4 * clock.c was written by Charles Hedrick, hedrick@cs.rutgers.edu, Apr 1992
5 * Modified for clock adjustments - Rob Hooft <hooft@chem.ruu.nl>, Nov 1992
6 * Improvements by Harald Koenig <koenig@nova.tat.physik.uni-tuebingen.de>
7 * and Alan Modra <alan@spri.levels.unisa.edu.au>.
9 * Major rewrite by Bryan Henderson <bryanh@giraffe-data.com>, 96.09.19.
10 * The new program is called hwclock. New features:
12 * - You can set the hardware clock without also modifying the system
14 * - You can read and set the clock with finer than 1 second precision.
15 * - When you set the clock, hwclock automatically refigures the drift
16 * rate, based on how far off the clock was before you set it.
18 * Reshuffled things, added sparc code, and re-added alpha stuff
19 * by David Mosberger <davidm@azstarnet.com>
20 * and Jay Estabrook <jestabro@amt.tay1.dec.com>
21 * and Martin Ostermann <ost@coments.rwth-aachen.de>, aeb@cwi.nl, 990212.
23 * Fix for Award 2094 bug, Dave Coffin (dcoffin@shore.net) 11/12/98
24 * Change of local time handling, Stefan Ring <e9725446@stud3.tuwien.ac.at>
25 * Change of adjtime handling, James P. Rutledge <ao112@rgfn.epcc.edu>.
27 * Distributed under GPL
30 * Explanation of `adjusting' (Rob Hooft):
32 * The problem with my machine is that its CMOS clock is 10 seconds
33 * per day slow. With this version of clock.c, and my '/etc/rc.local'
34 * reading '/etc/clock -au' instead of '/etc/clock -u -s', this error
35 * is automatically corrected at every boot.
37 * To do this job, the program reads and writes the file '/etc/adjtime'
38 * to determine the correction, and to save its data. In this file are
41 * 1) the correction in seconds per day. (So if your clock runs 5
42 * seconds per day fast, the first number should read -5.0)
43 * 2) the number of seconds since 1/1/1970 the last time the program
45 * 3) the remaining part of a second which was leftover after the last
48 * Installation and use of this program:
50 * a) create a file '/etc/adjtime' containing as the first and only
52 * b) run 'clock -au' or 'clock -a', depending on whether your cmos is
53 * in universal or local time. This updates the second number.
54 * c) set your system time using the 'date' command.
55 * d) update your cmos time using 'clock -wu' or 'clock -w'
56 * e) replace the first number in /etc/adjtime by your correction.
57 * f) put the command 'clock -au' or 'clock -a' in your '/etc/rc.local'
74 #define OPTUTILS_EXIT_CODE EX_USAGE
77 #include "closestream.h"
80 #include "pathnames.h"
83 #include "timeutils.h"
89 static int hwaudit_fd
= -1;
92 /* The struct that holds our hardware access routines */
93 static struct clock_ops
*ur
;
95 /* Maximal clock adjustment in seconds per day.
96 (adjtime() glibc call has 2145 seconds limit on i386, so it is good enough for us as well,
97 43219 is a maximal safe value preventing exact_adjustment overflow.) */
98 #define MAX_DRIFT 2145.0
102 * This is information we keep in the adjtime file that tells us how
103 * to do drift corrections. Elements are all straight from the
104 * adjtime file, so see documentation of that file for details.
105 * Exception is <dirty>, which is an indication that what's in this
106 * structure is not what's in the disk file (because it has been
107 * updated since read from the disk file).
112 time_t last_adj_time
;
115 time_t last_calib_time
;
117 * The most recent time that we set the clock from an external
118 * authority (as opposed to just doing a drift adjustment)
121 enum a_local_utc
{ UTC
= 0, LOCAL
, UNKNOWN
} local_utc
;
123 * To which time zone, local or UTC, we most recently set the
129 * time_t to timeval conversion.
131 static struct timeval
t2tv(time_t timet
)
133 struct timeval rettimeval
;
135 rettimeval
.tv_sec
= timet
;
136 rettimeval
.tv_usec
= 0;
141 * The difference in seconds between two times in "timeval" format.
143 double time_diff(struct timeval subtrahend
, struct timeval subtractor
)
145 return (subtrahend
.tv_sec
- subtractor
.tv_sec
)
146 + (subtrahend
.tv_usec
- subtractor
.tv_usec
) / 1E6
;
150 * The time, in "timeval" format, which is <increment> seconds after the
151 * time <addend>. Of course, <increment> may be negative.
153 static struct timeval
time_inc(struct timeval addend
, double increment
)
155 struct timeval newtime
;
157 newtime
.tv_sec
= addend
.tv_sec
+ (int)increment
;
158 newtime
.tv_usec
= addend
.tv_usec
+ (increment
- (int)increment
) * 1E6
;
161 * Now adjust it so that the microsecond value is between 0 and 1
164 if (newtime
.tv_usec
< 0) {
165 newtime
.tv_usec
+= 1E6
;
167 } else if (newtime
.tv_usec
>= 1E6
) {
168 newtime
.tv_usec
-= 1E6
;
175 hw_clock_is_utc(const struct hwclock_control
*ctl
,
176 const struct adjtime adjtime
)
181 ret
= TRUE
; /* --utc explicitly given on command line */
182 else if (ctl
->local_opt
)
183 ret
= FALSE
; /* --localtime explicitly given */
185 /* get info from adjtime file - default is UTC */
186 ret
= (adjtime
.local_utc
!= LOCAL
);
188 printf(_("Assuming hardware clock is kept in %s time.\n"),
189 ret
? _("UTC") : _("local"));
194 * Read the adjustment parameters out of the /etc/adjtime file.
196 * Return them as the adjtime structure <*adjtime_p>. If there is no
197 * /etc/adjtime file, return defaults. If values are missing from the file,
198 * return defaults for them.
200 * return value 0 if all OK, !=0 otherwise.
