aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/time.c
blob: ba744cf80696203b65406c7aef8faae3a23048d0 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
/*
 *  linux/kernel/time.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  This file contains the interface functions for the various
 *  time related system calls: time, stime, gettimeofday, settimeofday,
 *			       adjtime
 */
/*
 * Modification history kernel/time.c
 *
 * 1993-09-02    Philip Gladstone
 *      Created file with time related functions from sched.c and adjtimex()
 * 1993-10-08    Torsten Duwe
 *      adjtime interface update and CMOS clock write code
 * 1995-08-13    Torsten Duwe
 *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
 * 1999-01-16    Ulrich Windl
 *	Introduced error checking for many cases in adjtimex().
 *	Updated NTP code according to technical memorandum Jan '96
 *	"A Kernel Model for Precision Timekeeping" by Dave Mills
 *	Allow time_constant larger than MAXTC(6) for NTP v4 (MAXTC == 10)
 *	(Even though the technical memorandum forbids it)
 * 2004-07-14	 Christoph Lameter
 *	Added getnstimeofday to allow the posix timer functions to return
 *	with nanosecond accuracy
 */

#include <linux/export.h>
#include <linux/timex.h>
#include <linux/capability.h>
#include <linux/clocksource.h>
#include <linux/errno.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/fs.h>
#include <linux/math64.h>
#include <linux/ptrace.h>

#include <asm/uaccess.h>
#include <asm/unistd.h>

#include "timeconst.h"

/*
 * The timezone where the local system is located.  Used as a default by some
 * programs who obtain this value by using gettimeofday.
 */
struct timezone sys_tz;

EXPORT_SYMBOL(sys_tz);

#ifdef __ARCH_WANT_SYS_TIME

/*
 * sys_time() can be implemented in user-level using
 * sys_gettimeofday().  Is this for backwards compatibility?  If so,
 * why not move it into the appropriate arch directory (for those
 * architectures that need it).
 */
SYSCALL_DEFINE1(time, time_t __user *, tloc)
{
	time_t i = get_seconds();

	if (tloc) {
		if (put_user(i,tloc))
			return -EFAULT;
	}
	force_successful_syscall_return();
	return i;
}

/*
 * sys_stime() can be implemented in user-level using
 * sys_settimeofday().  Is this for backwards compatibility?  If so,
 * why not move it into the appropriate arch directory (for those
 * architectures that need it).
 */

SYSCALL_DEFINE1(stime, time_t __user *, tptr)
{
	struct timespec tv;
	int err;

	if (get_user(tv.tv_sec, tptr))
		return -EFAULT;

	tv.tv_nsec = 0;

	err = security_settime(&tv, NULL);
	if (err)
		return err;

	do_settimeofday(&tv);
	return 0;
}

#endif /* __ARCH_WANT_SYS_TIME */

SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
		struct timezone __user *, tz)
{
	if (likely(tv != NULL)) {
		struct timeval ktv;
		do_gettimeofday(&ktv);
		if (copy_to_user(tv, &ktv, sizeof(ktv)))
			return -EFAULT;
	}
	if (unlikely(tz != NULL)) {
		if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
			return -EFAULT;
	}
	return 0;
}

/*
 * Adjust the time obtained from the CMOS to be UTC time instead of
 * local time.
 *
 * This is ugly, but preferable to the alternatives.  Otherwise we
 * would either need to write a program to do it in /etc/rc (and risk
 * confusion if the program gets run more than once; it would also be
 * hard to make the program warp the clock precisely n hours)  or
 * compile in the timezone information into the kernel.  Bad, bad....
 *
 *						- TYT, 1992-01-01
 *
 * The best thing to do is to keep the CMOS clock in universal time (UTC)
 * as real UNIX machines always do it. This avoids all headaches about
 * daylight saving times and warping kernel clocks.
 */
static inline void warp_clock(void)
{
	struct timespec adjust;

	adjust = current_kernel_time();
	adjust.tv_sec += sys_tz.tz_minuteswest * 60;
	do_settimeofday(&adjust);
}

