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 "clock-util.h"
  30 #include "fd-util.h"
  31 #include "macro.h"
  32 #include "string-util.h"
  33 #include "util.h"
  34
  35 int clock_get_hwclock(struct tm *tm) {
  36         _cleanup_close_ int fd = -1;
  37
  38         assert(tm);
  39
  40         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  41         if (fd < 0)
  42                 return -errno;
  43
  44         /* This leaves the timezone fields of struct tm
  45          * uninitialized! */
  46         if (ioctl(fd, RTC_RD_TIME, tm) < 0)
  47                 return -errno;
  48
  49         /* We don't know daylight saving, so we reset this in order not
  50          * to confuse mktime(). */
  51         tm->tm_isdst = -1;
  52
  53         return 0;
  54 }
  55
  56 int clock_set_hwclock(const struct tm *tm) {
  57         _cleanup_close_ int fd = -1;
  58
  59         assert(tm);
  60
  61         fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
  62         if (fd < 0)
  63                 return -errno;
  64
  65         if (ioctl(fd, RTC_SET_TIME, tm) < 0)
  66                 return -errno;
  67
  68         return 0;
  69 }
  70
  71 int clock_is_localtime(void) {
  72         _cleanup_fclose_ FILE *f;
  73
  74         /*
  75          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  76          *   # /etc/adjtime
  77          *   0.0 0 0
  78          *   0
  79          *   UTC
  80          */
  81         f = fopen("/etc/adjtime", "re");
  82         if (f) {
  83                 char line[LINE_MAX];
  84                 bool b;
  85
  86                 b = fgets(line, sizeof(line), f) &&
  87                         fgets(line, sizeof(line), f) &&
  88                         fgets(line, sizeof(line), f);
  89                 if (!b)
  90                         return -EIO;
  91
  92                 truncate_nl(line);
  93                 return streq(line, "LOCAL");
  94
  95         } else if (errno != ENOENT)
  96                 return -errno;
  97
  98         return 0;
  99 }
 100
 101 int clock_set_timezone(int *min) {
 102         const struct timeval *tv_null = NULL;
 103         struct timespec ts;
 104         struct tm *tm;
 105         int minutesdelta;
 106         struct timezone tz;
 107
 108         assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
 109         assert_se(tm = localtime(&ts.tv_sec));
 110         minutesdelta = tm->tm_gmtoff / 60;
 111
 112         tz.tz_minuteswest = -minutesdelta;
 113         tz.tz_dsttime = 0; /* DST_NONE */
 114
 115         /*
 116          * If the RTC does not run in UTC but in local time, the very first
 117          * call to settimeofday() will set the kernel's timezone and will warp the
 118          * system clock, so that it runs in UTC instead of the local time we
 119          * have read from the RTC.
 120          */
 121         if (settimeofday(tv_null, &tz) < 0)
 122                 return -errno;
 123         if (min)
 124                 *min = minutesdelta;
 125         return 0;
 126 }
 127
 128 int clock_reset_timewarp(void) {
 129         const struct timeval *tv_null = NULL;
 130         struct timezone tz;
 131
 132         tz.tz_minuteswest = 0;
 133         tz.tz_dsttime = 0; /* DST_NONE */
 134
 135         /*
 136          * The very first call to settimeofday() does time warp magic. Do a
 137          * dummy call here, so the time warping is sealed and all later calls
 138          * behave as expected.
 139          */
 140         if (settimeofday(tv_null, &tz) < 0)
 141                 return -errno;
 142
 143         return 0;
 144 }