202 static int read_adjtime(const struct hwclock_control
*ctl
,
203 struct adjtime
*adjtime_p
)
206 char line1
[81]; /* String: first line of adjtime file */
207 char line2
[81]; /* String: second line of adjtime file */
208 char line3
[81]; /* String: third line of adjtime file */
210 if (access(ctl
->adj_file_name
, R_OK
) != 0)
213 adjfile
= fopen(ctl
->adj_file_name
, "r"); /* open file for reading */
214 if (adjfile
== NULL
) {
215 warn(_("cannot open %s"), ctl
->adj_file_name
);
219 if (!fgets(line1
, sizeof(line1
), adjfile
))
220 line1
[0] = '\0'; /* In case fgets fails */
221 if (!fgets(line2
, sizeof(line2
), adjfile
))
222 line2
[0] = '\0'; /* In case fgets fails */
223 if (!fgets(line3
, sizeof(line3
), adjfile
))
224 line3
[0] = '\0'; /* In case fgets fails */
228 sscanf(line1
, "%lf %ld %lf",
229 &adjtime_p
->drift_factor
,
230 &adjtime_p
->last_adj_time
,
231 &adjtime_p
->not_adjusted
);
233 sscanf(line2
, "%ld", &adjtime_p
->last_calib_time
);
235 if (!strcmp(line3
, "UTC\n")) {
236 adjtime_p
->local_utc
= UTC
;
237 } else if (!strcmp(line3
, "LOCAL\n")) {
238 adjtime_p
->local_utc
= LOCAL
;
240 adjtime_p
->local_utc
= UNKNOWN
;
242 warnx(_("Warning: unrecognized third line in adjtime file\n"
243 "(Expected: `UTC' or `LOCAL' or nothing.)"));
249 ("Last drift adjustment done at %ld seconds after 1969\n"),
250 (long)adjtime_p
->last_adj_time
);
251 printf(_("Last calibration done at %ld seconds after 1969\n"),
252 (long)adjtime_p
->last_calib_time
);
253 printf(_("Hardware clock is on %s time\n"),
254 (adjtime_p
->local_utc
==
255 LOCAL
) ? _("local") : (adjtime_p
->local_utc
==
256 UTC
) ? _("UTC") : _("unknown"));
263 * Wait until the falling edge of the Hardware Clock's update flag so that
264 * any time that is read from the clock immediately after we return will be
267 * The clock only has 1 second precision, so it gives the exact time only
268 * once per second, right on the falling edge of the update flag.
270 * We wait (up to one second) either blocked waiting for an rtc device or in
271 * a CPU spin loop. The former is probably not very accurate.
273 * Return 0 if it worked, nonzero if it didn't.
275 static int synchronize_to_clock_tick(const struct hwclock_control
*ctl
)
280 printf(_("Waiting for clock tick...\n"));
282 rc
= ur
->synchronize_to_clock_tick(ctl
);
286 printf(_("...synchronization failed\n"));
288 printf(_("...got clock tick\n"));
295 * Convert a time in broken down format (hours, minutes, etc.) into standard
296 * unix time (seconds into epoch). Return it as *systime_p.
298 * The broken down time is argument <tm>. This broken down time is either
299 * in local time zone or UTC, depending on value of logical argument
300 * "universal". True means it is in UTC.
302 * If the argument contains values that do not constitute a valid time, and
303 * mktime() recognizes this, return *valid_p == false and *systime_p
304 * undefined. However, mktime() sometimes goes ahead and computes a
305 * fictional time "as if" the input values were valid, e.g. if they indicate
306 * the 31st day of April, mktime() may compute the time of May 1. In such a
307 * case, we return the same fictional value mktime() does as *systime_p and
308 * return *valid_p == true.
311 mktime_tz(const struct hwclock_control
*ctl
, struct tm tm
,
312 bool *valid_p
, time_t *systime_p
)
315 *systime_p
= timegm(&tm
);
317 *systime_p
= mktime(&tm
);
318 if (*systime_p
== -1) {
320 * This apparently (not specified in mktime() documentation)
321 * means the 'tm' structure does not contain valid values
322 * (however, not containing valid values does _not_ imply
323 * mktime() returns -1).
327 printf(_("Invalid values in hardware clock: "
328 "%4d/%.2d/%.2d %.2d:%.2d:%.2d\n"),
329 tm
.tm_year
+ 1900, tm
.tm_mon
+ 1, tm
.tm_mday
,
330 tm
.tm_hour
, tm
.tm_min
, tm
.tm_sec
);
335 ("Hw clock time : %4d/%.2d/%.2d %.2d:%.2d:%.2d = "
336 "%ld seconds since 1969\n"), tm
.tm_year
+ 1900,
337 tm
.tm_mon
+ 1, tm
.tm_mday
, tm
.tm_hour
, tm
.tm_min
,
338 tm
.tm_sec
, (long)*systime_p
);
343 * Read the hardware clock and return the current time via <tm> argument.
345 * Use the method indicated by <method> argument to access the hardware
349 read_hardware_clock(const struct hwclock_control
*ctl
,
350 bool * valid_p
, time_t *systime_p
)
355 err
= ur
->read_hardware_clock(ctl
, &tm
);
361 ("Time read from Hardware Clock: %4d/%.2d/%.2d %02d:%02d:%02d\n"),
362 tm
.tm_year
+ 1900, tm
.tm_mon
+ 1, tm
.tm_mday
, tm
.tm_hour
,
363 tm
.tm_min
, tm
.tm_sec
);
364 mktime_tz(ctl
, tm
, valid_p
, systime_p
);
370 * Set the Hardware Clock to the time <newtime>, in local time zone or UTC,
371 * according to <universal>.
374 set_hardware_clock(const struct hwclock_control
*ctl
, const time_t newtime
)
376 struct tm new_broken_time
;
378 * Time to which we will set Hardware Clock, in broken down format,
379 * in the time zone of caller's choice
383 new_broken_time
= *gmtime(&newtime
);
385 new_broken_time
= *localtime(&newtime
);
388 printf(_("Setting Hardware Clock to %.2d:%.2d:%.2d "
389 "= %ld seconds since 1969\n"),
390 new_broken_time
.tm_hour
, new_broken_time
.tm_min
,
391 new_broken_time
.tm_sec
, (long)newtime
);
394 printf(_("Clock not changed - testing only.\n"));
396 ur
->set_hardware_clock(ctl
, &new_broken_time
);
401 * Set the Hardware Clock to the time "sethwtime", in local time zone or
402 * UTC, according to "universal".
404 * Wait for a fraction of a second so that "sethwtime" is the value of the
405 * Hardware Clock as of system time "refsystime", which is in the past. For
406 * example, if "sethwtime" is 14:03:05 and "refsystime" is 12:10:04.5 and
407 * the current system time is 12:10:06.0: Wait .5 seconds (to make exactly 2
408 * seconds since "refsystime") and then set the Hardware Clock to 14:03:07,
409 * thus getting a precise and retroactive setting of the clock.
411 * (Don't be confused by the fact that the system clock and the Hardware
412 * Clock differ by two hours in the above example. That's just to remind you
413 * that there are two independent time scales here).
415 * This function ought to be able to accept set times as fractional times.
416 * Idea for future enhancement.
419 set_hardware_clock_exact(const struct hwclock_control
*ctl
,
420 const time_t sethwtime
,
421 const struct timeval refsystime
)
424 * The Hardware Clock can only be set to any integer time plus one
425 * half second. The integer time is required because there is no
426 * interface to set or get a fractional second. The additional half
427 * second is because the Hardware Clock updates to the following
428 * second precisely 500 ms (not 1 second!) after you release the
429 * divider reset (after setting the new time) - see description of
430 * DV2, DV1, DV0 in Register A in the MC146818A data sheet (and note
431 * that although that document doesn't say so, real-world code seems
432 * to expect that the SET bit in Register B functions the same way).