/*
 * In case for some reason the CMOS clock has not already been running
 * in UTC, but in some local time: The first time we set the timezone,
 * we will warp the clock so that it is ticking UTC time instead of
 * local time. Presumably, if someone is setting the timezone then we
 * are running in an environment where the programs understand about
 * timezones. This should be done at boot time in the /etc/rc script,
 * as soon as possible, so that the clock can be set right. Otherwise,
 * various programs will get confused when the clock gets warped.
 */

int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz)
{
	static int firsttime = 1;
	int error = 0;

	if (tv && !timespec_valid(tv))
		return -EINVAL;

	error = security_settime(tv, tz);
	if (error)
		return error;

	if (tz) {
		sys_tz = *tz;
		update_vsyscall_tz();
		if (firsttime) {
			firsttime = 0;
			if (!tv)
				warp_clock();
		}
	}
	if (tv)
		return do_settimeofday(tv);
	return 0;
}

SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
		struct timezone __user *, tz)
{
	struct timeval user_tv;
	struct timespec	new_ts;
	struct timezone new_tz;

	if (tv) {
		if (copy_from_user(&user_tv, tv, sizeof(*tv)))
			return -EFAULT;
		new_ts.tv_sec = user_tv.tv_sec;
		new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
	}
	if (tz) {
		if (copy_from_user(&new_tz, tz, sizeof(*tz)))
			return -EFAULT;
	}

	return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
}

SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
{
	struct timex txc;		/* Local copy of parameter */
	int ret;

	/* Copy the user data space into the kernel copy
	 * structure. But bear in mind that the structures
	 * may change
	 */
	if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
		return -EFAULT;
	ret = do_adjtimex(&txc);
	return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
}

/**
 * current_fs_time - Return FS time
 * @sb: Superblock.
 *
 * Return the current time truncated to the time granularity supported by
 * the fs.
 */
struct timespec current_fs_time(struct super_block *sb)
{
	struct timespec now = current_kernel_time();
	return timespec_trunc(now, sb->s_time_gran);
}
EXPORT_SYMBOL(current_fs_time);

/*
 * Convert jiffies to milliseconds and back.
 *
 * Avoid unnecessary multiplications/divisions in the
 * two most common HZ cases:
 */
inline unsigned int jiffies_to_msecs(const unsigned long j)
{
#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
	return (MSEC_PER_SEC / HZ) * j;
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
	return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
	return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
# else
	return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_msecs);

inline unsigned int jiffies_to_usecs(const unsigned long j)
{
#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
	return (USEC_PER_SEC / HZ) * j;
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
	return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
	return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
# else
	return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_usecs);

/**
 * timespec_trunc - Truncate timespec to a granularity
 * @t: Timespec
 * @gran: Granularity in ns.
 *
 * Truncate a timespec to a granularity. gran must be smaller than a second.
 * Always rounds down.
 *
 * This function should be only used for timestamps returned by
 * current_kernel_time() or CURRENT_TIME, not with do_gettimeofday() because
 * it doesn't handle the better resolution of the latter.
 */
struct timespec timespec_trunc(struct timespec t, unsigned gran)
{
	/*
	 * Division is pretty slow so avoid it for common cases.
	 * Currently current_kernel_time() never returns better than
	 * jiffies resolution. Exploit that.
	 */
	if (gran <= jiffies_to_usecs(1) * 1000) {
		/* nothing */
	} else if (gran == 1000000000) {
		t.tv_nsec = 0;
	} else {
		t.tv_nsec -= t.tv_nsec % gran;
	}
	return t;
}
EXPORT_SYMBOL(timespec_trunc);

/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines where long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
unsigned long
mktime(const unsigned int year0, const unsigned int mon0,
       const unsigned int day, const unsigned int hour,
       const unsigned int min, const unsigned int sec)
{
	unsigned int mon = mon0, year = year0;

	/* 1..12 -> 11,12,1..10 */
	if (0 >= (int) (mon -= 2)) {
		mon += 12;	/* Puts Feb last since it has leap day */
		year -= 1;
	}

	return ((((unsigned long)
		  (year/4 - year/100 + year/400 + 367*mon/12 + day) +
		  year*365 - 719499
	    )*24 + hour /* now have hours */
	  )*60 + min /* now have minutes */
	)*60 + sec; /* finally seconds */
}

EXPORT_SYMBOL(mktime);

