src/basic/clock-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <limits.h>
   6 #include <stdbool.h>
   7 #include <time.h>
   8 #include <linux/rtc.h>
   9 #include <stdio.h>
  10 #include <sys/ioctl.h>
  11 #include <sys/time.h>
  12
  13 #include "alloc-util.h"
  14 #include "clock-util.h"
  15 #include "fd-util.h"
  16 #include "fileio.h"
  17 #include "macro.h"
  18 #include "string-util.h"
  19 #include "util.h"
  20
  21 int clock_get_hwclock(struct tm *tm) {
  22         _cleanup_close_ int fd = -1;
  23
  24         assert(tm);
  25
  26         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  27         if (fd < 0)
  28                 return -errno;
  29
  30         /* This leaves the timezone fields of struct tm
  31          * uninitialized! */
  32         if (ioctl(fd, RTC_RD_TIME, tm) < 0)
  33                 return -errno;
  34
  35         /* We don't know daylight saving, so we reset this in order not
  36          * to confuse mktime(). */
  37         tm->tm_isdst = -1;
  38
  39         return 0;
  40 }
  41
  42 int clock_set_hwclock(const struct tm *tm) {
  43         _cleanup_close_ int fd = -1;
  44
  45         assert(tm);
  46
  47         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  48         if (fd < 0)
  49                 return -errno;
  50
  51         if (ioctl(fd, RTC_SET_TIME, tm) < 0)
  52                 return -errno;
  53
  54         return 0;
  55 }
  56
  57 int clock_is_localtime(const char* adjtime_path) {
  58         _cleanup_fclose_ FILE *f;
  59         int r;
  60
  61         if (!adjtime_path)
  62                 adjtime_path = "/etc/adjtime";
  63
  64         /*
  65          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  66          *   # /etc/adjtime
  67          *   0.0 0 0
  68          *   0
  69          *   UTC
  70          */
  71         f = fopen(adjtime_path, "re");
  72         if (f) {
  73                 _cleanup_free_ char *line = NULL;
  74                 unsigned i;
  75
  76                 for (i = 0; i < 2; i++) { /* skip the first two lines */
  77                         r = read_line(f, LONG_LINE_MAX, NULL);
  78                         if (r < 0)
  79                                 return r;
  80                         if (r == 0)
  81                                 return false; /* less than three lines → default to UTC */
  82                 }
  83
  84                 r = read_line(f, LONG_LINE_MAX, &line);
  85                 if (r < 0)
  86                         return r;
  87                 if (r == 0)
  88                         return false; /* less than three lines → default to UTC */
  89
  90                 return streq(line, "LOCAL");
  91
  92         } else if (errno != ENOENT)
  93                 return -errno;
  94
  95         /* adjtime not present → default to UTC */
  96         return false;
  97 }
  98
  99 int clock_set_timezone(int *min) {
 100         const struct timeval *tv_null = NULL;
 101         struct timespec ts;
 102         struct tm tm;
 103         int minutesdelta;
 104         struct timezone tz;
 105
 106         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 107         assert_se(localtime_r(&ts.tv_sec, &tm));
 108         minutesdelta = tm.tm_gmtoff / 60;
 109
 110         tz.tz_minuteswest = -minutesdelta;
 111         tz.tz_dsttime = 0; /* DST_NONE */
 112
 113         /*
 114          * If the RTC does not run in UTC but in local time, the very first
 115          * call to settimeofday() will set the kernel's timezone and will warp the
 116          * system clock, so that it runs in UTC instead of the local time we
 117          * have read from the RTC.
 118          */
 119         if (settimeofday(tv_null, &tz) < 0)
 120                 return negative_errno();
 121
 122         if (min)
 123                 *min = minutesdelta;
 124         return 0;
 125 }
 126
 127 int clock_reset_timewarp(void) {
 128         const struct timeval *tv_null = NULL;
 129         struct timezone tz;
 130
 131         tz.tz_minuteswest = 0;
 132         tz.tz_dsttime = 0; /* DST_NONE */
 133
 134         /*
 135          * The very first call to settimeofday() does time warp magic. Do a
 136          * dummy call here, so the time warping is sealed and all later calls
 137          * behave as expected.
 138          */
 139         if (settimeofday(tv_null, &tz) < 0)
 140                 return -errno;
 141
 142         return 0;
 143 }
 144
 145 #define TIME_EPOCH_USEC ((usec_t) TIME_EPOCH * USEC_PER_SEC)
 146
 147 int clock_apply_epoch(void) {
 148         struct timespec ts;
 149
 150         if (now(CLOCK_REALTIME) >= TIME_EPOCH_USEC)
 151                 return 0;
 152
 153         if (clock_settime(CLOCK_REALTIME, timespec_store(&ts, TIME_EPOCH_USEC)) < 0)
 154                 return -errno;
 155
 156         return 1;
 157 }