src/basic/clock-util.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010-2012 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24 #include <limits.h>
  25 #include <stdbool.h>
  26 #include <time.h>
  27 #include <linux/rtc.h>
  28 #include <stdio.h>
  29 #include <sys/ioctl.h>
  30 #include <sys/time.h>
  31
  32 #include "clock-util.h"
  33 #include "fd-util.h"
  34 #include "macro.h"
  35 #include "string-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(void) {
  74         _cleanup_fclose_ FILE *f;
  75
  76         /*
  77          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  78          *   # /etc/adjtime
  79          *   0.0 0 0
  80          *   0
  81          *   UTC
  82          */
  83         f = fopen("/etc/adjtime", "re");
  84         if (f) {
  85                 char line[LINE_MAX];
  86                 bool b;
  87
  88                 b = fgets(line, sizeof(line), f) &&
  89                         fgets(line, sizeof(line), f) &&
  90                         fgets(line, sizeof(line), f);
  91                 if (!b)
  92                         return -EIO;
  93
  94                 truncate_nl(line);
  95                 return streq(line, "LOCAL");
  96
  97         } else if (errno != ENOENT)
  98                 return -errno;
  99
 100         return 0;
 101 }
 102
 103 int clock_set_timezone(int *min) {
 104         const struct timeval *tv_null = NULL;
 105         struct timespec ts;
 106         struct tm *tm;
 107         int minutesdelta;
 108         struct timezone tz;
 109
 110         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 111         assert_se(tm = localtime(&ts.tv_sec));
 112         minutesdelta = tm->tm_gmtoff / 60;
 113
 114         tz.tz_minuteswest = -minutesdelta;
 115         tz.tz_dsttime = 0; /* DST_NONE */
 116
 117         /*
 118          * If the RTC does not run in UTC but in local time, the very first
 119          * call to settimeofday() will set the kernel's timezone and will warp the
 120          * system clock, so that it runs in UTC instead of the local time we
 121          * have read from the RTC.
 122          */
 123         if (settimeofday(tv_null, &tz) < 0)
 124                 return -errno;
 125         if (min)
 126                 *min = minutesdelta;
 127         return 0;
 128 }
 129
 130 int clock_reset_timewarp(void) {
 131         const struct timeval *tv_null = NULL;
 132         struct timezone tz;
 133
 134         tz.tz_minuteswest = 0;
 135         tz.tz_dsttime = 0; /* DST_NONE */
 136
 137         /*
 138          * The very first call to settimeofday() does time warp magic. Do a
 139          * dummy call here, so the time warping is sealed and all later calls
 140          * behave as expected.
 141          */
 142         if (settimeofday(tv_null, &tz) < 0)
 143                 return -errno;
 144
 145         return 0;
 146 }