main: add option to print configuration

Add -p option to chronyd to print lines from the configuration as they
are parsed and exit. It can be used to verify the syntax and get the
whole configuration when it is split into multiple files.

conf.c

@@ -85,6 +85,7 @@ static void parse_tempcomp(char *);
 /* ================================================== */
 /* Configuration variables */
 
+static int print_config = 0;
 static int restarted = 0;
 static char *rtc_device;
 static int acquisition_port = -1;
@@ -439,6 +440,14 @@ CNF_Finalise(void)
 
 /* ================================================== */
 
+void
+CNF_EnablePrint(void)
+{
+  print_config = 1;
+}
+
+/* ================================================== */
+
 /* Read the configuration file */
 void
 CNF_ReadFile(const char *filename)
@@ -489,6 +498,9 @@ CNF_ParseLine(const char *filename, int number, char *line)
   processed_command = command = line;
   p = CPS_SplitWord(line);
 
+  if (print_config && strcasecmp(command, "include") && strcasecmp(command, "confdirs"))
+    printf("%s%s%s\n", command, p[0] != '\0' ? " " : "", p);
+
   if (!strcasecmp(command, "acquisitionport")) {
     parse_int(p, &acquisition_port);
   } else if (!strcasecmp(command, "allow")) {

conf.h

@@ -35,6 +35,8 @@
 extern void CNF_Initialise(int restarted, int client_only);
 extern void CNF_Finalise(void);
 
+extern void CNF_EnablePrint(void);
+
 extern char *CNF_GetRtcDevice(void);
 
 extern void CNF_ReadFile(const char *filename);

doc/chronyd.adoc

@@ -76,6 +76,12 @@ the log file, syslog, or terminal. The following levels can be specified:
 0 (informational), 1 (warning), 2 (non-fatal error), and 3 (fatal error). The
 default value is 0.
 
+*-p*::
+When run in this mode, *chronyd* will print the configuration and exit. It will
+not detach from the terminal. This option can be used to verify the syntax of
+the configuration and get the whole configuration, even if it is split into
+multiple files and read by the *include* or *confdirs* directive.
+
 *-q*::
 When run in this mode, *chronyd* will set the system clock once and exit. It
 will not detach from the terminal.

main.c

@@ -373,7 +373,7 @@ go_daemon(void)
 static void
 print_help(const char *progname)
 {
-      printf("Usage: %s [-4|-6] [-n|-d] [-q|-Q] [-r] [-R] [-s] [-t TIMEOUT] [-f FILE|COMMAND...]\n",
+      printf("Usage: %s [-4|-6] [-n|-d] [-p|-q|-Q] [-r] [-R] [-s] [-t TIMEOUT] [-f FILE|COMMAND...]\n",
              progname);
 }
 
@@ -410,7 +410,7 @@ int main
   int do_init_rtc = 0, restarted = 0, client_only = 0, timeout = -1;
   int scfilter_level = 0, lock_memory = 0, sched_priority = 0;
   int clock_control = 1, system_log = 1, log_severity = LOGS_INFO;
-  int config_args = 0;
+  int config_args = 0, print_config = 0;
 
   do_platform_checks();
 
@@ -430,7 +430,7 @@ int main
   optind = 1;
 
   /* Parse short command-line options */
-  while ((opt = getopt(argc, argv, "46df:F:hl:L:mnP:qQrRst:u:vx")) != -1) {
+  while ((opt = getopt(argc, argv, "46df:F:hl:L:mnpP:qQrRst:u:vx")) != -1) {
     switch (opt) {
       case '4':
       case '6':
@@ -459,6 +459,12 @@ int main
       case 'n':
         nofork = 1;
         break;
+      case 'p':
+        print_config = 1;
+        client_only = 1;
+        nofork = 1;
+        system_log = 0;
+        break;
       case 'P':
         sched_priority = parse_int_arg(optarg);
         break;
@@ -523,6 +529,8 @@ int main
   DNS_SetAddressFamily(address_family);
 
   CNF_Initialise(restarted, client_only);
+  if (print_config)
+    CNF_EnablePrint();
 
   /* Parse the config file or the remaining command line arguments */
   config_args = argc - optind;
@@ -533,6 +541,9 @@ int main
       CNF_ParseLine(NULL, config_args + optind - argc + 1, argv[optind]);
   }
 
+  if (print_config)
+    return 0;
+
   /* Check whether another chronyd may already be running */
   check_pidfile();