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/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 28 */ 29 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> 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 #include "timekeeping.h" 46 47 /* 48 * The timezone where the local system is located. Used as a default by some 49 * programs who obtain this value by using gettimeofday. 50 */ 51 struct timezone sys_tz; 52 53 EXPORT_SYMBOL(sys_tz); 54 55 #ifdef __ARCH_WANT_SYS_TIME 56 57 /* 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). 62 */ 63 SYSCALL_DEFINE1(time, time_t __user *, tloc) 64 { 65 time_t i = get_seconds(); 66 67 if (tloc) { 68 if (put_user(i,tloc)) 69 return -EFAULT; 70 } 71 force_successful_syscall_return(); 72 return i; 73 } 74 75 /* 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). 80 */ 81 82 SYSCALL_DEFINE1(stime, time_t __user *, tptr) 83 { 84 struct timespec tv; 85 int err; 86 87 if (get_user(tv.tv_sec, tptr)) 88 return -EFAULT; 89 90 tv.tv_nsec = 0; 91 92 err = security_settime(&tv, NULL); 93 if (err) 94 return err; 95 96 do_settimeofday(&tv); 97 return 0; 98 } 99 100 #endif /* __ARCH_WANT_SYS_TIME */ 101 102 SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv, 103 struct timezone __user *, tz) 104 { 105 if (likely(tv != NULL)) { 106 struct timeval ktv; 107 do_gettimeofday(&ktv); 108 if (copy_to_user(tv, &ktv, sizeof(ktv))) 109 return -EFAULT; 110 } 111 if (unlikely(tz != NULL)) { 112 if (copy_to_user(tz, &sys_tz, sizeof(sys_tz))) 113 return -EFAULT; 114 } 115 return 0; 116 } 117 118 /* 119 * Indicates if there is an offset between the system clock and the hardware 120 * clock/persistent clock/rtc. 121 */ 122 int persistent_clock_is_local; 123 124 /* 125 * Adjust the time obtained from the CMOS to be UTC time instead of 126 * local time. 127 * 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.... 133 * 134 * - TYT, 1992-01-01 135 * 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. 139 */ 140 static inline void warp_clock(void) 141 { 142 if (sys_tz.tz_minuteswest != 0) { 143 struct timespec adjust; 144 145 persistent_clock_is_local = 1; 146 adjust.tv_sec = sys_tz.tz_minuteswest * 60; 147 adjust.tv_nsec = 0; 148 timekeeping_inject_offset(&adjust); 149 } 150 } 151 152 /* 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. 161 */ 162 163 int do_sys_settimeofday(const struct timespec *tv, const struct timezone *tz) 164 { 165 static int firsttime = 1; 166 int error = 0; 167 168 if (tv && !timespec_valid(tv)) 169 return -EINVAL; 170 171 error = security_settime(tv, tz); 172 if (error) 173 return error; 174 175 if (tz) { 176 sys_tz = *tz; 177 update_vsyscall_tz(); 178 if (firsttime) { 179 firsttime = 0; 180 if (!tv) 181 warp_clock(); 182 } 183 } 184 if (tv) 185 return do_settimeofday(tv); 186 return 0; 187 } 188 189 SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv, 190 struct timezone __user *, tz) 191 { 192 struct timeval user_tv; 193 struct timespec new_ts; 194 struct timezone new_tz; 195 196 if (tv) { 197 if (copy_from_user(&user_tv, tv, sizeof(*tv))) 198 return -EFAULT; 199 new_ts.tv_sec = user_tv.tv_sec; 200 new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC; 201 } 202 if (tz) { 203 if (copy_from_user(&new_tz, tz, sizeof(*tz))) 204 return -EFAULT; 205 } 206 207 return do_sys_settimeofday(tv ? &new_ts : NULL, tz ? &new_tz : NULL); 208 } 209 210 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p) 211 { 212 struct timex txc; /* Local copy of parameter */ 213 int ret; 214 215 /* Copy the user data space into the kernel copy 216 * structure. But bear in mind that the structures 217 * may change 218 */ 219 if(copy_from_user(&txc, txc_p, sizeof(struct timex))) 220 return -EFAULT; 221 ret = do_adjtimex(&txc); 222 return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret; 223 } 224 225 /** 226 * current_fs_time - Return FS time 227 * @sb: Superblock. 