433 * That means that, e.g., when you set the clock to 1:02:03, it
434 * effectively really sets it to 1:02:03.5, because it will update to
435 * 1:02:04 only half a second later. Our caller passes the desired
436 * integer Hardware Clock time in sethwtime, and the corresponding
437 * system time (which may have a fractional part, and which may or may
438 * not be the same!) in refsystime. In an ideal situation, we would
439 * then apply sethwtime to the Hardware Clock at refsystime+500ms, so
440 * that when the Hardware Clock ticks forward to sethwtime+1s half a
441 * second later at refsystime+1000ms, everything is in sync. So we
442 * spin, waiting for gettimeofday() to return a time at or after that
443 * time (refsystime+500ms) up to a tolerance value, initially 1ms. If
444 * we miss that time due to being preempted for some other process,
445 * then we increase the margin a little bit (initially 1ms, doubling
446 * each time), add 1 second (or more, if needed to get a time that is
447 * in the future) to both the time for which we are waiting and the
448 * time that we will apply to the Hardware Clock, and start waiting
451 * For example, the caller requests that we set the Hardware Clock to
452 * 1:02:03, with reference time (current system time) = 6:07:08.250.
453 * We want the Hardware Clock to update to 1:02:04 at 6:07:09.250 on
454 * the system clock, and the first such update will occur 0.500
455 * seconds after we write to the Hardware Clock, so we spin until the
456 * system clock reads 6:07:08.750. If we get there, great, but let's
457 * imagine the system is so heavily loaded that our process is
458 * preempted and by the time we get to run again, the system clock
459 * reads 6:07:11.990. We now want to wait until the next xx:xx:xx.750
460 * time, which is 6:07:12.750 (4.5 seconds after the reference time),
461 * at which point we will set the Hardware Clock to 1:02:07 (4 seconds
462 * after the originally requested time). If we do that successfully,
463 * then at 6:07:13.250 (5 seconds after the reference time), the
464 * Hardware Clock will update to 1:02:08 (5 seconds after the
465 * originally requested time), and all is well thereafter.
468 time_t newhwtime
= sethwtime
;
469 double target_time_tolerance_secs
= 0.001; /* initial value */
470 double tolerance_incr_secs
= 0.001; /* initial value */
471 const double RTC_SET_DELAY_SECS
= 0.5; /* 500 ms */
472 const struct timeval RTC_SET_DELAY_TV
= { 0, RTC_SET_DELAY_SECS
* 1E6
};
474 struct timeval targetsystime
;
475 struct timeval nowsystime
;
476 struct timeval prevsystime
= refsystime
;
477 double deltavstarget
;
479 timeradd(&refsystime
, &RTC_SET_DELAY_TV
, &targetsystime
);
484 /* FOR TESTING ONLY: inject random delays of up to 1000ms */
485 if (ctl
->debug
>= 10) {
486 int usec
= random() % 1000000;
487 printf(_("sleeping ~%d usec\n"), usec
);
491 gettimeofday(&nowsystime
, NULL
);
492 deltavstarget
= time_diff(nowsystime
, targetsystime
);
493 ticksize
= time_diff(nowsystime
, prevsystime
);
494 prevsystime
= nowsystime
;
498 printf(_("time jumped backward %.6f seconds "
499 "to %ld.%06ld - retargeting\n"),
500 ticksize
, nowsystime
.tv_sec
,
502 /* The retarget is handled at the end of the loop. */
503 } else if (deltavstarget
< 0) {
504 /* deltavstarget < 0 if current time < target time */
506 printf(_("%ld.%06ld < %ld.%06ld (%.6f)\n"),
509 targetsystime
.tv_sec
,
510 targetsystime
.tv_usec
,
512 continue; /* not there yet - keep spinning */
513 } else if (deltavstarget
<= target_time_tolerance_secs
) {
514 /* Close enough to the target time; done waiting. */
516 } else /* (deltavstarget > target_time_tolerance_secs) */ {
518 * We missed our window. Increase the tolerance and
519 * aim for the next opportunity.
522 printf(_("missed it - %ld.%06ld is too far "
523 "past %ld.%06ld (%.6f > %.6f)\n"),
526 targetsystime
.tv_sec
,
527 targetsystime
.tv_usec
,
529 target_time_tolerance_secs
);
530 target_time_tolerance_secs
+= tolerance_incr_secs
;
531 tolerance_incr_secs
*= 2;
535 * Aim for the same offset (tv_usec) within the second in
536 * either the current second (if that offset hasn't arrived
537 * yet), or the next second.
539 if (nowsystime
.tv_usec
< targetsystime
.tv_usec
)
540 targetsystime
.tv_sec
= nowsystime
.tv_sec
;
542 targetsystime
.tv_sec
= nowsystime
.tv_sec
+ 1;
545 newhwtime
= sethwtime
546 + (int)(time_diff(nowsystime
, refsystime
)
547 - RTC_SET_DELAY_SECS
/* don't count this */
548 + 0.5 /* for rounding */);
550 printf(_("%ld.%06ld is close enough to %ld.%06ld (%.6f < %.6f)\n"
551 "Set RTC to %ld (%ld + %d; refsystime = %ld.%06ld)\n"),
552 nowsystime
.tv_sec
, nowsystime
.tv_usec
,
553 targetsystime
.tv_sec
, targetsystime
.tv_usec
,
554 deltavstarget
, target_time_tolerance_secs
,
555 newhwtime
, sethwtime
,
556 (int)(newhwtime
- sethwtime
),
557 refsystime
.tv_sec
, refsystime
.tv_usec
);
559 set_hardware_clock(ctl
, newhwtime
);
563 * Put the time "hwctime" on standard output in display format. Except if
564 * hclock_valid == false, just tell standard output that we don't know what
568 display_time(const bool hclock_valid
, struct timeval hwctime
)
572 ("The Hardware Clock registers contain values that are "
573 "either invalid (e.g. 50th day of month) or beyond the range "
574 "we can handle (e.g. Year 2095)."));
576 char buf
[ISO_8601_BUFSIZ
];
578 strtimeval_iso(&hwctime
, ISO_8601_DATE
|ISO_8601_TIME
|ISO_8601_DOTUSEC
|
579 ISO_8601_TIMEZONE
|ISO_8601_SPACE
,
586 * Set the System Clock to time 'newtime'.
588 * Also set the kernel time zone value to the value indicated by the TZ
589 * environment variable and/or /usr/lib/zoneinfo/, interpreted as tzset()
590 * would interpret them.
592 * If this is the first call of settimeofday since boot, then this also sets
593 * the kernel variable persistent_clock_is_local so that NTP 11 minute mode
594 * will update the Hardware Clock with the proper timescale. If the Hardware
595 * Clock's timescale configuration is changed then a reboot is required for
596 * persistent_clock_is_local to be updated.
