main: add -t option to chronyd

This option sets a timeout (in seconds) after which chronyd will exit.
If the clock is not synchronised, it will exit with a non-zero status.
This is useful with the -q or -Q option to shorten the maximum time
waiting for measurements, or with the -r option to limit the time when
chronyd is running, but still allow it to adjust the frequency of the
system clock.

doc/chronyd.adoc

@@ -110,6 +110,13 @@ time and the RTC time, the system time will be set to it to restore the time
 when *chronyd* was previously stopped. This is useful on computers that have no
 RTC or the RTC is broken (e.g. it has no battery).
 
+*-t* _timeout_::
+This option sets a timeout (in seconds) after which *chronyd* will exit. If the
+clock is not synchronised, it will exit with a non-zero status. This is useful
+with the *-q* or *-Q* option to shorten the maximum time waiting for
+measurements, or with the *-r* option to limit the time when *chronyd* is
+running, but still allow it to adjust the frequency of the system clock.
+
 *-u* _user_::
 This option sets the name of the system user to which *chronyd* will switch
 after start in order to drop root privileges. It overrides the

main.c

@@ -145,6 +145,16 @@ signal_cleanup(int x)
 
 /* ================================================== */
 
+static void
+quit_timeout(void *arg)
+{
+  /* Return with non-zero status if the clock is not synchronised */
+  exit_status = REF_GetOurStratum() >= NTP_MAX_STRATUM;
+  SCH_QuitProgram();
+}
+
+/* ================================================== */
+
 static void
 ntp_source_resolving_end(void)
 {
@@ -362,7 +372,7 @@ int main
   char *user = NULL;
   struct passwd *pw;
   int debug = 0, nofork = 0, address_family = IPADDR_UNSPEC;
-  int do_init_rtc = 0, restarted = 0;
+  int do_init_rtc = 0, restarted = 0, timeout = 0;
   int other_pid;
   int scfilter_level = 0, lock_memory = 0, sched_priority = 0;
   int system_log = 1;
@@ -420,6 +430,10 @@ int main
       ref_mode = REF_ModePrintOnce;
       nofork = 1;
       system_log = 0;
+    } else if (!strcmp("-t", *argv)) {
+      ++argv, --argc;
+      if (argc == 0 || sscanf(*argv, "%d", &timeout) != 1 || timeout <= 0)
+        LOG_FATAL(LOGF_Main, "Bad timeout");
     } else if (!strcmp("-4", *argv)) {
       address_family = IPADDR_INET4;
     } else if (!strcmp("-6", *argv)) {
@@ -549,6 +563,9 @@ int main
   REF_SetModeEndHandler(reference_mode_end);
   REF_SetMode(ref_mode);
 
+  if (timeout)
+    SCH_AddTimeoutByDelay(timeout, quit_timeout, NULL);
+
   if (do_init_rtc) {
     RTC_TimeInit(post_init_rtc_hook, NULL);
   } else {