228 * 229 * Return the current time truncated to the time granularity supported by 230 * the fs. 231 */ 232 struct timespec current_fs_time(struct super_block *sb) 233 { 234 struct timespec now = current_kernel_time(); 235 return timespec_trunc(now, sb->s_time_gran); 236 } 237 EXPORT_SYMBOL(current_fs_time); 238 239 /* 240 * Convert jiffies to milliseconds and back. 241 * 242 * Avoid unnecessary multiplications/divisions in the 243 * two most common HZ cases: 244 */ 245 unsigned int jiffies_to_msecs(const unsigned long j) 246 { 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); 251 #else 252 # if BITS_PER_LONG == 32 253 return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32; 254 # else 255 return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN; 256 # endif 257 #endif 258 } 259 EXPORT_SYMBOL(jiffies_to_msecs); 260 261 unsigned int jiffies_to_usecs(const unsigned long j) 262 { 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); 267 #else 268 # if BITS_PER_LONG == 32 269 return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32; 270 # else 271 return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN; 272 # endif 273 #endif 274 } 275 EXPORT_SYMBOL(jiffies_to_usecs); 276 277 /** 278 * timespec_trunc - Truncate timespec to a granularity 279 * @t: Timespec 280 * @gran: Granularity in ns. 281 * 282 * Truncate a timespec to a granularity. gran must be smaller than a second. 283 * Always rounds down. 284 * 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. 288 */ 289 struct timespec timespec_trunc(struct timespec t, unsigned gran) 290 { 291 /* 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. 295 */ 296 if (gran <= jiffies_to_usecs(1) * 1000) { 297 /* nothing */ 298 } else if (gran == 1000000000) { 299 t.tv_nsec = 0; 300 } else { 301 t.tv_nsec -= t.tv_nsec % gran; 302 } 303 return t; 304 } 305 EXPORT_SYMBOL(timespec_trunc); 306 307 /* 308 * mktime64 - Converts date to seconds. 309 * Converts Gregorian date to seconds since 1970-01-01 00:00:00. 310 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59 311 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59. 312 * 313 * [For the Julian calendar (which was used in Russia before 1917, 314 * Britain & colonies before 1752, anywhere else before 1582, 315 * and is still in use by some communities) leave out the 316 * -year/100+year/400 terms, and add 10.] 317 * 318 * This algorithm was first published by Gauss (I think). 319 */ 320 time64_t mktime64(const unsigned int year0, const unsigned int mon0, 321 const unsigned int day, const unsigned int hour, 322 const unsigned int min, const unsigned int sec) 323 { 324 unsigned int mon = mon0, year = year0; 325 326 /* 1..12 -> 11,12,1..10 */ 327 if (0 >= (int) (mon -= 2)) { 328 mon += 12; /* Puts Feb last since it has leap day */ 329 year -= 1; 330 } 331 332 return ((((time64_t) 333 (year/4 - year/100 + year/400 + 367*mon/12 + day) + 334 year*365 - 719499 335 )*24 + hour /* now have hours */ 336 )*60 + min /* now have minutes */ 337 )*60 + sec; /* finally seconds */ 338 } 339 EXPORT_SYMBOL(mktime64); 340 341 /** 342 * set_normalized_timespec - set timespec sec and nsec parts and normalize 343 * 344 * @ts: pointer to timespec variable to be set 345 * @sec: seconds to set 346 * @nsec: nanoseconds to set 347 * 348 * Set seconds and nanoseconds field of a timespec variable and 349 * normalize to the timespec storage format 350 * 351 * Note: The tv_nsec part is always in the range of 352 * 0 <= tv_nsec < NSEC_PER_SEC 353 * For negative values only the tv_sec field is negative ! 354 */ 355 void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec) 356 { 357 while (nsec >= NSEC_PER_SEC) { 358 /* 359 * The following asm() prevents the compiler from 360 * optimising this loop into a modulo operation. See 361 * also __iter_div_u64_rem() in include/linux/time.h 362 */ 363 asm("" : "+rm"(nsec)); 364 nsec -= NSEC_PER_SEC; 365 ++sec; 366 } 367 while (nsec < 0) { 368 asm("" : "+rm"(nsec)); 369 nsec += NSEC_PER_SEC; 370 --sec; 371 } 372 ts->tv_sec = sec; 373 ts->tv_nsec = nsec; 374 } 375 EXPORT_SYMBOL(set_normalized_timespec); 376 377 /** 378 * ns_to_timespec - Convert nanoseconds to timespec 379 * @nsec: the nanoseconds value to be converted 380 * 381 * Returns the timespec representation of the nsec parameter. 