598 * EXCEPT: if hclock_valid is false, just issue an error message saying
599 * there is no valid time in the Hardware Clock to which to set the system
602 * If 'testing' is true, don't actually update anything -- just say we would
606 set_system_clock(const struct hwclock_control
*ctl
, const bool hclock_valid
,
607 const struct timeval newtime
)
613 ("The Hardware Clock does not contain a valid time, so "
614 "we cannot set the System Time from it."));
617 const struct timeval
*tv_null
= NULL
;
622 broken
= localtime(&newtime
.tv_sec
);
623 #ifdef HAVE_TM_GMTOFF
624 minuteswest
= -broken
->tm_gmtoff
/ 60; /* GNU extension */
626 minuteswest
= timezone
/ 60;
627 if (broken
->tm_isdst
)
632 printf(_("Calling settimeofday:\n"));
633 printf(_("\ttv.tv_sec = %ld, tv.tv_usec = %ld\n"),
634 newtime
.tv_sec
, newtime
.tv_usec
);
635 printf(_("\ttz.tz_minuteswest = %d\n"), minuteswest
);
639 ("Not setting system clock because running in test mode.\n"));
642 const struct timezone tz
= { minuteswest
, 0 };
644 /* Set kernel persistent_clock_is_local so that 11 minute
645 * mode does not clobber the Hardware Clock with UTC. This
646 * is only available on first call of settimeofday after boot.
649 rc
= settimeofday(tv_null
, &tz
);
651 rc
= settimeofday(&newtime
, &tz
);
653 if (errno
== EPERM
) {
655 ("Must be superuser to set system clock."));
658 warn(_("settimeofday() failed"));
669 * Reset the System Clock from local time to UTC, based on its current value
670 * and the timezone unless universal is TRUE.
672 * Also set the kernel time zone value to the value indicated by the TZ
673 * environment variable and/or /usr/lib/zoneinfo/, interpreted as tzset()
674 * would interpret them.
676 * If 'testing' is true, don't actually update anything -- just say we would
679 static int set_system_clock_timezone(const struct hwclock_control
*ctl
)
686 gettimeofday(&tv
, NULL
);
688 struct tm broken_time
;
691 broken_time
= *gmtime(&tv
.tv_sec
);
692 strftime(ctime_now
, sizeof(ctime_now
), "%Y/%m/%d %H:%M:%S",
694 printf(_("Current system time: %ld = %s\n"), tv
.tv_sec
,
698 broken
= localtime(&tv
.tv_sec
);
699 #ifdef HAVE_TM_GMTOFF
700 minuteswest
= -broken
->tm_gmtoff
/ 60; /* GNU extension */
702 minuteswest
= timezone
/ 60;
703 if (broken
->tm_isdst
)
708 struct tm broken_time
;
711 gettimeofday(&tv
, NULL
);
713 tv
.tv_sec
+= minuteswest
* 60;
715 broken_time
= *gmtime(&tv
.tv_sec
);
716 strftime(ctime_now
, sizeof(ctime_now
), "%Y/%m/%d %H:%M:%S",
719 printf(_("Calling settimeofday:\n"));
720 printf(_("\tUTC: %s\n"), ctime_now
);
721 printf(_("\ttv.tv_sec = %ld, tv.tv_usec = %ld\n"),
722 tv
.tv_sec
, tv
.tv_usec
);
723 printf(_("\ttz.tz_minuteswest = %d\n"), minuteswest
);
727 ("Not setting system clock because running in test mode.\n"));
730 const struct timezone tz_utc
= { 0, 0 };
731 const struct timezone tz
= { minuteswest
, 0 };
732 const struct timeval
*tv_null
= NULL
;
735 /* The first call to settimeofday after boot will assume the systemtime
736 * is in localtime, and adjust it according to the given timezone to
737 * compensate. If the systemtime is in fact in UTC, then this is wrong
738 * so we first do a dummy call to make sure the time is not shifted.
741 rc
= settimeofday(tv_null
, &tz_utc
);
743 /* Now we set the real timezone. Due to the above dummy call, this will
744 * only warp the systemtime if the RTC is not in UTC. */
746 rc
= settimeofday(tv_null
, &tz
);
749 if (errno
== EPERM
) {
751 ("Must be superuser to set system clock."));
754 warn(_("settimeofday() failed"));
764 * Refresh the last calibrated and last adjusted timestamps in <*adjtime_p>
765 * to facilitate future drift calculations based on this set point.
767 * With the --update-drift option:
768 * Update the drift factor in <*adjtime_p> based on the fact that the
769 * Hardware Clock was just calibrated to <nowtime> and before that was
770 * set to the <hclocktime> time scale.
772 * EXCEPT: if <hclock_valid> is false, assume Hardware Clock was not set
773 * before to anything meaningful and regular adjustments have not been done,
774 * so don't adjust the drift factor.
777 adjust_drift_factor(const struct hwclock_control
*ctl
,
778 struct adjtime
*adjtime_p
,
779 const struct timeval nowtime
,
780 const bool hclock_valid
,
781 const struct timeval hclocktime
)
785 printf(_("Not adjusting drift factor because the "
786 "--update-drift option was not used.\n"));
787 } else if (!hclock_valid
) {
789 printf(_("Not adjusting drift factor because the "
790 "Hardware Clock previously contained "
792 } else if (adjtime_p
->last_calib_time
== 0) {
794 printf(_("Not adjusting drift factor because last "
795 "calibration time is zero,\n"
796 "so history is bad and calibration startover "
798 } else if ((hclocktime
.tv_sec
- adjtime_p
->last_calib_time
) < 4 * 60 * 60) {
800 printf(_("Not adjusting drift factor because it has "
801 "been less than four hours since the last "
805 * At adjustment time we drift correct the hardware clock
806 * according to the contents of the adjtime file and refresh
807 * its last adjusted timestamp.
809 * At calibration time we set the Hardware Clock and refresh
810 * both timestamps in <*adjtime_p>.
812 * Here, with the --update-drift option, we also update the
813 * drift factor in <*adjtime_p>.
815 * Let us do computation in doubles. (Floats almost suffice,
816 * but 195 days + 1 second equals 195 days in floats.)
818 const double sec_per_day
= 24.0 * 60.0 * 60.0;
819 double factor_adjust
;
821 struct timeval last_calib
;
823 last_calib
= t2tv(adjtime_p
->last_calib_time
);
825 * Correction to apply to the current drift factor.
827 * Simplified: uncorrected_drift / days_since_calibration.
829 * hclocktime is fully corrected with the current drift factor.
830 * Its difference from nowtime is the missed drift correction.
832 factor_adjust
= time_diff(nowtime
, hclocktime
) /
833 (time_diff(nowtime
, last_calib
) / sec_per_day
);
835 drift_factor
= adjtime_p
->drift_factor
+ factor_adjust
;
836 if (fabs(drift_factor
) > MAX_DRIFT
) {
838 printf(_("Clock drift factor was calculated as "
840 "It is far too much. Resetting to zero.\n"),
845 printf(_("Clock drifted %f seconds in the past "
846 "%f seconds\nin spite of a drift factor of "
848 "Adjusting drift factor by %f seconds/day\n"),
849 time_diff(nowtime
, hclocktime
),
850 time_diff(nowtime
, last_calib
),
851 adjtime_p
->drift_factor
, factor_adjust
);
854 adjtime_p
->drift_factor
= drift_factor
;
856 adjtime_p
->last_calib_time
= nowtime
.tv_sec
;
858 adjtime_p
->last_adj_time
= nowtime
.tv_sec
;
860 adjtime_p
->not_adjusted
= 0;
862 adjtime_p
->dirty
= TRUE
;
866 * Calculate the drift correction currently needed for the
867 * Hardware Clock based on the last time it was adjusted,
868 * and the current drift factor, as stored in the adjtime file.
