src/basic/clock-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   Copyright 2010-2012 Lennart Poettering
   4 ***/
   5
   6 #include <errno.h>
   7 #include <fcntl.h>
   8 #include <limits.h>
   9 #include <stdbool.h>
  10 #include <time.h>
  11 #include <linux/rtc.h>
  12 #include <stdio.h>
  13 #include <sys/ioctl.h>
  14 #include <sys/time.h>
  15
  16 #include "clock-util.h"
  17 #include "fd-util.h"
  18 #include "macro.h"
  19 #include "string-util.h"
  20 #include "util.h"
  21
  22 int clock_get_hwclock(struct tm *tm) {
  23         _cleanup_close_ int fd = -1;
  24
  25         assert(tm);
  26
  27         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  28         if (fd < 0)
  29                 return -errno;
  30
  31         /* This leaves the timezone fields of struct tm
  32          * uninitialized! */
  33         if (ioctl(fd, RTC_RD_TIME, tm) < 0)
  34                 return -errno;
  35
  36         /* We don't know daylight saving, so we reset this in order not
  37          * to confuse mktime(). */
  38         tm->tm_isdst = -1;
  39
  40         return 0;
  41 }
  42
  43 int clock_set_hwclock(const struct tm *tm) {
  44         _cleanup_close_ int fd = -1;
  45
  46         assert(tm);
  47
  48         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  49         if (fd < 0)
  50                 return -errno;
  51
  52         if (ioctl(fd, RTC_SET_TIME, tm) < 0)
  53                 return -errno;
  54
  55         return 0;
  56 }
  57
  58 int clock_is_localtime(const char* adjtime_path) {
  59         _cleanup_fclose_ FILE *f;
  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                 char line[LINE_MAX];
  74                 bool b;
  75
  76                 b = fgets(line, sizeof(line), f) &&
  77                         fgets(line, sizeof(line), f) &&
  78                         fgets(line, sizeof(line), f);
  79                 if (!b)
  80                         /* less than three lines -> default to UTC */
  81                         return 0;
  82
  83                 truncate_nl(line);
  84                 return streq(line, "LOCAL");
  85
  86         } else if (errno != ENOENT)
  87                 return -errno;
  88
  89         /* adjtime not present -> default to UTC */
  90         return 0;
  91 }
  92
  93 int clock_set_timezone(int *min) {
  94         const struct timeval *tv_null = NULL;
  95         struct timespec ts;
  96         struct tm *tm;
  97         int minutesdelta;
  98         struct timezone tz;
  99
 100         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 101         assert_se(tm = localtime(&ts.tv_sec));
 102         minutesdelta = tm->tm_gmtoff / 60;
 103
 104         tz.tz_minuteswest = -minutesdelta;
 105         tz.tz_dsttime = 0; /* DST_NONE */
 106
 107         /*
 108          * If the RTC does not run in UTC but in local time, the very first
 109          * call to settimeofday() will set the kernel's timezone and will warp the
 110          * system clock, so that it runs in UTC instead of the local time we
 111          * have read from the RTC.
 112          */
 113         if (settimeofday(tv_null, &tz) < 0)
 114                 return negative_errno();
 115
 116         if (min)
 117                 *min = minutesdelta;
 118         return 0;
 119 }
 120
 121 int clock_reset_timewarp(void) {
 122         const struct timeval *tv_null = NULL;
 123         struct timezone tz;
 124
 125         tz.tz_minuteswest = 0;
 126         tz.tz_dsttime = 0; /* DST_NONE */
 127
 128         /*
 129          * The very first call to settimeofday() does time warp magic. Do a
 130          * dummy call here, so the time warping is sealed and all later calls
 131          * behave as expected.
 132          */
 133         if (settimeofday(tv_null, &tz) < 0)
 134                 return -errno;
 135
 136         return 0;
 137 }
 138
 139 #define TIME_EPOCH_USEC ((usec_t) TIME_EPOCH * USEC_PER_SEC)
 140
 141 int clock_apply_epoch(void) {
 142         struct timespec ts;
 143
 144         if (now(CLOCK_REALTIME) >= TIME_EPOCH_USEC)
 145                 return 0;
 146
 147         if (clock_settime(CLOCK_REALTIME, timespec_store(&ts, TIME_EPOCH_USEC)) < 0)
 148                 return -errno;
 149
 150         return 1;
 151 }