382 */ 383 struct timespec ns_to_timespec(const s64 nsec) 384 { 385 struct timespec ts; 386 s32 rem; 387 388 if (!nsec) 389 return (struct timespec) {0, 0}; 390 391 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem); 392 if (unlikely(rem < 0)) { 393 ts.tv_sec--; 394 rem += NSEC_PER_SEC; 395 } 396 ts.tv_nsec = rem; 397 398 return ts; 399 } 400 EXPORT_SYMBOL(ns_to_timespec); 401 402 /** 403 * ns_to_timeval - Convert nanoseconds to timeval 404 * @nsec: the nanoseconds value to be converted 405 * 406 * Returns the timeval representation of the nsec parameter. 407 */ 408 struct timeval ns_to_timeval(const s64 nsec) 409 { 410 struct timespec ts = ns_to_timespec(nsec); 411 struct timeval tv; 412 413 tv.tv_sec = ts.tv_sec; 414 tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000; 415 416 return tv; 417 } 418 EXPORT_SYMBOL(ns_to_timeval); 419 420 #if BITS_PER_LONG == 32 421 /** 422 * set_normalized_timespec - set timespec sec and nsec parts and normalize 423 * 424 * @ts: pointer to timespec variable to be set 425 * @sec: seconds to set 426 * @nsec: nanoseconds to set 427 * 428 * Set seconds and nanoseconds field of a timespec variable and 429 * normalize to the timespec storage format 430 * 431 * Note: The tv_nsec part is always in the range of 432 * 0 <= tv_nsec < NSEC_PER_SEC 433 * For negative values only the tv_sec field is negative ! 434 */ 435 void set_normalized_timespec64(struct timespec64 *ts, time64_t sec, s64 nsec) 436 { 437 while (nsec >= NSEC_PER_SEC) { 438 /* 439 * The following asm() prevents the compiler from 440 * optimising this loop into a modulo operation. See 441 * also __iter_div_u64_rem() in include/linux/time.h 442 */ 443 asm("" : "+rm"(nsec)); 444 nsec -= NSEC_PER_SEC; 445 ++sec; 446 } 447 while (nsec < 0) { 448 asm("" : "+rm"(nsec)); 449 nsec += NSEC_PER_SEC; 450 --sec; 451 } 452 ts->tv_sec = sec; 453 ts->tv_nsec = nsec; 454 } 455 EXPORT_SYMBOL(set_normalized_timespec64); 456 457 /** 458 * ns_to_timespec64 - Convert nanoseconds to timespec64 459 * @nsec: the nanoseconds value to be converted 460 * 461 * Returns the timespec64 representation of the nsec parameter. 462 */ 463 struct timespec64 ns_to_timespec64(const s64 nsec) 464 { 465 struct timespec64 ts; 466 s32 rem; 467 468 if (!nsec) 469 return (struct timespec64) {0, 0}; 470 471 ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem); 472 if (unlikely(rem < 0)) { 473 ts.tv_sec--; 474 rem += NSEC_PER_SEC; 475 } 476 ts.tv_nsec = rem; 477 478 return ts; 479 } 480 EXPORT_SYMBOL(ns_to_timespec64); 481 #endif 482 /* 483 * When we convert to jiffies then we interpret incoming values 484 * the following way: 485 * 486 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET) 487 * 488 * - 'too large' values [that would result in larger than 489 * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too. 490 * 491 * - all other values are converted to jiffies by either multiplying 492 * the input value by a factor or dividing it with a factor 493 * 494 * We must also be careful about 32-bit overflows. 495 */ 496 unsigned long msecs_to_jiffies(const unsigned int m) 497 { 498 /* 499 * Negative value, means infinite timeout: 500 */ 501 if ((int)m < 0) 502 return MAX_JIFFY_OFFSET; 503 504 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) 505 /* 506 * HZ is equal to or smaller than 1000, and 1000 is a nice 507 * round multiple of HZ, divide with the factor between them, 508 * but round upwards: 509 */ 510 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ); 511 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) 512 /* 513 * HZ is larger than 1000, and HZ is a nice round multiple of 514 * 1000 - simply multiply with the factor between them. 515 * 516 * But first make sure the multiplication result cannot 517 * overflow: 518 */ 519 