870 * The total drift adjustment needed is stored at tdrift_p.
874 calculate_adjustment(const struct hwclock_control
*ctl
,
876 const time_t last_time
,
877 const double not_adjusted
,
878 const time_t systime
, struct timeval
*tdrift_p
)
880 double exact_adjustment
;
883 ((double)(systime
- last_time
)) * factor
/ (24 * 60 * 60)
885 tdrift_p
->tv_sec
= (time_t) floor(exact_adjustment
);
886 tdrift_p
->tv_usec
= (exact_adjustment
-
887 (double)tdrift_p
->tv_sec
) * 1E6
;
889 printf(P_("Time since last adjustment is %ld second\n",
890 "Time since last adjustment is %ld seconds\n",
891 (systime
- last_time
)),
892 (systime
- last_time
));
893 printf(_("Calculated Hardware Clock drift is %ld.%06ld seconds\n"),
894 tdrift_p
->tv_sec
, tdrift_p
->tv_usec
);
899 * Write the contents of the <adjtime> structure to its disk file.
901 * But if the contents are clean (unchanged since read from disk), don't
904 static void save_adjtime(const struct hwclock_control
*ctl
,
905 const struct adjtime
*adjtime
)
907 char *content
; /* Stuff to write to disk file */
914 xasprintf(&content
, "%f %ld %f\n%ld\n%s\n",
915 adjtime
->drift_factor
,
916 adjtime
->last_adj_time
,
917 adjtime
->not_adjusted
,
918 adjtime
->last_calib_time
,
919 (adjtime
->local_utc
== LOCAL
) ? "LOCAL" : "UTC");
923 ("Not updating adjtime file because of testing mode.\n"));
924 printf(_("Would have written the following to %s:\n%s"),
925 ctl
->adj_file_name
, content
);
930 fp
= fopen(ctl
->adj_file_name
, "w");
932 warn(_("Could not open file with the clock adjustment parameters "
933 "in it (%s) for writing"), ctl
->adj_file_name
);
935 } else if (fputs(content
, fp
) < 0 || close_stream(fp
) != 0) {
936 warn(_("Could not update file with the clock adjustment "
937 "parameters (%s) in it"), ctl
->adj_file_name
);
942 warnx(_("Drift adjustment parameters not updated."));
946 * Do the adjustment requested, by 1) setting the Hardware Clock (if
947 * necessary), and 2) updating the last-adjusted time in the adjtime
950 * Do not update anything if the Hardware Clock does not currently present a
953 * <hclock_valid> means the Hardware Clock contains a valid time.
955 * <hclocktime> is the drift corrected time read from the Hardware Clock.
957 * <read_time> was the system time when the <hclocktime> was read, which due
958 * to computational delay could be a short time ago. It is used to define a
959 * trigger point for setting the Hardware Clock. The fractional part of the
960 * Hardware clock set time is subtracted from read_time to 'refer back', or
961 * delay, the trigger point. Fractional parts must be accounted for in this
962 * way, because the Hardware Clock can only be set to a whole second.
964 * <universal>: the Hardware Clock is kept in UTC.
966 * <testing>: We are running in test mode (no updating of clock).
970 do_adjustment(const struct hwclock_control
*ctl
, struct adjtime
*adjtime_p
,
971 const bool hclock_valid
, const struct timeval hclocktime
,
972 const struct timeval read_time
)
975 warnx(_("The Hardware Clock does not contain a valid time, "
976 "so we cannot adjust it."));
977 adjtime_p
->last_calib_time
= 0; /* calibration startover is required */
978 adjtime_p
->last_adj_time
= 0;
979 adjtime_p
->not_adjusted
= 0;
980 adjtime_p
->dirty
= TRUE
;
981 } else if (adjtime_p
->last_adj_time
== 0) {
983 printf(_("Not setting clock because last adjustment time is zero, "
984 "so history is bad.\n"));
985 } else if (fabs(adjtime_p
->drift_factor
) > MAX_DRIFT
) {
987 printf(_("Not setting clock because drift factor %f is far too high.\n"),
988 adjtime_p
->drift_factor
);
990 set_hardware_clock_exact(ctl
, hclocktime
.tv_sec
,
992 -(hclocktime
.tv_usec
/ 1E6
)));
993 adjtime_p
->last_adj_time
= hclocktime
.tv_sec
;
994 adjtime_p
->not_adjusted
= 0;
995 adjtime_p
->dirty
= TRUE
;
999 static void determine_clock_access_method(const struct hwclock_control
*ctl
)
1004 ur
= probe_for_cmos_clock();
1007 ur
= probe_for_rtc_clock(ctl
);
1011 puts(ur
->interface_name
);
1015 printf(_("No usable clock interface found.\n"));
1016 warnx(_("Cannot access the Hardware Clock via "
1017 "any known method."));
1019 warnx(_("Use the --debug option to see the "
1020 "details of our search for an access "
1022 hwclock_exit(ctl
, EX_SOFTWARE
);
1027 * Do all the normal work of hwclock - read, set clock, etc.
1029 * Issue output to stdout and error message to stderr where appropriate.
1031 * Return rc == 0 if everything went OK, rc != 0 if not.
1034 manipulate_clock(const struct hwclock_control
*ctl
, const time_t set_time
,
1035 const struct timeval startup_time
, struct adjtime
*adjtime
)
1037 /* The time at which we read the Hardware Clock */
1038 struct timeval read_time
;
1040 * The Hardware Clock gives us a valid time, or at
1041 * least something close enough to fool mktime().
1043 bool hclock_valid
= FALSE
;
1045 * Tick synchronized time read from the Hardware Clock and
1046 * then drift correct for all operations except --show.
1048 struct timeval hclocktime
= { 0, 0 };
1049 /* Total Hardware Clock drift correction needed. */
1050 struct timeval tdrift
;
1051 /* local return code */
1054 if (!ctl
->systz
&& !ctl
->predict
&& ur
->get_permissions())
1057 if ((ctl
->set
|| ctl
->systohc
|| ctl
->adjust
) &&
1058 (adjtime
->local_utc
== UTC
) != ctl
->universal
) {
1059 adjtime
->local_utc
= ctl
->universal
? UTC
: LOCAL
;
1060 adjtime
->dirty
= TRUE
;
1063 if (ctl
->show
|| ctl
->get
|| ctl
->adjust
|| ctl
->hctosys
1064 || (!ctl
->noadjfile
&& !ctl
->systz
&& !ctl
->predict
)) {
1065 /* data from HW-clock are required */
1066 rc
= synchronize_to_clock_tick(ctl
);
1069 * We don't error out if the user is attempting to set the
1070 * RTC and synchronization timeout happens - the RTC could
1071 * be functioning but contain invalid time data so we still
1072 * want to allow a user to set the RTC time.
