m68k: kill skb_copy_from_linear_data compiler warnings
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / time.c
blobba18ec4899bd92fe23a93716daf495bd2876025e
1 /*
2 * linux/kernel/time.c
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,
8 * adjtime
9 */
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/module.h>
31 #include <linux/timex.h>
32 #include <linux/capability.h>
33 #include <linux/errno.h>
34 #include <linux/smp_lock.h>
35 #include <linux/syscalls.h>
36 #include <linux/security.h>
37 #include <linux/fs.h>
38 #include <linux/module.h>
40 #include <asm/uaccess.h>
41 #include <asm/unistd.h>
43 /*
44 * The timezone where the local system is located. Used as a default by some
45 * programs who obtain this value by using gettimeofday.
47 struct timezone sys_tz;
49 EXPORT_SYMBOL(sys_tz);
51 #ifdef __ARCH_WANT_SYS_TIME
54 * sys_time() can be implemented in user-level using
55 * sys_gettimeofday(). Is this for backwards compatibility? If so,
56 * why not move it into the appropriate arch directory (for those
57 * architectures that need it).
59 asmlinkage long sys_time(time_t __user * tloc)
61 time_t i;
62 struct timeval tv;
64 do_gettimeofday(&tv);
65 i = tv.tv_sec;
67 if (tloc) {
68 if (put_user(i,tloc))
69 i = -EFAULT;
71 return i;
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 asmlinkage long sys_stime(time_t __user *tptr)
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;
99 #endif /* __ARCH_WANT_SYS_TIME */
101 asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __user *tz)
103 if (likely(tv != NULL)) {
104 struct timeval ktv;
105 do_gettimeofday(&ktv);
106 if (copy_to_user(tv, &ktv, sizeof(ktv)))
107 return -EFAULT;
109 if (unlikely(tz != NULL)) {
110 if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
111 return -EFAULT;
113 return 0;
117 * Adjust the time obtained from the CMOS to be UTC time instead of
118 * local time.
120 * This is ugly, but preferable to the alternatives. Otherwise we
121 * would either need to write a program to do it in /etc/rc (and risk
122 * confusion if the program gets run more than once; it would also be
123 * hard to make the program warp the clock precisely n hours) or
124 * compile in the timezone information into the kernel. Bad, bad....
126 * - TYT, 1992-01-01
128 * The best thing to do is to keep the CMOS clock in universal time (UTC)
129 * as real UNIX machines always do it. This avoids all headaches about
130 * daylight saving times and warping kernel clocks.
132 static inline void warp_clock(void)
134 write_seqlock_irq(&xtime_lock);
135 wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
136 xtime.tv_sec += sys_tz.tz_minuteswest * 60;
137 time_interpolator_reset();
138 write_sequnlock_irq(&xtime_lock);
139 clock_was_set();
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.
153 int do_sys_settimeofday(struct timespec *tv, struct timezone *tz)
155 static int firsttime = 1;
156 int error = 0;
158 if (tv && !timespec_valid(tv))
159 return -EINVAL;
161 error = security_settime(tv, tz);
162 if (error)
163 return error;
165 if (tz) {
166 /* SMP safe, global irq locking makes it work. */
167 sys_tz = *tz;
168 if (firsttime) {
169 firsttime = 0;
170 if (!tv)
171 warp_clock();
174 if (tv)
176 /* SMP safe, again the code in arch/foo/time.c should
177 * globally block out interrupts when it runs.
179 return do_settimeofday(tv);
181 return 0;
184 asmlinkage long sys_settimeofday(struct timeval __user *tv,
185 struct timezone __user *tz)
187 struct timeval user_tv;
188 struct timespec new_ts;
189 struct timezone new_tz;
191 if (tv) {
192 if (copy_from_user(&user_tv, tv, sizeof(*tv)))
193 return -EFAULT;
194 new_ts.tv_sec = user_tv.tv_sec;
195 new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
197 if (tz) {
198 if (copy_from_user(&new_tz, tz, sizeof(*tz)))
199 return -EFAULT;
202 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
205 asmlinkage long sys_adjtimex(struct timex __user *txc_p)
207 struct timex txc; /* Local copy of parameter */
208 int ret;
210 /* Copy the user data space into the kernel copy
211 * structure. But bear in mind that the structures
212 * may change
214 if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
215 return -EFAULT;
216 ret = do_adjtimex(&txc);
217 return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
220 inline struct timespec current_kernel_time(void)
222 struct timespec now;
223 unsigned long seq;
225 do {
226 seq = read_seqbegin(&xtime_lock);
228 now = xtime;
229 } while (read_seqretry(&xtime_lock, seq));
231 return now;
234 EXPORT_SYMBOL(current_kernel_time);
237 * current_fs_time - Return FS time
238 * @sb: Superblock.
