smartdns: add argument -R support auto restart smartdns for docker.

src/smartdns.c

@@ -47,6 +47,7 @@
 #include <sys/resource.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/wait.h>
 #include <syslog.h>
 #include <ucontext.h>
 
@@ -153,6 +154,7 @@ static void _help(void)
 		"  -f            run foreground.\n"
 		"  -c [conf]     config file.\n"
 		"  -p [pid]      pid file path, '-' means don't create pid file.\n"
+		"  -R            restart smartdns when crash.\n"
 		"  -S            ignore segment fault signal.\n"
 		"  -x            verbose screen.\n"
 		"  -v            display version.\n"
@@ -771,6 +773,56 @@ static void _smartdns_early_log(struct tlog_loginfo *loginfo, const char *format
 	syslog(sys_log_level, "%s", log_buf);
 }
 
+static int _smartdns_child_pid = 0;
+
+static void _smartdns_run_as_init_sig(int sig)
+{
+	if (_smartdns_child_pid > 0) {
+		kill(_smartdns_child_pid, SIGTERM);
+		waitpid(_smartdns_child_pid, NULL, 0);
+	}
+
+	_exit(0);
+}
+
+static int _smartdns_run_as_init(int restart_when_crash)
+{
+	pid_t pid;
+
+	if (restart_when_crash == 0) {
+		return 0;
+	}
+
+	pid = getpid();
+	setpgid(pid, pid);
+
+restart:
+	pid = fork();
+	if (pid < 0) {
+		fprintf(stderr, "fork failed, %s\n", strerror(errno));
+		return -1;
+	} else if (pid == 0) {
+		return 0;
+	}
+
+	_smartdns_child_pid = pid;
+
+	signal(SIGTERM, _smartdns_run_as_init_sig);
+
+	while (true) {
+		pid = waitpid(-1, NULL, 0);
+		if (pid == _smartdns_child_pid) {
+			goto restart;
+		}
+
+		if (pid < 0) {
+			sleep(1);
+		}
+	}
+
+	return -1;
+}
+
 #ifdef TEST
 
 static smartdns_post_func _smartdns_post = NULL;
@@ -815,6 +867,7 @@ int main(int argc, char *argv[])
 	char pid_file[MAX_LINE_LEN];
 	int is_pid_file_set = 0;
 	int signal_ignore = 0;
+	int restart_when_crash = getpid() == 1 ? 1 : 0;
 	sigset_t empty_sigblock;
 	struct stat sb;
 
@@ -834,7 +887,7 @@ int main(int argc, char *argv[])
 	sigprocmask(SIG_SETMASK, &empty_sigblock, NULL);
 	smartdns_close_allfds();
 
-	while ((opt = getopt_long(argc, argv, "fhc:p:SvxN:", long_options, NULL)) != -1) {
+	while ((opt = getopt_long(argc, argv, "fhc:p:SvxN:R", long_options, NULL)) != -1) {
 		switch (opt) {
 		case 'f':
 			is_run_as_daemon = 0;
@@ -850,6 +903,9 @@ int main(int argc, char *argv[])
 				is_pid_file_set = 1;
 			}
 			break;
+		case 'R':
+			restart_when_crash = 1;
+			break;
 		case 'S':
 			signal_ignore = 1;
 			break;
@@ -876,6 +932,10 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	if (_smartdns_run_as_init(restart_when_crash) != 0) {
+		return 1;
+	}
+
 	srand(time(NULL));
 
 	tlog_reg_early_printf_callback(_smartdns_early_log);