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET)) 520 return MAX_JIFFY_OFFSET; 521 522 return m * (HZ / MSEC_PER_SEC); 523 #else 524 /* 525 * Generic case - multiply, round and divide. But first 526 * check that if we are doing a net multiplication, that 527 * we wouldn't overflow: 528 */ 529 if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET)) 530 return MAX_JIFFY_OFFSET; 531 532 return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32) 533 >> MSEC_TO_HZ_SHR32; 534 #endif 535 } 536 EXPORT_SYMBOL(msecs_to_jiffies); 537 538 unsigned long usecs_to_jiffies(const unsigned int u) 539 { 540 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET)) 541 return MAX_JIFFY_OFFSET; 542 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) 543 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ); 544 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) 545 return u * (HZ / USEC_PER_SEC); 546 #else 547 return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32) 548 >> USEC_TO_HZ_SHR32; 549 #endif 550 } 551 EXPORT_SYMBOL(usecs_to_jiffies); 552 553 /* 554 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note 555 * that a remainder subtract here would not do the right thing as the 556 * resolution values don't fall on second boundries. I.e. the line: 557 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding. 558 * Note that due to the small error in the multiplier here, this 559 * rounding is incorrect for sufficiently large values of tv_nsec, but 560 * well formed timespecs should have tv_nsec < NSEC_PER_SEC, so we're 561 * OK. 562 * 563 * Rather, we just shift the bits off the right. 564 * 565 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec 566 * value to a scaled second value. 567 */ 568 static unsigned long 569 __timespec_to_jiffies(unsigned long sec, long nsec) 570 { 571 nsec = nsec + TICK_NSEC - 1; 572 573 if (sec >= MAX_SEC_IN_JIFFIES){ 574 sec = MAX_SEC_IN_JIFFIES; 575 nsec = 0; 576 } 577 return (((u64)sec * SEC_CONVERSION) + 578 (((u64)nsec * NSEC_CONVERSION) >> 579 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; 580 581 } 582 583 unsigned long 584 timespec_to_jiffies(const struct timespec *value) 585 { 586 return __timespec_to_jiffies(value->tv_sec, value->tv_nsec); 587 } 588 589 EXPORT_SYMBOL(timespec_to_jiffies); 590 591 void 592 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value) 593 { 594 /* 595 * Convert jiffies to nanoseconds and separate with 596 * one divide. 597 */ 598 u32 rem; 599 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC, 600 NSEC_PER_SEC, &rem); 601 value->tv_nsec = rem; 602 } 603 EXPORT_SYMBOL(jiffies_to_timespec); 604 605 /* 606 * We could use a similar algorithm to timespec_to_jiffies (with a 607 * different multiplier for usec instead of nsec). But this has a 608 * problem with rounding: we can't exactly add TICK_NSEC - 1 to the 609 * usec value, since it's not necessarily integral. 610 * 611 * We could instead round in the intermediate scaled representation 612 * (i.e. in units of 1/2^(large scale) jiffies) but that's also 613 * perilous: the scaling introduces a small positive error, which 614 * combined with a division-rounding-upward (i.e. adding 2^(scale) - 1 615 * units to the intermediate before shifting) leads to accidental 616 * overflow and overestimates. 617 * 618 * At the cost of one additional multiplication by a constant, just 619 * use the timespec implementation. 620 */ 621 unsigned long 622 timeval_to_jiffies(const struct timeval *value) 623 { 624 return __timespec_to_jiffies(value->tv_sec, 625 value->tv_usec * NSEC_PER_USEC); 626 } 627 EXPORT_SYMBOL(timeval_to_jiffies); 628 629 void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value) 630 { 631 /* 632 * Convert jiffies to nanoseconds and separate with 633 * one divide. 