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time.c
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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>
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  */
51 
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  */
62 SYSCALL_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  }
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 
81 SYSCALL_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 
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 }
116 
117 /*
118  * Adjust the time obtained from the CMOS to be UTC time instead of
119  * local time.
120  *
121  * This is ugly, but preferable to the alternatives. Otherwise we
122  * would either need to write a program to do it in /etc/rc (and risk
123  * confusion if the program gets run more than once; it would also be
124  * hard to make the program warp the clock precisely n hours) or
125  * compile in the timezone information into the kernel. Bad, bad....
126  *
127  * - TYT, 1992-01-01
128  *
129  * The best thing to do is to keep the CMOS clock in universal time (UTC)
130  * as real UNIX machines always do it. This avoids all headaches about
131  * daylight saving times and warping kernel clocks.
132  */
133 static inline void warp_clock(void)
134 {
135  struct timespec adjust;
136 
138  adjust.tv_sec += sys_tz.tz_minuteswest * 60;
139  do_settimeofday(&adjust);
140 }
141 
142 /*
143  * In case for some reason the CMOS clock has not already been running
144  * in UTC, but in some local time: The first time we set the timezone,
145  * we will warp the clock so that it is ticking UTC time instead of
146  * local time. Presumably, if someone is setting the timezone then we
147  * are running in an environment where the programs understand about
148  * timezones. This should be done at boot time in the /etc/rc script,
149  * as soon as possible, so that the clock can be set right. Otherwise,
150  * various programs will get confused when the clock gets warped.
151  */
152 
153 int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
154 {
155  static int firsttime = 1;
156  int error = 0;
157 
158  if (tv && !timespec_valid(tv))
159  return -EINVAL;
160 
161  error = security_settime(tv, tz);
162  if (error)
163  return error;
164 
165  if (tz) {
166  sys_tz = *tz;
168  if (firsttime) {
169  firsttime = 0;
170  if (!tv)
171  warp_clock();
172  }
173  }
174  if (tv)
175  return do_settimeofday(tv);
176  return 0;
177 }
178 
179 SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
180  struct timezone __user *, tz)
181 {
182  struct timeval user_tv;
183  struct timespec new_ts;
184  struct timezone new_tz;
185 
186  if (tv) {
187  if (copy_from_user(&user_tv, tv, sizeof(*tv)))
188  return -EFAULT;
189  new_ts.tv_sec = user_tv.tv_sec;
190  new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
191  }
192  if (tz) {
193  if (copy_from_user(&new_tz, tz, sizeof(*tz)))
194  return -EFAULT;
195  }
196 
197  return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
198 }
199 
200 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
201 {
202  struct timex txc; /* Local copy of parameter */
203  int ret;
204 
205  /* Copy the user data space into the kernel copy
206  * structure. But bear in mind that the structures
207  * may change
208  */
209  if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
210  return -EFAULT;
211  ret = do_adjtimex(&txc);
212  return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
213 }
214 
223 {
224  struct timespec now = current_kernel_time();
225  return timespec_trunc(now, sb->s_time_gran);
226 }
228 
229 /*
230  * Convert jiffies to milliseconds and back.
231  *
232  * Avoid unnecessary multiplications/divisions in the
233  * two most common HZ cases:
234  */
235 inline unsigned int jiffies_to_msecs(const unsigned long j)
236 {
237 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
238  return (MSEC_PER_SEC / HZ) * j;
239 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
240  return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
241 #else
242 # if BITS_PER_LONG == 32
243  return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
244 # else
245  return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
246 # endif
247 #endif
248 }
250 
251 inline unsigned int jiffies_to_usecs(const unsigned long j)
252 {
253 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
254  return (USEC_PER_SEC / HZ) * j;
255 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
256  return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
257 #else
258 # if BITS_PER_LONG == 32
259  return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
260 # else
261  return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
262 # endif
263 #endif
264 }
266 
279 struct timespec timespec_trunc(struct timespec t, unsigned gran)
280 {
281  /*
282  * Division is pretty slow so avoid it for common cases.
283  * Currently current_kernel_time() never returns better than
284  * jiffies resolution. Exploit that.
285  */
286  if (gran <= jiffies_to_usecs(1) * 1000) {
287  /* nothing */
288  } else if (gran == 1000000000) {
289  t.tv_nsec = 0;
290  } else {
291  t.tv_nsec -= t.tv_nsec % gran;
292  }
293  return t;
294 }
296 
297 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
298  * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
299  * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
300  *
301  * [For the Julian calendar (which was used in Russia before 1917,
302  * Britain & colonies before 1752, anywhere else before 1582,
303  * and is still in use by some communities) leave out the
304  * -year/100+year/400 terms, and add 10.]
