src/basic/clock-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2010-2012 Lennart Poettering
   6 ***/
   7
   8 #include <errno.h>
   9 #include <fcntl.h>
  10 #include <limits.h>
  11 #include <stdbool.h>
  12 #include <time.h>
  13 #include <linux/rtc.h>
  14 #include <stdio.h>
  15 #include <sys/ioctl.h>
  16 #include <sys/time.h>
  17
  18 #include "clock-util.h"
  19 #include "fd-util.h"
  20 #include "macro.h"
  21 #include "string-util.h"
  22 #include "util.h"
  23
  24 int clock_get_hwclock(struct tm *tm) {
  25         _cleanup_close_ int fd = -1;
  26
  27         assert(tm);
  28
  29         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  30         if (fd < 0)
  31                 return -errno;
  32
  33         /* This leaves the timezone fields of struct tm
  34          * uninitialized! */
  35         if (ioctl(fd, RTC_RD_TIME, tm) < 0)
  36                 return -errno;
  37
  38         /* We don't know daylight saving, so we reset this in order not
  39          * to confuse mktime(). */
  40         tm->tm_isdst = -1;
  41
  42         return 0;
  43 }
  44
  45 int clock_set_hwclock(const struct tm *tm) {
  46         _cleanup_close_ int fd = -1;
  47
  48         assert(tm);
  49
  50         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  51         if (fd < 0)
  52                 return -errno;
  53
  54         if (ioctl(fd, RTC_SET_TIME, tm) < 0)
  55                 return -errno;
  56
  57         return 0;
  58 }
  59
  60 int clock_is_localtime(const char* adjtime_path) {
  61         _cleanup_fclose_ FILE *f;
  62
  63         if (!adjtime_path)
  64                 adjtime_path = "/etc/adjtime";
  65
  66         /*
  67          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  68          *   # /etc/adjtime
  69          *   0.0 0 0
  70          *   0
  71          *   UTC
  72          */
  73         f = fopen(adjtime_path, "re");
  74         if (f) {
  75                 char line[LINE_MAX];
  76                 bool b;
  77
  78                 b = fgets(line, sizeof(line), f) &&
  79                         fgets(line, sizeof(line), f) &&
  80                         fgets(line, sizeof(line), f);
  81                 if (!b)
  82                         /* less than three lines -> default to UTC */
  83                         return 0;
  84
  85                 truncate_nl(line);
  86                 return streq(line, "LOCAL");
  87
  88         } else if (errno != ENOENT)
  89                 return -errno;
  90
  91         /* adjtime not present -> default to UTC */
  92         return 0;
  93 }
  94
  95 int clock_set_timezone(int *min) {
  96         const struct timeval *tv_null = NULL;
  97         struct timespec ts;
  98         struct tm *tm;
  99         int minutesdelta;
 100         struct timezone tz;
 101
 102         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 103         assert_se(tm = localtime(&ts.tv_sec));
 104         minutesdelta = tm->tm_gmtoff / 60;
 105
 106         tz.tz_minuteswest = -minutesdelta;
 107         tz.tz_dsttime = 0; /* DST_NONE */
 108
 109         /*
 110          * If the RTC does not run in UTC but in local time, the very first
 111          * call to settimeofday() will set the kernel's timezone and will warp the
 112          * system clock, so that it runs in UTC instead of the local time we
 113          * have read from the RTC.
 114          */
 115         if (settimeofday(tv_null, &tz) < 0)
 116                 return negative_errno();
 117
 118         if (min)
 119                 *min = minutesdelta;
 120         return 0;
 121 }
 122
 123 int clock_reset_timewarp(void) {
 124         const struct timeval *tv_null = NULL;
 125         struct timezone tz;
 126
 127         tz.tz_minuteswest = 0;
 128         tz.tz_dsttime = 0; /* DST_NONE */
 129
 130         /*
 131          * The very first call to settimeofday() does time warp magic. Do a
 132          * dummy call here, so the time warping is sealed and all later calls
 133          * behave as expected.
 134          */
 135         if (settimeofday(tv_null, &tz) < 0)
 136                 return -errno;
 137
 138         return 0;
 139 }
 140
 141 #define TIME_EPOCH_USEC ((usec_t) TIME_EPOCH * USEC_PER_SEC)
 142
 143 int clock_apply_epoch(void) {
 144         struct timespec ts;
 145
 146         if (now(CLOCK_REALTIME) >= TIME_EPOCH_USEC)
 147                 return 0;
 148
 149         if (clock_settime(CLOCK_REALTIME, timespec_store(&ts, TIME_EPOCH_USEC)) < 0)
 150                 return -errno;
 151
 152         return 1;
 153 }