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