305  *
306  * This algorithm was first published by Gauss (I think).
307  *
308  * WARNING: this function will overflow on 2106-02-07 06:28:16 on
309  * machines where long is 32-bit! (However, as time_t is signed, we
310  * will already get problems at other places on 2038-01-19 03:14:08)
311  */
312 unsigned long
313 mktime(const unsigned int year0, const unsigned int mon0,
314  const unsigned int day, const unsigned int hour,
315  const unsigned int min, const unsigned int sec)
316 {
317  unsigned int mon = mon0, year = year0;
318 
319  /* 1..12 -> 11,12,1..10 */
320  if (0 >= (int) (mon -= 2)) {
321  mon += 12; /* Puts Feb last since it has leap day */
322  year -= 1;
323  }
324 
325  return ((((unsigned long)
326  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
327  year*365 - 719499
328  )*24 + hour /* now have hours */
329  )*60 + min /* now have minutes */
330  )*60 + sec; /* finally seconds */
331 }
332 
334 
350 {
351  while (nsec >= NSEC_PER_SEC) {
352  /*
353  * The following asm() prevents the compiler from
354  * optimising this loop into a modulo operation. See
355  * also __iter_div_u64_rem() in include/linux/time.h
356  */
357  asm("" : "+rm"(nsec));
358  nsec -= NSEC_PER_SEC;
359  ++sec;
360  }
361  while (nsec < 0) {
362  asm("" : "+rm"(nsec));
363  nsec += NSEC_PER_SEC;
364  --sec;
365  }
366  ts->tv_sec = sec;
367  ts->tv_nsec = nsec;
368 }
370 
378 {
379  struct timespec ts;
380  s32 rem;
381 
382  if (!nsec)
383  return (struct timespec) {0, 0};
384 
385  ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
386  if (unlikely(rem < 0)) {
387  ts.tv_sec--;
388  rem += NSEC_PER_SEC;
389  }
390  ts.tv_nsec = rem;
391 
392  return ts;
393 }
395 
403 {
404  struct timespec ts = ns_to_timespec(nsec);
405  struct timeval tv;
406 
407  tv.tv_sec = ts.tv_sec;
408  tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
409 
410  return tv;
411 }
413 
414 /*
415  * When we convert to jiffies then we interpret incoming values
416  * the following way:
417  *
418  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
419  *
420  * - 'too large' values [that would result in larger than
421  * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
422  *
423  * - all other values are converted to jiffies by either multiplying
424  * the input value by a factor or dividing it with a factor
425  *
426  * We must also be careful about 32-bit overflows.
427  */
428 unsigned long msecs_to_jiffies(const unsigned int m)
429 {
430  /*
431  * Negative value, means infinite timeout:
432  */
433  if ((int)m < 0)
434  return MAX_JIFFY_OFFSET;
435 
436 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
437  /*
438  * HZ is equal to or smaller than 1000, and 1000 is a nice
439  * round multiple of HZ, divide with the factor between them,
440  * but round upwards:
441  */
442  return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
443 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
444  /*
445  * HZ is larger than 1000, and HZ is a nice round multiple of
446  * 1000 - simply multiply with the factor between them.
447  *
448  * But first make sure the multiplication result cannot
449  * overflow:
450  */
452  return MAX_JIFFY_OFFSET;
453 
454  return m * (HZ / MSEC_PER_SEC);
455 #else
456  /*
457  * Generic case - multiply, round and divide. But first
458  * check that if we are doing a net multiplication, that
459  * we wouldn't overflow:
460  */
462  return MAX_JIFFY_OFFSET;
463 
464  return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
465  >> MSEC_TO_HZ_SHR32;
466 #endif
467 }
469 
470 unsigned long usecs_to_jiffies(const unsigned int u)
471 {
473  return MAX_JIFFY_OFFSET;
474 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
475  return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
476 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
477  return u * (HZ / USEC_PER_SEC);
478 #else
479  return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
480  >> USEC_TO_HZ_SHR32;
481 #endif
482 }
484 
485 /*
486  * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
487  * that a remainder subtract here would not do the right thing as the
488  * resolution values don't fall on second boundries. I.e. the line:
489  * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
490  *
491  * Rather, we just shift the bits off the right.
492  *
493  * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
494  * value to a scaled second value.
