just
564 * use the timespec implementation.
567 timeval_to_jiffies(const struct timeval *value)
569 return __timespec_to_jiffies(value->tv_sec,
570 value->tv_usec * NSEC_PER_USEC);
572 EXPORT_SYMBOL(timeval_to_jiffies);
574 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
577 * Convert jiffies to nanoseconds and separate with
582 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
584 value->tv_usec = rem / NSEC_PER_USEC;
586 EXPORT_SYMBOL(jiffies_to_timeval);
589 * Convert jiffies/jiffies_64 to clock_t and back.
591 clock_t jiffies_to_clock_t(unsigned long x)
593 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
595 return x * (USER_HZ / HZ);
597 return x / (HZ / USER_HZ);
600 return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
603 EXPORT_SYMBOL(jiffies_to_clock_t);
605 unsigned long clock_t_to_jiffies(unsigned long x)
607 #if (HZ % USER_HZ)==0
608 if (x >= ~0UL / (HZ / USER_HZ))
610 return x * (HZ / USER_HZ);
612 /* Don't worry about loss of precision here .. */
613 if (x >= ~0UL / HZ * USER_HZ)
616 /* .. but do try to contain it here */
617 return div_u64((u64)x * HZ, USER_HZ);
620 EXPORT_SYMBOL(clock_t_to_jiffies);
622 u64 jiffies_64_to_clock_t(u64 x)
624 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
626 x = div_u64(x * USER_HZ, HZ);
628 x = div_u64(x, HZ / USER_HZ);
634 * There are better ways that don't overflow early,
635 * but even this doesn't overflow in hundreds of years
638 x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
642 EXPORT_SYMBOL(jiffies_64_to_clock_t);
644 u64 nsec_to_clock_t(u64 x)
646 #if (NSEC_PER_SEC % USER_HZ) == 0
647 return div_u64(x, NSEC_PER_SEC / USER_HZ);
648 #elif (USER_HZ % 512) == 0
649 return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
652 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
653 * overflow after 64.99 years.
654 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
656 return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
661 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
665 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
666 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
667 * for scheduler, not for use in device drivers to calculate timeout value.
670 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
671 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
673 u64 nsecs_to_jiffies64(u64 n)
675 #if (NSEC_PER_SEC % HZ) == 0
676 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
677 return div_u64(n, NSEC_PER_SEC / HZ);
678 #elif (HZ % 512) == 0
679 /* overflow after 292 years if HZ = 1024 */
680 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
683 * Generic case - optimized for cases where HZ is a multiple of 3.
684 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
686 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
691 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
695 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
696 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
697 * for scheduler, not for use in device drivers to calculate timeout value.
700 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
701 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
703 unsigned long nsecs_to_jiffies(u64 n)
705 return (unsigned long)nsecs_to_jiffies64(n);
709 * Add two timespec values and do a safety check for overflow.
710 * It's assumed that both values are valid (>= 0)
712 struct timespec timespec_add_safe(const struct timespec lhs,
713 const struct timespec rhs)
717 set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
718 lhs.tv_nsec + rhs.tv_nsec);
720 if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
721 res.tv_sec = TIME_T_MAX;