src/shared/clock-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <stdio.h>
   4 #include <sys/time.h>
   5
   6 #include "alloc-util.h"
   7 #include "clock-util.h"
   8 #include "fd-util.h"
   9 #include "fileio.h"
  10 #include "string-util.h"
  11 #include "time-util.h"
  12
  13 int clock_is_localtime(const char *adjtime_path) {
  14         int r;
  15
  16         if (!adjtime_path)
  17                 adjtime_path = "/etc/adjtime";
  18
  19         /*
  20          * The third line of adjtime is "UTC" or "LOCAL" or nothing.
  21          *   # /etc/adjtime
  22          *   0.0 0 0
  23          *   0
  24          *   UTC
  25          */
  26         _cleanup_fclose_ FILE *f = fopen(adjtime_path, "re");
  27         if (!f) {
  28                 if (errno != ENOENT)
  29                         return -errno;
  30
  31                 /* adjtime_path not present → default to UTC */
  32                 return false;
  33         }
  34
  35         _cleanup_free_ char *line = NULL;
  36         for (unsigned i = 0; i < 2; i++) { /* skip the first two lines */
  37                 r = read_line(f, LONG_LINE_MAX, NULL);
  38                 if (r < 0)
  39                         return r;
  40                 if (r == 0)
  41                         return false; /* less than three lines → default to UTC */
  42         }
  43
  44         r = read_line(f, LONG_LINE_MAX, &line);
  45         if (r < 0)
  46                 return r;
  47         if (r == 0)
  48                 return false; /* less than three lines → default to UTC */
  49
  50         return streq(line, "LOCAL");
  51 }
  52
  53 int clock_set_timezone(int *ret_minutesdelta) {
  54         struct tm tm;
  55         int r;
  56
  57         r = localtime_or_gmtime_usec(now(CLOCK_REALTIME), /* utc= */ false, &tm);
  58         if (r < 0)
  59                 return r;
  60
  61         int minutesdelta = tm.tm_gmtoff / 60;
  62
  63         struct timezone tz = {
  64                 .tz_minuteswest = -minutesdelta,
  65                 .tz_dsttime = 0, /* DST_NONE */
  66         };
  67
  68         /* If the RTC does not run in UTC but in local time, the very first call to settimeofday() will set
  69          * the kernel's timezone and will warp the system clock, so that it runs in UTC instead of the local
  70          * time we have read from the RTC. */
  71         if (settimeofday(NULL, &tz) < 0)
  72                 return -errno;
  73
  74         if (ret_minutesdelta)
  75                 *ret_minutesdelta = minutesdelta;
  76
  77         return 0;
  78 }