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   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <limits.h>
  24 #include <stdbool.h>
  25 #include <time.h>
  26 #include <linux/rtc.h>
  27 #include <stdio.h>
  28 #include <sys/ioctl.h>
  29 #include <sys/time.h>
  30
  31 #include "clock-util.h"
  32 #include "fd-util.h"
  33 #include "macro.h"
  34 #include "string-util.h"
  35 #include "util.h"
  36
  37 int clock_get_hwclock(struct tm *tm) {
  38         _cleanup_close_ int fd = -1;
  39
  40         assert(tm);
  41
  42         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  43         if (fd < 0)
  44                 return -errno;
  45
  46         /* This leaves the timezone fields of struct tm
  47          * uninitialized! */
  48         if (ioctl(fd, RTC_RD_TIME, tm) < 0)
  49                 return -errno;
  50
  51         /* We don't know daylight saving, so we reset this in order not
  52          * to confuse mktime(). */
  53         tm->tm_isdst = -1;
  54
  55         return 0;
  56 }
  57
  58 int clock_set_hwclock(const struct tm *tm) {
  59         _cleanup_close_ int fd = -1;
  60
  61         assert(tm);
  62
  63         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  64         if (fd < 0)
  65                 return -errno;
  66
  67         if (ioctl(fd, RTC_SET_TIME, tm) < 0)
  68                 return -errno;
  69
  70         return 0;
  71 }
  72
  73 int clock_is_localtime(const char* adjtime_path) {
  74         _cleanup_fclose_ FILE *f;
  75
  76         if (!adjtime_path)
  77                 adjtime_path = "/etc/adjtime";
  78
  79         /*
  80          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  81          *   # /etc/adjtime
  82          *   0.0 0 0
  83          *   0
  84          *   UTC
  85          */
  86         f = fopen(adjtime_path, "re");
  87         if (f) {
  88                 char line[LINE_MAX];
  89                 bool b;
  90
  91                 b = fgets(line, sizeof(line), f) &&
  92                         fgets(line, sizeof(line), f) &&
  93                         fgets(line, sizeof(line), f);
  94                 if (!b)
  95                         /* less than three lines -> default to UTC */
  96                         return 0;
  97
  98                 truncate_nl(line);
  99                 return streq(line, "LOCAL");
 100
 101         } else if (errno != ENOENT)
 102                 return -errno;
 103
 104         /* adjtime not present -> default to UTC */
 105         return 0;
 106 }
 107
 108 int clock_set_timezone(int *min) {
 109         const struct timeval *tv_null = NULL;
 110         struct timespec ts;
 111         struct tm *tm;
 112         int minutesdelta;
 113         struct timezone tz;
 114
 115         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 116         assert_se(tm = localtime(&ts.tv_sec));
 117         minutesdelta = tm->tm_gmtoff / 60;
 118
 119         tz.tz_minuteswest = -minutesdelta;
 120         tz.tz_dsttime = 0; /* DST_NONE */
 121
 122         /*
 123          * If the RTC does not run in UTC but in local time, the very first
 124          * call to settimeofday() will set the kernel's timezone and will warp the
 125          * system clock, so that it runs in UTC instead of the local time we
 126          * have read from the RTC.
 127          */
 128         if (settimeofday(tv_null, &tz) < 0)
 129                 return negative_errno();
 130
 131         if (min)
 132                 *min = minutesdelta;
 133         return 0;
 134 }
 135
 136 int clock_reset_timewarp(void) {
 137         const struct timeval *tv_null = NULL;
 138         struct timezone tz;
 139
 140         tz.tz_minuteswest = 0;
 141         tz.tz_dsttime = 0; /* DST_NONE */
 142
 143         /*
 144          * The very first call to settimeofday() does time warp magic. Do a
 145          * dummy call here, so the time warping is sealed and all later calls
 146          * behave as expected.
 147          */
 148         if (settimeofday(tv_null, &tz) < 0)
 149                 return -errno;
 150
 151         return 0;
 152 }
 153
 154 #define TIME_EPOCH_USEC ((usec_t) TIME_EPOCH * USEC_PER_SEC)
 155
 156 int clock_apply_epoch(void) {
 157         struct timespec ts;
 158
 159         if (now(CLOCK_REALTIME) >= TIME_EPOCH_USEC)
 160                 return 0;
 161
 162         if (clock_settime(CLOCK_REALTIME, timespec_store(&ts, TIME_EPOCH_USEC)) < 0)
 163                 return -errno;
 164
 165         return 1;
 166 }