/**
 * set_normalized_timespec - set timespec sec and nsec parts and normalize
 *
 * @ts:		pointer to timespec variable to be set
 * @sec:	seconds to set
 * @nsec:	nanoseconds to set
 *
 * Set seconds and nanoseconds field of a timespec variable and
 * normalize to the timespec storage format
 *
 * Note: The tv_nsec part is always in the range of
 *	0 <= tv_nsec < NSEC_PER_SEC
 * For negative values only the tv_sec field is negative !
 */
void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
{
	while (nsec >= NSEC_PER_SEC) {
		/*
		 * The following asm() prevents the compiler from
		 * optimising this loop into a modulo operation. See
		 * also __iter_div_u64_rem() in include/linux/time.h
		 */
		asm("" : "+rm"(nsec));
		nsec -= NSEC_PER_SEC;
		++sec;
	}
	while (nsec < 0) {
		asm("" : "+rm"(nsec));
		nsec += NSEC_PER_SEC;
		--sec;
	}
	ts->tv_sec = sec;
	ts->tv_nsec = nsec;
}
EXPORT_SYMBOL(set_normalized_timespec);

/**
 * ns_to_timespec - Convert nanoseconds to timespec
 * @nsec:       the nanoseconds value to be converted
 *
 * Returns the timespec representation of the nsec parameter.
 */
struct timespec ns_to_timespec(const s64 nsec)
{
	struct timespec ts;
	s32 rem;

	if (!nsec)
		return (struct timespec) {0, 0};

	ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
	if (unlikely(rem < 0)) {
		ts.tv_sec--;
		rem += NSEC_PER_SEC;
	}
	ts.tv_nsec = rem;

	return ts;
}
EXPORT_SYMBOL(ns_to_timespec);

/**
 * ns_to_timeval - Convert nanoseconds to timeval
 * @nsec:       the nanoseconds value to be converted
 *
 * Returns the timeval representation of the nsec parameter.
 */
struct timeval ns_to_timeval(const s64 nsec)
{
	struct timespec ts = ns_to_timespec(nsec);
	struct timeval tv;

	tv.tv_sec = ts.tv_sec;
	tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;

	return tv;
}
EXPORT_SYMBOL(ns_to_timeval);

/*
 * When we convert to jiffies then we interpret incoming values
 * the following way:
 *
 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 *
 * - 'too large' values [that would result in larger than
 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 *
 * - all other values are converted to jiffies by either multiplying
 *   the input value by a factor or dividing it with a factor
 *
 * We must also be careful about 32-bit overflows.
 */
unsigned long msecs_to_jiffies(const unsigned int m)
{
	/*
	 * Negative value, means infinite timeout:
	 */
	if ((int)m < 0)
		return MAX_JIFFY_OFFSET;

#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
	/*
	 * HZ is equal to or smaller than 1000, and 1000 is a nice
	 * round multiple of HZ, divide with the factor between them,
	 * but round upwards:
	 */
	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
	/*
	 * HZ is larger than 1000, and HZ is a nice round multiple of
	 * 1000 - simply multiply with the factor between them.
	 *
	 * But first make sure the multiplication result cannot
	 * overflow:
	 */
	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;

	return m * (HZ / MSEC_PER_SEC);
#else
	/*
	 * Generic case - multiply, round and divide. But first
	 * check that if we are doing a net multiplication, that
	 * we wouldn't overflow:
	 */
	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;

	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
		>> MSEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(msecs_to_jiffies);

unsigned long usecs_to_jiffies(const unsigned int u)
{
	if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;
#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
	return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
	return u * (HZ / USEC_PER_SEC);
#else
	return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
		>> USEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(usecs_to_jiffies);

/*
 * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
 * that a remainder subtract here would not do the right thing as the
 * resolution values don't fall on second boundries.  I.e. the line:
 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
 *
 * Rather, we just shift the bits off the right.
 *
 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
 * value to a scaled second value.
 */
unsigned long
timespec_to_jiffies(const struct timespec *value)
{
	unsigned long sec = value->tv_sec;
	long nsec = value->tv_nsec + TICK_NSEC - 1;

	if (sec >= MAX_SEC_IN_JIFFIES){
		sec = MAX_SEC_IN_JIFFIES;
		nsec = 0;
	}
	return (((u64)sec * SEC_CONVERSION) +
		(((u64)nsec * NSEC_CONVERSION) >>
		 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;

}
EXPORT_SYMBOL(timespec_to_jiffies);

void
jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
{
	/*
	 * Convert jiffies to nanoseconds and separate with
	 * one divide.
	 */
	u32 rem;
	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
				    NSEC_PER_SEC, &rem);
	value->tv_nsec = rem;
}
EXPORT_SYMBOL(jiffies_to_timespec);

/* Same for "timeval"
 *
 * Well, almost.  The problem here is that the real system resolution is
 * in nanoseconds and the value being converted is in micro seconds.
 * Also for some machines (those that use HZ = 1024, in-particular),
 * there is a LARGE error in the tick size in microseconds.