495  */
496 unsigned long
498 {
499  unsigned long sec = value->tv_sec;
500  long nsec = value->tv_nsec + TICK_NSEC - 1;
501 
502  if (sec >= MAX_SEC_IN_JIFFIES){
503  sec = MAX_SEC_IN_JIFFIES;
504  nsec = 0;
505  }
506  return (((u64)sec * SEC_CONVERSION) +
507  (((u64)nsec * NSEC_CONVERSION) >>
509 
510 }
512 
513 void
514 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
515 {
516  /*
517  * Convert jiffies to nanoseconds and separate with
518  * one divide.
519  */
520  u32 rem;
521  value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
522  NSEC_PER_SEC, &rem);
523  value->tv_nsec = rem;
524 }
526 
527 /* Same for "timeval"
528  *
529  * Well, almost. The problem here is that the real system resolution is
530  * in nanoseconds and the value being converted is in micro seconds.
531  * Also for some machines (those that use HZ = 1024, in-particular),
532  * there is a LARGE error in the tick size in microseconds.
533 
534  * The solution we use is to do the rounding AFTER we convert the
535  * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
536  * Instruction wise, this should cost only an additional add with carry
537  * instruction above the way it was done above.
538  */
539 unsigned long
541 {
542  unsigned long sec = value->tv_sec;
543  long usec = value->tv_usec;
544 
545  if (sec >= MAX_SEC_IN_JIFFIES){
546  sec = MAX_SEC_IN_JIFFIES;
547  usec = 0;
548  }
549  return (((u64)sec * SEC_CONVERSION) +
550  (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
552 }
554 
555 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
556 {
557  /*
558  * Convert jiffies to nanoseconds and separate with
559  * one divide.
560  */
561  u32 rem;
562 
563  value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
564  NSEC_PER_SEC, &rem);
565  value->tv_usec = rem / NSEC_PER_USEC;
566 }
568 
569 /*
570  * Convert jiffies/jiffies_64 to clock_t and back.
571  */
573 {
574 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
575 # if HZ < USER_HZ
576  return x * (USER_HZ / HZ);
577 # else
578  return x / (HZ / USER_HZ);
579 # endif
580 #else
581  return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
582 #endif
583 }
585 
586 unsigned long clock_t_to_jiffies(unsigned long x)
587 {
588 #if (HZ % USER_HZ)==0
589  if (x >= ~0UL / (HZ / USER_HZ))
590  return ~0UL;
591  return x * (HZ / USER_HZ);
592 #else
593  /* Don't worry about loss of precision here .. */
594  if (x >= ~0UL / HZ * USER_HZ)
595  return ~0UL;
596 
597  /* .. but do try to contain it here */
598  return div_u64((u64)x * HZ, USER_HZ);
599 #endif
600 }
602 
604 {
605 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
606 # if HZ < USER_HZ
607  x = div_u64(x * USER_HZ, HZ);
608 # elif HZ > USER_HZ
609  x = div_u64(x, HZ / USER_HZ);
610 # else
611  /* Nothing to do */
612 # endif
613 #else
614  /*
615  * There are better ways that don't overflow early,
616  * but even this doesn't overflow in hundreds of years
617  * in 64 bits, so..
618  */
619  x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
620 #endif
621  return x;
622 }
624 
626 {
627 #if (NSEC_PER_SEC % USER_HZ) == 0
628  return div_u64(x, NSEC_PER_SEC / USER_HZ);
629 #elif (USER_HZ % 512) == 0
630  return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
631 #else
632  /*
633  * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
634  * overflow after 64.99 years.
635  * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
636  */
637  return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
638 #endif
639 }
640 
655 {
656 #if (NSEC_PER_SEC % HZ) == 0
657  /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
658  return div_u64(n, NSEC_PER_SEC / HZ);
659 #elif (HZ % 512) == 0
660  /* overflow after 292 years if HZ = 1024 */
661  return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
662 #else
663  /*
664  * Generic case - optimized for cases where HZ is a multiple of 3.
665  * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
666  */
667  return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
668 #endif
669 }
670 
684 unsigned long nsecs_to_jiffies(u64 n)
685 {
686  return (unsigned long)nsecs_to_jiffies64(n);
687 }
688 
689 /*
690  * Add two timespec values and do a safety check for overflow.
691  * It's assumed that both values are valid (>= 0)
692  */
694  const struct timespec rhs)
695 {
696  struct timespec res;
697 
698  set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
699  lhs.tv_nsec + rhs.tv_nsec);
700 
701  if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
702  res.tv_sec = TIME_T_MAX;
703 
704  return res;
705 }