634 */ 635 u32 rem; 636 637 value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC, 638 NSEC_PER_SEC, &rem); 639 value->tv_usec = rem / NSEC_PER_USEC; 640 } 641 EXPORT_SYMBOL(jiffies_to_timeval); 642 643 /* 644 * Convert jiffies/jiffies_64 to clock_t and back. 645 */ 646 clock_t jiffies_to_clock_t(unsigned long x) 647 { 648 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 649 # if HZ < USER_HZ 650 return x * (USER_HZ / HZ); 651 # else 652 return x / (HZ / USER_HZ); 653 # endif 654 #else 655 return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ); 656 #endif 657 } 658 EXPORT_SYMBOL(jiffies_to_clock_t); 659 660 unsigned long clock_t_to_jiffies(unsigned long x) 661 { 662 #if (HZ % USER_HZ)==0 663 if (x >= ~0UL / (HZ / USER_HZ)) 664 return ~0UL; 665 return x * (HZ / USER_HZ); 666 #else 667 /* Don't worry about loss of precision here .. */ 668 if (x >= ~0UL / HZ * USER_HZ) 669 return ~0UL; 670 671 /* .. but do try to contain it here */ 672 return div_u64((u64)x * HZ, USER_HZ); 673 #endif 674 } 675 EXPORT_SYMBOL(clock_t_to_jiffies); 676 677 u64 jiffies_64_to_clock_t(u64 x) 678 { 679 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 680 # if HZ < USER_HZ 681 x = div_u64(x * USER_HZ, HZ); 682 # elif HZ > USER_HZ 683 x = div_u64(x, HZ / USER_HZ); 684 # else 685 /* Nothing to do */ 686 # endif 687 #else 688 /* 689 * There are better ways that don't overflow early, 690 * but even this doesn't overflow in hundreds of years 691 * in 64 bits, so.. 692 */ 693 x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ)); 694 #endif 695 return x; 696 } 697 EXPORT_SYMBOL(jiffies_64_to_clock_t); 698 699 u64 nsec_to_clock_t(u64 x) 700 { 701 #if (NSEC_PER_SEC % USER_HZ) == 0 702 return div_u64(x, NSEC_PER_SEC / USER_HZ); 703 #elif (USER_HZ % 512) == 0 704 return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512); 705 #else 706 /* 707 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024, 708 * overflow after 64.99 years. 709 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ... 710 */ 711 return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ); 712 #endif 713 } 714 715 /** 716 * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64 717 * 718 * @n: nsecs in u64 719 * 720 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64. 721 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed 722 * for scheduler, not for use in device drivers to calculate timeout value. 723 * 724 * note: 725 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512) 726 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years 727 */ 728 u64 nsecs_to_jiffies64(u64 n) 729 { 730 #if (NSEC_PER_SEC % HZ) == 0 731 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */ 732 return div_u64(n, NSEC_PER_SEC / HZ); 733 #elif (HZ % 512) == 0 734 /* overflow after 292 years if HZ = 1024 */ 735 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512); 736 #else 737 /* 738 * Generic case - optimized for cases where HZ is a multiple of 3. 739 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc. 740 */ 741 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ); 742 #endif 743 } 744 EXPORT_SYMBOL(nsecs_to_jiffies64); 745 746 /** 747 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies 748 * 749 * @n: nsecs in u64 750 * 751 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64. 752 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed 753 * for scheduler, not for use in device drivers to calculate timeout value. 754 * 755 * note: 756 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512) 757 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years 758 */ 759 unsigned long nsecs_to_jiffies(u64 n) 760 { 761 return (unsigned long)nsecs_to_jiffies64(n); 762 } 763 EXPORT_SYMBOL_GPL(nsecs_to_jiffies); 764 765 /* 766 * Add two timespec values and do a safety check for overflow. 767 * It's assumed that both values are valid (>= 0) 768 */ 769 struct timespec timespec_add_safe(const struct timespec lhs, 770 const struct timespec rhs) 771 { 772 struct timespec res; 773 774 set_normalized_timespec(&res, lhs.tv_sec + rhs.tv_sec, 775 lhs.tv_nsec + rhs.tv_nsec); 776 777 if (res.tv_sec < lhs.tv_sec || res.tv_sec < rhs.tv_sec) 778 res.tv_sec = TIME_T_MAX; 779 780 return res; 781 } 782