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