weston: add wait-for-debugger option

When you need to start Weston via weston-launch, systemd unit, or any
other runner, it is annoying to try to get in with a debugger,
especially if the thing you are interested in happens at start-up. To
make it easy, a new option is introduced.

The new option, implemented both as a command line option and a
weston.ini option, raises SIGSTOP early in the start-up, before the
weston_compositor has been created. This allows one to attach a debugger
at a known point in execution, and resume execution with SIGCONT.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Ian Ray <ian.ray@ge.com>

compositor/main.c

@@ -557,6 +557,7 @@ usage(int error_code)
 		"  --log=FILE\t\tLog to the given file\n"
 		"  -c, --config=FILE\tConfig file to load, defaults to weston.ini\n"
 		"  --no-config\t\tDo not read weston.ini\n"
+		"  --wait-for-debugger\tRaise SIGSTOP on start-up\n"
 		"  -h, --help\t\tThis help message\n\n");
 
 #if defined(BUILD_DRM_COMPOSITOR)
@@ -1787,6 +1788,7 @@ int main(int argc, char *argv[])
 	struct weston_seat *seat;
 	struct wet_compositor user_data;
 	int require_input;
+	int32_t wait_for_debugger = 0;
 
 	const struct weston_option core_options[] = {
 		{ WESTON_OPTION_STRING, "backend", 'B', &backend },
@@ -1800,6 +1802,7 @@ int main(int argc, char *argv[])
 		{ WESTON_OPTION_BOOLEAN, "version", 0, &version },
 		{ WESTON_OPTION_BOOLEAN, "no-config", 0, &noconfig },
 		{ WESTON_OPTION_STRING, "config", 'c', &config_file },
+		{ WESTON_OPTION_BOOLEAN, "wait-for-debugger", 0, &wait_for_debugger },
 	};
 
 	if (os_fd_set_cloexec(fileno(stdin))) {
@@ -1863,6 +1866,16 @@ int main(int argc, char *argv[])
 
 	section = weston_config_get_section(config, "core", NULL, NULL);
 
+	if (!wait_for_debugger)
+		weston_config_section_get_bool(section, "wait-for-debugger",
+					       &wait_for_debugger, 0);
+	if (wait_for_debugger) {
+		weston_log("Weston PID is %ld - "
+			   "waiting for debugger, send SIGCONT to continue...\n",
+			   (long)getpid());
+		raise(SIGSTOP);
+	}
+
 	if (!backend) {
 		weston_config_section_get_string(section, "backend", &backend,
 						 NULL);