240 * Return the current time truncated to the time granularity supported by
241 * the fs.
243 struct timespec current_fs_time(struct super_block *sb)
245 struct timespec now = current_kernel_time();
246 return timespec_trunc(now, sb->s_time_gran);
248 EXPORT_SYMBOL(current_fs_time);
251 * timespec_trunc - Truncate timespec to a granularity
252 * @t: Timespec
253 * @gran: Granularity in ns.
255 * Truncate a timespec to a granularity. gran must be smaller than a second.
256 * Always rounds down.
258 * This function should be only used for timestamps returned by
259 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
260 * it doesn't handle the better resolution of the later.
262 struct timespec timespec_trunc(struct timespec t, unsigned gran)
265 * Division is pretty slow so avoid it for common cases.
266 * Currently current_kernel_time() never returns better than
267 * jiffies resolution. Exploit that.
269 if (gran <= jiffies_to_usecs(1) * 1000) {
270 /* nothing */
271 } else if (gran == 1000000000) {
272 t.tv_nsec = 0;
273 } else {
274 t.tv_nsec -= t.tv_nsec % gran;
276 return t;
278 EXPORT_SYMBOL(timespec_trunc);
280 #ifdef CONFIG_TIME_INTERPOLATION
281 void getnstimeofday (struct timespec *tv)
283 unsigned long seq,sec,nsec;
285 do {
286 seq = read_seqbegin(&xtime_lock);
287 sec = xtime.tv_sec;
288 nsec = xtime.tv_nsec+time_interpolator_get_offset();
289 } while (unlikely(read_seqretry(&xtime_lock, seq)));
291 while (unlikely(nsec >= NSEC_PER_SEC)) {
292 nsec -= NSEC_PER_SEC;
293 ++sec;
295 tv->tv_sec = sec;
296 tv->tv_nsec = nsec;
298 EXPORT_SYMBOL_GPL(getnstimeofday);
300 int do_settimeofday (struct timespec *tv)
302 time_t wtm_sec, sec = tv->tv_sec;
303 long wtm_nsec, nsec = tv->tv_nsec;
305 if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
306 return -EINVAL;
308 write_seqlock_irq(&xtime_lock);
310 wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
311 wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
313 set_normalized_timespec(&xtime, sec, nsec);
314 set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
316 time_adjust = 0; /* stop active adjtime() */
317 time_status |= STA_UNSYNC;
318 time_maxerror = NTP_PHASE_LIMIT;
319 time_esterror = NTP_PHASE_LIMIT;
320 time_interpolator_reset();
322 write_sequnlock_irq(&xtime_lock);
323 clock_was_set();
324 return 0;
326 EXPORT_SYMBOL(do_settimeofday);
328 void do_gettimeofday (struct timeval *tv)
330 unsigned long seq, nsec, usec, sec, offset;
331 do {
332 seq = read_seqbegin(&xtime_lock);
333 offset = time_interpolator_get_offset();
334 sec = xtime.tv_sec;
335 nsec = xtime.tv_nsec;
336 } while (unlikely(read_seqretry(&xtime_lock, seq)));
338 usec = (nsec + offset) / 1000;
340 while (unlikely(usec >= USEC_PER_SEC)) {
341 usec -= USEC_PER_SEC;
342 ++sec;
345 tv->tv_sec = sec;
346 tv->tv_usec = usec;
349 EXPORT_SYMBOL(do_gettimeofday);
352 #else
353 #ifndef CONFIG_GENERIC_TIME
355 * Simulate gettimeofday using do_gettimeofday which only allows a timeval
356 * and therefore only yields usec accuracy
358 void getnstimeofday(struct timespec *tv)
360 struct timeval x;
362 do_gettimeofday(&x);
363 tv->tv_sec = x.tv_sec;
364 tv->tv_nsec = x.tv_usec * NSEC_PER_USEC;
366 EXPORT_SYMBOL_GPL(getnstimeofday);
367 #endif
368 #endif
370 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
371 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
372 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
374 * [For the Julian calendar (which was used in Russia before 1917,
375 * Britain & colonies before 1752, anywhere else before 1582,
376 * and is still in use by some communities) leave out the
377 * -year/100+year/400 terms, and add 10.]
379 * This algorithm was first published by Gauss (I think).