 * The solution we use is to do the rounding AFTER we convert the
 * microsecond part.  Thus the USEC_ROUND, the bits to be shifted off.
 * Instruction wise, this should cost only an additional add with carry
 * instruction above the way it was done above.
 */
unsigned long
timeval_to_jiffies(const struct timeval *value)
{
	unsigned long sec = value->tv_sec;
	long usec = value->tv_usec;

	if (sec >= MAX_SEC_IN_JIFFIES){
		sec = MAX_SEC_IN_JIFFIES;
		usec = 0;
	}
	return (((u64)sec * SEC_CONVERSION) +
		(((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
		 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
}
EXPORT_SYMBOL(timeval_to_jiffies);

void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
{
	/*
	 * Convert jiffies to nanoseconds and separate with
	 * one divide.
	 */
	u32 rem;

	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
				    NSEC_PER_SEC, &rem);
	value->tv_usec = rem / NSEC_PER_USEC;
}
EXPORT_SYMBOL(jiffies_to_timeval);

/*
 * Convert jiffies/jiffies_64 to clock_t and back.
 */
clock_t jiffies_to_clock_t(unsigned long x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
# if HZ < USER_HZ
	return x * (USER_HZ / HZ);
# else
	return x / (HZ / USER_HZ);
# endif
#else
	return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
#endif
}
EXPORT_SYMBOL(jiffies_to_clock_t);

unsigned long clock_t_to_jiffies(unsigned long x)
{
#if (HZ % USER_HZ)==0
	if (x >= ~0UL / (HZ / USER_HZ))
		return ~0UL;
	return x * (HZ / USER_HZ);
#else
	/* Don't worry about loss of precision here .. */
	if (x >= ~0UL / HZ * USER_HZ)
		return ~0UL;

	/* .. but do try to contain it here */
	return div_u64((u64)x * HZ, USER_HZ);
#endif
}
EXPORT_SYMBOL(clock_t_to_jiffies);

u64 jiffies_64_to_clock_t(u64 x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
# if HZ < USER_HZ
	x = div_u64(x * USER_HZ, HZ);
# elif HZ > USER_HZ
	x = div_u64(x, HZ / USER_HZ);
# else
	/* Nothing to do */
# endif
#else
	/*
	 * There are better ways that don't overflow early,
	 * but even this doesn't overflow in hundreds of years
	 * in 64 bits, so..
	 */
	x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
#endif
	return x;
}
EXPORT_SYMBOL(jiffies_64_to_clock_t);

u64 nsec_to_clock_t(u64 x)
{
#if (NSEC_PER_SEC % USER_HZ) == 0
	return div_u64(x, NSEC_PER_SEC / USER_HZ);
#elif (USER_HZ % 512) == 0
	return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
#else
	/*
         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
         * overflow after 64.99 years.
         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
         */
	return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
#endif
}

/**
 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
 *
 * @n:	nsecs in u64
 *
 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 * for scheduler, not for use in device drivers to calculate timeout value.
 *
 * note:
 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 */
u64 nsecs_to_jiffies64(u64 n)
{
#if (NSEC_PER_SEC % HZ) == 0
	/* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
	return div_u64(n, NSEC_PER_SEC / HZ);
#elif (HZ % 512) == 0
	/* overflow after 292 years if HZ = 1024 */
	return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
#else
	/*
	 * Generic case - optimized for cases where HZ is a multiple of 3.
	 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
	 */
	return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
#endif
}

/**
 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
 *
 * @n:	nsecs in u64
 *
 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
 * for scheduler, not for use in device drivers to calculate timeout value.
 *
 * note:
 *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
 *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
 */
unsigned long nsecs_to_jiffies(u64 n)
{
	return (unsigned long)nsecs_to_jiffies64(n);
}

/*
 * Add two timespec values and do a safety check for overflow.
 * It's assumed that both values are valid (>= 0)
 */
struct timespec timespec_add_safe(const struct timespec lhs,
				  const struct timespec rhs)
{
	struct timespec res;

	set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec,
				lhs.tv_nsec + rhs.tv_nsec);

	if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec)
		res.tv_sec = TIME_T_MAX;

	return res;
}