1074 if (rc
== RTC_BUSYWAIT_FAILED
&& !ctl
->set
&& !ctl
->systohc
)
1076 gettimeofday(&read_time
, NULL
);
1079 * If we can't synchronize to a clock tick,
1080 * we likely can't read from the RTC so
1081 * don't bother reading it again.
1084 rc
= read_hardware_clock(ctl
, &hclock_valid
,
1085 &hclocktime
.tv_sec
);
1086 if (rc
&& !ctl
->set
&& !ctl
->systohc
)
1091 * Calculate Hardware Clock drift for --predict with the user
1092 * supplied --date option time, and with the time read from the
1093 * Hardware Clock for all other operations. Apply drift correction
1094 * to the Hardware Clock time for everything except --show and
1095 * --predict. For --predict negate the drift correction, because we
1096 * want to 'predict' a future Hardware Clock time that includes drift.
1098 hclocktime
= ctl
->predict
? t2tv(set_time
) : hclocktime
;
1099 calculate_adjustment(ctl
, adjtime
->drift_factor
,
1100 adjtime
->last_adj_time
,
1101 adjtime
->not_adjusted
,
1102 hclocktime
.tv_sec
, &tdrift
);
1103 if (!ctl
->show
&& !ctl
->predict
)
1104 hclocktime
= time_inc(tdrift
, hclocktime
.tv_sec
);
1105 if (ctl
->show
|| ctl
->get
) {
1106 display_time(hclock_valid
,
1107 time_inc(hclocktime
, -time_diff
1108 (read_time
, startup_time
)));
1109 } else if (ctl
->set
) {
1110 set_hardware_clock_exact(ctl
, set_time
, startup_time
);
1111 if (!ctl
->noadjfile
)
1112 adjust_drift_factor(ctl
, adjtime
,
1113 time_inc(t2tv(set_time
), time_diff
1114 (read_time
, startup_time
)),
1115 hclock_valid
, hclocktime
);
1116 } else if (ctl
->adjust
) {
1117 if (tdrift
.tv_sec
> 0 || tdrift
.tv_sec
< -1)
1118 do_adjustment(ctl
, adjtime
, hclock_valid
,
1119 hclocktime
, read_time
);
1121 printf(_("Needed adjustment is less than one second, "
1122 "so not setting clock.\n"));
1123 } else if (ctl
->systohc
) {
1124 struct timeval nowtime
, reftime
;
1126 * We can only set_hardware_clock_exact to a
1127 * whole seconds time, so we set it with
1128 * reference to the most recent whole
1131 gettimeofday(&nowtime
, NULL
);
1132 reftime
.tv_sec
= nowtime
.tv_sec
;
1133 reftime
.tv_usec
= 0;
1134 set_hardware_clock_exact(ctl
, (time_t) reftime
.tv_sec
, reftime
);
1135 if (!ctl
->noadjfile
)
1136 adjust_drift_factor(ctl
, adjtime
, nowtime
,
1137 hclock_valid
, hclocktime
);
1138 } else if (ctl
->hctosys
) {
1139 rc
= set_system_clock(ctl
, hclock_valid
, hclocktime
);
1141 printf(_("Unable to set system clock.\n"));
1144 } else if (ctl
->systz
) {
1145 rc
= set_system_clock_timezone(ctl
);
1147 printf(_("Unable to set system clock.\n"));
1150 } else if (ctl
->predict
) {
1151 hclocktime
= time_inc(hclocktime
, (double)
1152 -(tdrift
.tv_sec
+ tdrift
.tv_usec
/ 1E6
));
1155 ("At %ld seconds after 1969, RTC is predicted to read %ld seconds after 1969.\n"),
1156 set_time
, hclocktime
.tv_sec
);
1158 display_time(TRUE
, hclocktime
);
1160 if (!ctl
->noadjfile
)
1161 save_adjtime(ctl
, adjtime
);
1166 * Get or set the Hardware Clock epoch value in the kernel, as appropriate.
1167 * <getepoch>, <setepoch>, and <epoch> are hwclock invocation options.
1169 * <epoch> == -1 if the user did not specify an "epoch" option.
1173 * Maintenance note: This should work on non-Alpha machines, but the
1174 * evidence today (98.03.04) indicates that the kernel only keeps the epoch
1175 * value on Alphas. If that is ever fixed, this function should be changed.
1179 manipulate_epoch(const struct hwclock_control
*ctl
__attribute__((__unused__
)))
1181 warnx(_("The kernel keeps an epoch value for the Hardware Clock "
1182 "only on an Alpha machine.\nThis copy of hwclock was built for "
1183 "a machine other than Alpha\n(and thus is presumably not running "
1184 "on an Alpha now). No action taken."));
1188 manipulate_epoch(const struct hwclock_control
*ctl
)
1190 if (ctl
->getepoch
) {
1191 unsigned long epoch
;
1193 if (get_epoch_rtc(ctl
, &epoch
, 0))
1195 ("Unable to get the epoch value from the kernel."));
1197 printf(_("Kernel is assuming an epoch value of %lu\n"),
1199 } else if (ctl
->setepoch
) {
1200 if (ctl
->epoch_option
== 0)
1202 ("To set the epoch value, you must use the 'epoch' "
1203 "option to tell to what value to set it."));
1204 else if (ctl
->testing
)
1206 ("Not setting the epoch to %lu - testing only.\n"),
1208 else if (set_epoch_rtc(ctl
))
1210 ("Unable to set the epoch value in the kernel.\n"));
1213 # endif /* __alpha__ */
1214 #endif /* __linux__ */
1216 static void out_version(void)
1218 printf(UTIL_LINUX_VERSION
);
1222 * usage - Output (error and) usage information
1224 * This function is called both directly from main to show usage information
1225 * and as fatal function from shhopt if some argument is not understood. In
1226 * case of normal usage info FMT should be NULL. In that case the info is
1227 * printed to stdout. If FMT is given usage will act like fprintf( stderr,
1228 * fmt, ... ), show a usage information and terminate the program
1231 static void usage(const struct hwclock_control
*ctl
, const char *fmt
, ...)