381 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
382 * machines were long is 32-bit! (However, as time_t is signed, we
383 * will already get problems at other places on 2038-01-19 03:14:08)
385 unsigned long
386 mktime(const unsigned int year0, const unsigned int mon0,
387 const unsigned int day, const unsigned int hour,
388 const unsigned int min, const unsigned int sec)
390 unsigned int mon = mon0, year = year0;
392 /* 1..12 -> 11,12,1..10 */
393 if (0 >= (int) (mon -= 2)) {
394 mon += 12; /* Puts Feb last since it has leap day */
395 year -= 1;
398 return ((((unsigned long)
399 (year/4 - year/100 + year/400 + 367*mon/12 + day) +
400 year*365 - 719499
401 )*24 + hour /* now have hours */
402 )*60 + min /* now have minutes */
403 )*60 + sec; /* finally seconds */
406 EXPORT_SYMBOL(mktime);
409 * set_normalized_timespec - set timespec sec and nsec parts and normalize
411 * @ts: pointer to timespec variable to be set
412 * @sec: seconds to set
413 * @nsec: nanoseconds to set
415 * Set seconds and nanoseconds field of a timespec variable and
416 * normalize to the timespec storage format
418 * Note: The tv_nsec part is always in the range of
419 * 0 <= tv_nsec < NSEC_PER_SEC
420 * For negative values only the tv_sec field is negative !
422 void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
424 while (nsec >= NSEC_PER_SEC) {
425 nsec -= NSEC_PER_SEC;
426 ++sec;
428 while (nsec < 0) {
429 nsec += NSEC_PER_SEC;
430 --sec;
432 ts->tv_sec = sec;
433 ts->tv_nsec = nsec;
437 * ns_to_timespec - Convert nanoseconds to timespec
438 * @nsec: the nanoseconds value to be converted
440 * Returns the timespec representation of the nsec parameter.
442 struct timespec ns_to_timespec(const s64 nsec)
444 struct timespec ts;
446 if (!nsec)
447 return (struct timespec) {0, 0};
449 ts.tv_sec = div_long_long_rem_signed(nsec, NSEC_PER_SEC, &ts.tv_nsec);
450 if (unlikely(nsec < 0))
451 set_normalized_timespec(&ts, ts.tv_sec, ts.tv_nsec);
453 return ts;
455 EXPORT_SYMBOL(ns_to_timespec);
458 * ns_to_timeval - Convert nanoseconds to timeval
459 * @nsec: the nanoseconds value to be converted
461 * Returns the timeval representation of the nsec parameter.
463 struct timeval ns_to_timeval(const s64 nsec)
465 struct timespec ts = ns_to_timespec(nsec);
466 struct timeval tv;
468 tv.tv_sec = ts.tv_sec;
469 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
471 return tv;
473 EXPORT_SYMBOL(ns_to_timeval);
476 * Convert jiffies to milliseconds and back.
478 * Avoid unnecessary multiplications/divisions in the
479 * two most common HZ cases:
481 unsigned int jiffies_to_msecs(const unsigned long j)
483 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
484 return (MSEC_PER_SEC / HZ) * j;
485 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
486 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
487 #else
488 return (j * MSEC_PER_SEC) / HZ;
489 #endif
491 EXPORT_SYMBOL(jiffies_to_msecs);
493 unsigned int jiffies_to_usecs(const unsigned long j)
495 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
496 return (USEC_PER_SEC / HZ) * j;
497 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
498 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
499 #else
500 return (j * USEC_PER_SEC) / HZ;
501 #endif
503 EXPORT_SYMBOL(jiffies_to_usecs);
506 * When we convert to jiffies then we interpret incoming values
507 * the following way:
509 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
511 * - 'too large' values [that would result in larger than
512 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
514 * - all other values are converted to jiffies by either multiplying
515 * the input value by a factor or dividing it with a factor
517 * We must also be careful about 32-bit overflows.
519 unsigned long msecs_to_jiffies(const unsigned int m)
522 * Negative value, means infinite timeout:
524 if ((int)m < 0)
525 return MAX_JIFFY_OFFSET;
527 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
529 * HZ is equal to or smaller than 1000, and 1000 is a nice
530 * round multiple of HZ, divide with the factor between them,
531 * but round upwards:
533 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
534 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
536 * HZ is larger than 1000, and HZ is a nice round multiple of
537 * 1000 - simply multiply with the factor between them.
539 * But first make sure the multiplication result cannot
540 * overflow:
542 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
543 return MAX_JIFFY_OFFSET;
545 return m * (HZ / MSEC_PER_SEC);
546 #else
548 * Generic case - multiply, round and divide. But first
549 * check that if we are doing a net multiplication, that
550 * we wouldnt overflow:
552 if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
553 return MAX_JIFFY_OFFSET;
555 return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;
556 #endif
558 EXPORT_SYMBOL(msecs_to_jiffies);
560 unsigned long usecs_to_jiffies(const unsigned int u)
562 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
563 return MAX_JIFFY_OFFSET;
564 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
565 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
566 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
567 return u * (HZ / USEC_PER_SEC);
568 #else
569 return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC;
570 #endif
572 EXPORT_SYMBOL(usecs_to_jiffies);
575 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
576 * that a remainder subtract here would not do the right thing as the
577 * resolution values don't fall on second boundries. I.e. the line:
578 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
580 * Rather, we just shift the bits off the right.
