libbb/rtc.c

   1 /*
   2  * Common RTC functions
   3  *
   4  * Licensed under GPLv2, see file LICENSE in this source tree.
   5  */
   6
   7 #include "libbb.h"
   8 #include "rtc_.h"
   9
  10 #if ENABLE_FEATURE_HWCLOCK_ADJTIME_FHS
  11 # define ADJTIME_PATH "/var/lib/hwclock/adjtime"
  12 #else
  13 # define ADJTIME_PATH "/etc/adjtime"
  14 #endif
  15
  16 int FAST_FUNC rtc_adjtime_is_utc(void)
  17 {
  18         int utc = 0;
  19         FILE *f = fopen_for_read(ADJTIME_PATH);
  20
  21         if (f) {
  22                 char buffer[128];
  23
  24                 while (fgets(buffer, sizeof(buffer), f)) {
  25                         if (is_prefixed_with(buffer, "UTC")) {
  26                                 utc = 1;
  27                                 break;
  28                         }
  29                 }
  30                 fclose(f);
  31         }
  32
  33         return utc;
  34 }
  35
  36 /* rtc opens are exclusive.
  37  * Try to run two "hwclock -w" at the same time to see it.
  38  * Users wouldn't expect that to fail merely because /dev/rtc
  39  * was momentarily busy, let's try a bit harder on errno == EBUSY.
  40  */
  41 static int open_loop_on_busy(const char *name, int flags)
  42 {
  43         int rtc;
  44         /*
  45          * Tested with two parallel "hwclock -w" loops.
  46          * With try = 10, no failures with 2x1000000 loop iterations.
  47          */
  48         int try = 1000 / 20;
  49  again:
  50         errno = 0;
  51         rtc = open(name, flags);
  52         if (errno == EBUSY) {
  53                 usleep(20 * 1000);
  54                 if (--try != 0)
  55                         goto again;
  56                 /* EBUSY. Last try, exit on error instead of returning -1 */
  57                 return xopen(name, flags);
  58         }
  59         return rtc;
  60 }
  61
  62 /* Never fails */
  63 int FAST_FUNC rtc_xopen(const char **default_rtc, int flags)
  64 {
  65         int rtc;
  66         const char *name =
  67                 "/dev/rtc""\0"
  68                 "/dev/rtc0""\0"
  69                 "/dev/misc/rtc""\0";
  70
  71         if (!*default_rtc)
  72                 goto try_name;
  73         name = ""; /*else: we have rtc name, don't try other names */
  74
  75         for (;;) {
  76                 rtc = open_loop_on_busy(*default_rtc, flags);
  77                 if (rtc >= 0)
  78                         return rtc;
  79                 if (!name[0])
  80                         return xopen(*default_rtc, flags);
  81  try_name:
  82                 *default_rtc = name;
  83                 name += strlen(name) + 1;
  84         }
  85 }
  86
  87 void FAST_FUNC rtc_read_tm(struct tm *ptm, int fd)
  88 {
  89         memset(ptm, 0, sizeof(*ptm));
  90         xioctl(fd, RTC_RD_TIME, ptm);
  91         ptm->tm_isdst = -1; /* "not known" */
  92 }
  93
  94 time_t FAST_FUNC rtc_tm2time(struct tm *ptm, int utc)
  95 {
  96         char *oldtz = oldtz; /* for compiler */
  97         time_t t;
  98
  99         if (utc) {
 100                 oldtz = getenv("TZ");
 101                 putenv((char*)"TZ=UTC0");
 102                 tzset();
 103         }
 104
 105         t = mktime(ptm);
 106
 107         if (utc) {
 108                 unsetenv("TZ");
 109                 if (oldtz)
 110                         putenv(oldtz - 3);
 111                 tzset();
 112         }
 113
 114         return t;
 115 }