1236 usageto
= fmt
? stderr
: stdout
;
1238 fputs(USAGE_HEADER
, usageto
);
1239 fputs(_(" hwclock [function] [option...]\n"), usageto
);
1241 fputs(USAGE_SEPARATOR
, usageto
);
1242 fputs(_("Query or set the hardware clock.\n"), usageto
);
1244 fputs(_("\nFunctions:\n"), usageto
);
1245 fputs(_(" -h, --help show this help text and exit\n"
1246 " -r, --show read hardware clock and print result\n"
1247 " --get read hardware clock and print drift corrected result\n"
1248 " --set set the RTC to the time given with --date\n"), usageto
);
1249 fputs(_(" -s, --hctosys set the system time from the hardware clock\n"
1250 " -w, --systohc set the hardware clock from the current system time\n"
1251 " --systz set the system time based on the current timezone\n"
1252 " --adjust adjust the RTC to account for systematic drift since\n"
1253 " the clock was last set or adjusted\n"), usageto
);
1255 fputs(_(" --getepoch print out the kernel's hardware clock epoch value\n"
1256 " --setepoch set the kernel's hardware clock epoch value to the \n"
1257 " value given with --epoch\n"), usageto
);
1259 fputs(_(" --predict predict RTC reading at time given with --date\n"
1260 " -V, --version display version information and exit\n"), usageto
);
1262 fputs(USAGE_OPTIONS
, usageto
);
1263 fputs(_(" -u, --utc the hardware clock is kept in UTC\n"
1264 " --localtime the hardware clock is kept in local time\n"), usageto
);
1266 fputs(_(" -f, --rtc <file> special /dev/... file to use instead of default\n"), usageto
);
1269 " --directisa access the ISA bus directly instead of %s\n"
1270 " --date <time> specifies the time to which to set the hardware clock\n"
1271 " --epoch <year> specifies the year which is the beginning of the\n"
1272 " hardware clock's epoch value\n"), _PATH_RTC_DEV
);
1274 " --update-drift update drift factor in %1$s (requires\n"
1275 " --set or --systohc)\n"
1276 " --noadjfile do not access %1$s; this requires the use of\n"
1277 " either --utc or --localtime\n"
1278 " --adjfile <file> specifies the path to the adjust file;\n"
1279 " the default is %1$s\n"), _PATH_ADJTIME
);
1280 fputs(_(" --test do not update anything, just show what would happen\n"
1281 " -D, --debug debugging mode\n" "\n"), usageto
);
1285 vfprintf(usageto
, fmt
, ap
);
1290 hwclock_exit(ctl
, fmt
? EX_USAGE
: EX_OK
);
1295 * EX_USAGE: bad invocation
1296 * EX_NOPERM: no permission
1297 * EX_OSFILE: cannot open /dev/rtc or /etc/adjtime
1298 * EX_IOERR: ioctl error getting or setting the time
1302 int main(int argc
, char **argv
)
1304 struct hwclock_control ctl
= { NULL
};
1305 struct timeval startup_time
;
1306 struct adjtime adjtime
= { 0 };
1307 struct timespec when
= { 0 };
1309 * The time we started up, in seconds into the epoch, including
1312 time_t set_time
= 0; /* Time to which user said to set Hardware Clock */
1315 /* Long only options. */
1317 OPT_ADJFILE
= CHAR_MAX
+ 1,
1333 static const struct option longopts
[] = {
1334 { "adjust", no_argument
, NULL
, 'a' },
1335 { "help", no_argument
, NULL
, 'h' },
1336 { "show", no_argument
, NULL
, 'r' },
1337 { "hctosys", no_argument
, NULL
, 's' },
1338 { "utc", no_argument
, NULL
, 'u' },
1339 { "version", no_argument
, NULL
, 'v' },
1340 { "systohc", no_argument
, NULL
, 'w' },
1341 { "debug", no_argument
, NULL
, 'D' },
1342 { "set", no_argument
, NULL
, OPT_SET
},
1344 { "getepoch", no_argument
, NULL
, OPT_GETEPOCH
},
1345 { "setepoch", no_argument
, NULL
, OPT_SETEPOCH
},
1347 { "noadjfile", no_argument
, NULL
, OPT_NOADJFILE
},
1348 { "localtime", no_argument
, NULL
, OPT_LOCALTIME
},
1349 { "directisa", no_argument
, NULL
, OPT_DIRECTISA
},
1350 { "test", no_argument
, NULL
, OPT_TEST
},
1351 { "date", required_argument
, NULL
, OPT_DATE
},
1352 { "epoch", required_argument
, NULL
, OPT_EPOCH
},
1354 { "rtc", required_argument
, NULL
, 'f' },
1356 { "adjfile", required_argument
, NULL
, OPT_ADJFILE
},
1357 { "systz", no_argument
, NULL
, OPT_SYSTZ
},
1358 { "predict-hc", no_argument
, NULL
, OPT_PREDICT_HC
},
1359 { "get", no_argument
, NULL
, OPT_GET
},
1360 { "update-drift", no_argument
, NULL
, OPT_UPDATE
},
1361 { NULL
, 0, NULL
, 0 }
1364 static const ul_excl_t excl
[] = { /* rows and cols in ASCII order */
1366 OPT_GET
, OPT_GETEPOCH
, OPT_PREDICT_HC
,
1367 OPT_SET
, OPT_SETEPOCH
, OPT_SYSTZ
},
1368 { 'u', OPT_LOCALTIME
},
1369 { OPT_ADJFILE
, OPT_NOADJFILE
},
1370 { OPT_NOADJFILE
, OPT_UPDATE
},
1373 int excl_st
[ARRAY_SIZE(excl
)] = UL_EXCL_STATUS_INIT
;
1375 /* Remember what time we were invoked */
1376 gettimeofday(&startup_time
, NULL
);
1378 #ifdef HAVE_LIBAUDIT
1379 hwaudit_fd
= audit_open();
1380 if (hwaudit_fd
< 0 && !(errno
== EINVAL
|| errno
== EPROTONOSUPPORT
||
1381 errno
== EAFNOSUPPORT
)) {
1383 * You get these error codes only when the kernel doesn't
1384 * have audit compiled in.
1386 warnx(_("Unable to connect to audit system"));
1390 setlocale(LC_ALL
, "");
1393 * We need LC_CTYPE and LC_TIME and LC_MESSAGES, but must avoid
1394 * LC_NUMERIC since it gives problems when we write to /etc/adjtime.