582 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
583 * value to a scaled second value.
585 unsigned long
586 timespec_to_jiffies(const struct timespec *value)
588 unsigned long sec = value->tv_sec;
589 long nsec = value->tv_nsec + TICK_NSEC - 1;
591 if (sec >= MAX_SEC_IN_JIFFIES){
592 sec = MAX_SEC_IN_JIFFIES;
593 nsec = 0;
595 return (((u64)sec * SEC_CONVERSION) +
596 (((u64)nsec * NSEC_CONVERSION) >>
597 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
600 EXPORT_SYMBOL(timespec_to_jiffies);
602 void
603 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
606 * Convert jiffies to nanoseconds and separate with
607 * one divide.
609 u64 nsec = (u64)jiffies * TICK_NSEC;
610 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
612 EXPORT_SYMBOL(jiffies_to_timespec);
614 /* Same for "timeval"
616 * Well, almost. The problem here is that the real system resolution is
617 * in nanoseconds and the value being converted is in micro seconds.
618 * Also for some machines (those that use HZ = 1024, in-particular),
619 * there is a LARGE error in the tick size in microseconds.
621 * The solution we use is to do the rounding AFTER we convert the
622 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
623 * Instruction wise, this should cost only an additional add with carry
624 * instruction above the way it was done above.
626 unsigned long
627 timeval_to_jiffies(const struct timeval *value)
629 unsigned long sec = value->tv_sec;
630 long usec = value->tv_usec;
632 if (sec >= MAX_SEC_IN_JIFFIES){
633 sec = MAX_SEC_IN_JIFFIES;
634 usec = 0;
636 return (((u64)sec * SEC_CONVERSION) +
637 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
638 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
640 EXPORT_SYMBOL(timeval_to_jiffies);
642 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
645 * Convert jiffies to nanoseconds and separate with
646 * one divide.
648 u64 nsec = (u64)jiffies * TICK_NSEC;
649 long tv_usec;
651 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec);
652 tv_usec /= NSEC_PER_USEC;
653 value->tv_usec = tv_usec;
655 EXPORT_SYMBOL(jiffies_to_timeval);
658 * Convert jiffies/jiffies_64 to clock_t and back.
660 clock_t jiffies_to_clock_t(long x)
662 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
663 return x / (HZ / USER_HZ);
664 #else
665 u64 tmp = (u64)x * TICK_NSEC;
666 do_div(tmp, (NSEC_PER_SEC / USER_HZ));
667 return (long)tmp;
668 #endif
670 EXPORT_SYMBOL(jiffies_to_clock_t);
672 unsigned long clock_t_to_jiffies(unsigned long x)
674 #if (HZ % USER_HZ)==0
675 if (x >= ~0UL / (HZ / USER_HZ))
676 return ~0UL;
677 return x * (HZ / USER_HZ);
678 #else
679 u64 jif;
681 /* Don't worry about loss of precision here .. */
682 if (x >= ~0UL / HZ * USER_HZ)
683 return ~0UL;
685 /* .. but do try to contain it here */
686 jif = x * (u64) HZ;
687 do_div(jif, USER_HZ);
688 return jif;
689 #endif
691 EXPORT_SYMBOL(clock_t_to_jiffies);
693 u64 jiffies_64_to_clock_t(u64 x)
695 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
696 do_div(x, HZ / USER_HZ);
697 #else
699 * There are better ways that don't overflow early,
700 * but even this doesn't overflow in hundreds of years
701 * in 64 bits, so..
703 x *= TICK_NSEC;
704 do_div(x, (NSEC_PER_SEC / USER_HZ));
705 #endif
706 return x;
709 EXPORT_SYMBOL(jiffies_64_to_clock_t);
711 u64 nsec_to_clock_t(u64 x)
713 #if (NSEC_PER_SEC % USER_HZ) == 0
714 do_div(x, (NSEC_PER_SEC / USER_HZ));
715 #elif (USER_HZ % 512) == 0
716 x *= USER_HZ/512;
717 do_div(x, (NSEC_PER_SEC / 512));
718 #else
720 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
721 * overflow after 64.99 years.
722 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
724 x *= 9;
725 do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) /
726 USER_HZ));
727 #endif
728 return x;
731 #if (BITS_PER_LONG < 64)
732 u64 get_jiffies_64(void)
734 unsigned long seq;
735 u64 ret;
737 do {
738 seq = read_seqbegin(&xtime_lock);
739 ret = jiffies_64;
740 } while (read_seqretry(&xtime_lock, seq));
741 return ret;
744 EXPORT_SYMBOL(get_jiffies_64);
745 #endif
747 EXPORT_SYMBOL(jiffies);