1395 * - gqueri@mail.dotcom.fr
1397 setlocale(LC_NUMERIC
, "C");
1399 bindtextdomain(PACKAGE
, LOCALEDIR
);
1400 textdomain(PACKAGE
);
1401 atexit(close_stdout
);
1403 while ((c
= getopt_long(argc
, argv
,
1404 "?hvVDarsuwAJSFf:", longopts
, NULL
)) != -1) {
1406 err_exclusive_options(c
, longopts
, excl
, excl_st
);
1442 ctl
.local_opt
= 1; /* --localtime */
1448 ctl
.testing
= 1; /* --test */
1451 ctl
.date_opt
= optarg
; /* --date */
1454 ctl
.epoch_option
= /* --epoch */
1455 strtoul_or_err(optarg
, _("invalid epoch argument"));
1458 ctl
.adj_file_name
= optarg
; /* --adjfile */
1461 ctl
.systz
= 1; /* --systz */
1463 case OPT_PREDICT_HC
:
1464 ctl
.predict
= 1; /* --predict-hc */
1467 ctl
.get
= 1; /* --get */
1470 ctl
.update
= 1; /* --update-drift */
1474 ctl
.rtc_dev_name
= optarg
; /* --rtc */
1477 case 'v': /* --version */
1481 case 'h': /* --help */
1491 #ifdef HAVE_LIBAUDIT
1493 if (ctl
.adjust
|| ctl
.hctosys
|| ctl
.systohc
||
1494 ctl
.set
|| ctl
.setepoch
) {
1500 usage(&ctl
, _("%s takes no non-option arguments. "
1501 "You supplied %d.\n"), program_invocation_short_name
,
1505 if (!ctl
.adj_file_name
)
1506 ctl
.adj_file_name
= _PATH_ADJTIME
;
1508 if (ctl
.noadjfile
&& !ctl
.utc
&& !ctl
.local_opt
) {
1509 warnx(_("With --noadjfile, you must specify "
1510 "either --utc or --localtime"));
1511 hwclock_exit(&ctl
, EX_USAGE
);
1514 if (ctl
.set
|| ctl
.predict
) {
1515 if (parse_date(&when
, ctl
.date_opt
, NULL
))
1516 set_time
= when
.tv_sec
;
1518 warnx(_("invalid date '%s'"), ctl
.date_opt
);
1519 hwclock_exit(&ctl
, EX_USAGE
);
1523 if (!(ctl
.show
| ctl
.set
| ctl
.systohc
| ctl
.hctosys
|
1524 ctl
.systz
| ctl
.adjust
| ctl
.getepoch
| ctl
.setepoch
|
1525 ctl
.predict
| ctl
.get
))
1526 ctl
.show
= 1; /* default to show */
1529 if (ctl
.getepoch
|| ctl
.setepoch
) {
1530 manipulate_epoch(&ctl
);
1531 hwclock_exit(&ctl
, EX_OK
);
1538 if (!ctl
.systz
&& !ctl
.predict
)
1539 determine_clock_access_method(&ctl
);
1541 if (!ctl
.noadjfile
&& !(ctl
.systz
&& (ctl
.utc
|| ctl
.local_opt
))) {
1542 if ((rc
= read_adjtime(&ctl
, &adjtime
)) != 0)
1543 hwclock_exit(&ctl
, rc
);
1545 /* Avoid writing adjtime file if we don't have to. */
1546 adjtime
.dirty
= FALSE
;
1547 ctl
.universal
= hw_clock_is_utc(&ctl
, adjtime
);
1548 rc
= manipulate_clock(&ctl
, set_time
, startup_time
, &adjtime
);
1549 hwclock_exit(&ctl
, rc
);
1550 return rc
; /* Not reached */
1553 void __attribute__((__noreturn__
))
1554 hwclock_exit(const struct hwclock_control
*ctl
1555 #ifndef HAVE_LIBAUDIT
1556 __attribute__((__unused__
))
1560 #ifdef HAVE_LIBAUDIT
1561 if (ctl
->hwaudit_on
) {
1562 audit_log_user_message(hwaudit_fd
, AUDIT_USYS_CONFIG
,
1563 "op=change-system-time", NULL
, NULL
, NULL
,
1572 * History of this program:
1574 * 98.08.12 BJH Version 2.4
1576 * Don't use century byte from Hardware Clock. Add comments telling why.
1578 * 98.06.20 BJH Version 2.3.
1580 * Make --hctosys set the kernel timezone from TZ environment variable
1581 * and/or /usr/lib/zoneinfo. From Klaus Ripke (klaus@ripke.com).
1583 * 98.03.05 BJH. Version 2.2.
1585 * Add --getepoch and --setepoch.
1587 * Fix some word length things so it works on Alpha.
1589 * Make it work when /dev/rtc doesn't have the interrupt functions. In this
1590 * case, busywait for the top of a second instead of blocking and waiting
1591 * for the update complete interrupt.
1593 * Fix a bunch of bugs too numerous to mention.
1595 * 97.06.01: BJH. Version 2.1. Read and write the century byte (Byte 50) of
1596 * the ISA Hardware Clock when using direct ISA I/O. Problem discovered by
1597 * job (jei@iclnl.icl.nl).
1599 * Use the rtc clock access method in preference to the KDGHWCLK method.
1600 * Problem discovered by Andreas Schwab <schwab@LS5.informatik.uni-dortmund.de>.
1602 * November 1996: Version 2.0.1. Modifications by Nicolai Langfeldt
1603 * (janl@math.uio.no) to make it compile on linux 1.2 machines as well as
1604 * more recent versions of the kernel. Introduced the NO_CLOCK access method
1605 * and wrote feature test code to detect absence of rtc headers.
1607 ***************************************************************************
1610 * To compile this, you must use GNU compiler optimization (-O option) in
1611 * order to make the "extern inline" functions from asm/io.h (inb(), etc.)
1612 * compile. If you don't optimize, which means the compiler will generate no
1613 * inline functions, the references to these functions in this program will
1614 * be compiled as external references. Since you probably won't be linking
1615 * with any functions by these names, you will have unresolved external
1616 * references when you link.
1618 * Here's some info on how we must deal with the time that elapses while
1619 * this program runs: There are two major delays as we run:
1621 * 1) Waiting up to 1 second for a transition of the Hardware Clock so
1622 * we are synchronized to the Hardware Clock.
1623 * 2) Running the "date" program to interpret the value of our --date
1626 * Reading the /etc/adjtime file is the next biggest source of delay and
1629 * The user wants to know what time it was at the moment he invoked us, not
1630 * some arbitrary time later. And in setting the clock, he is giving us the
1631 * time at the moment we are invoked, so if we set the clock some time
1632 * later, we have to add some time to that.
1634 * So we check the system time as soon as we start up, then run "date" and
1635 * do file I/O if necessary, then wait to synchronize with a Hardware Clock
1636 * edge, then check the system time again to see how much time we spent. We
1637 * immediately read the clock then and (if appropriate) report that time,
1638 * and additionally, the delay we measured.
1640 * If we're setting the clock to a time given by the user, we wait some more
1641 * so that the total delay is an integral number of seconds, then set the
1642 * Hardware Clock to the time the user requested plus that integral number
1643 * of seconds. N.B. The Hardware Clock can only be set in integral seconds.
1645 * If we're setting the clock to the system clock value, we wait for the
1646 * system clock to reach the top of a second, and then set the Hardware
1647 * Clock to the system clock's value.
1649 * Here's an interesting point about setting the Hardware Clock: On my
1650 * machine, when you set it, it sets to that precise time. But one can
1651 * imagine another clock whose update oscillator marches on a steady one
1652 * second period, so updating the clock between any two oscillator ticks is
1653 * the same as updating it right at the earlier tick. To avoid any
1654 * complications that might cause, we set the clock as soon as possible
1655 * after an oscillator tick.
1657 * About synchronizing to the Hardware Clock when reading the time: The
1658 * precision of the Hardware Clock counters themselves is one second. You
1659 * can't read the counters and find out that is 12:01:02.5. But if you
1660 * consider the location in time of the counter's ticks as part of its
1661 * value, then its precision is as infinite as time is continuous! What I'm
1662 * saying is this: To find out the _exact_ time in the hardware clock, we
1663 * wait until the next clock tick (the next time the second counter changes)
1664 * and measure how long we had to wait. We then read the value of the clock
1665 * counters and subtract the wait time and we know precisely what time it
1666 * was when we set out to query the time.
1668 * hwclock uses this method, and considers the Hardware Clock to have
1669 * infinite precision.