Add -S|--session <command> option

...to start <command> on startup and to terminate the compositor when
<command> exits.

This is useful for session management as it allows the session client (for
example `lxqt-session`) to terminate labwc - be exiting itself.

Under X, xinit starts the server and keeps it alive for as long as
lxqt-session runs. Thus either the session client starts the Window
Manager, or the Window Manager can be launched independently first.  On
Wayland, the Compositor is both Display Server and Window Manager, so the
described session management mechanisms do not work because the Compositor
needs to be running before the session can function.

As some session clients support both X11 and Wayland, this command line
option avoids re-writes and fragmentation.

Co-authored-by: @Consolatis

docs/labwc.1.scd

@@ -56,6 +56,19 @@ the `--exit` and `--reconfigure` options use.
 *-s, --startup* <command>
 	Run command on startup
 
+*-S, --session* <command>
+	Run command on startup and terminate compositor on exit. This is useful
+	for session management as it allows the session client to terminate
+	labwc by exiting itself. This is a Wayland specific use-case because
+	under X, xinit starts the server and keeps it alive for as long as the
+	session client. Thus either the session client starts the Window
+	Manager, or the Window Manager can be launched independently first. On
+	Wayland, the Compositor is both Display Server and Window Manager, so
+	the described session management mechanisms do not work because the
+	Compositor needs to be running before the session can function.  As some
+	session clients support both X11 and Wayland, this command line option
+	avoids re-writes and fragmentation.
+
 *-v, --version*
 	Show the version number and quit
 

include/common/spawn.h

@@ -4,6 +4,12 @@
 
 #include <sys/types.h>
 
+/**
+ * spawn_primary_client - execute asynchronously
+ * @command: command to be executed
+ */
+pid_t spawn_primary_client(const char *command);
+
 /**
  * spawn_async_no_shell - execute asynchronously
  * @command: command to be executed

include/labwc.h

@@ -348,6 +348,8 @@ struct server {
 
 	struct menu *menu_current;
 	struct wl_list menus;
+
+	pid_t primary_client_pid;
 };
 
 #define LAB_NR_LAYERS (4)

src/common/spawn.c

@@ -25,11 +25,22 @@ reset_signals_and_limits(void)
 	signal(SIGPIPE, SIG_DFL);
 }
 
-static void
+static bool
 set_cloexec(int fd)
 {
 	int flags = fcntl(fd, F_GETFD);
-	fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
+	if (flags == -1) {
+		wlr_log_errno(WLR_ERROR,
+			"Unable to set the CLOEXEC flag: fnctl failed");
+		return false;
+	}
+	flags = flags | FD_CLOEXEC;
+	if (fcntl(fd, F_SETFD, flags) == -1) {
+		wlr_log_errno(WLR_ERROR,
+			"Unable to set the CLOEXEC flag: fnctl failed");
+		return false;
+	}
+	return true;
 }
 
 void
@@ -79,6 +90,41 @@ out:
 	g_strfreev(argv);
 }
 
+pid_t
+spawn_primary_client(const char *command)
+{
+	assert(command);
+
+	GError *err = NULL;
+	gchar **argv = NULL;
+
+	/* Use glib's shell-parse to mimic Openbox's behaviour */
+	g_shell_parse_argv((gchar *)command, NULL, &argv, &err);
+	if (err) {
+		g_message("%s", err->message);
+		g_error_free(err);
+		return -1;
+	}
+
+	pid_t child = fork();
+	switch (child) {
+	case -1:
+		wlr_log_errno(WLR_ERROR, "Failed to fork");
+		g_strfreev(argv);
+		return -1;
+	case 0:
+		/* child */
+		close(STDIN_FILENO);
+		reset_signals_and_limits();
+		execvp(argv[0], argv);
+		wlr_log_errno(WLR_ERROR, "Failed to execute primary client %s", command);
+		_exit(1);
+	default:
+		g_strfreev(argv);
+		return child;
+	}
+}
+
 pid_t
 spawn_piped(const char *command, int *pipe_fd)
 {

src/main.c

@@ -24,6 +24,7 @@ static const struct option long_options[] = {
 	{"merge-config", no_argument, NULL, 'm'},
 	{"reconfigure", no_argument, NULL, 'r'},
 	{"startup", required_argument, NULL, 's'},
+	{"session", required_argument, NULL, 'S'},
 	{"version", no_argument, NULL, 'v'},
 	{"verbose", no_argument, NULL, 'V'},
 	{0, 0, 0, 0}
@@ -39,6 +40,7 @@ static const char labwc_usage[] =
 "  -m, --merge-config       Merge user config files/theme in all XDG Base Dirs\n"
 "  -r, --reconfigure        Reload the compositor configuration\n"
 "  -s, --startup <command>  Run command on startup\n"
+"  -S, --session <command>  Run command on startup and terminate on exit\n"
 "  -v, --version            Show version number and quit\n"
 "  -V, --verbose            Enable more verbose logging\n";
 
@@ -87,12 +89,13 @@ main(int argc, char *argv[])
 	textdomain(GETTEXT_PACKAGE);
 #endif
 	char *startup_cmd = NULL;
+	char *primary_client = NULL;
 	enum wlr_log_importance verbosity = WLR_ERROR;
 
 	int c;
 	while (1) {
 		int index = 0;
-		c = getopt_long(argc, argv, "c:C:dehmrs:vV", long_options, &index);
+		c = getopt_long(argc, argv, "c:C:dehmrs:S:vV", long_options, &index);
 		if (c == -1) {
 			break;
 		}
@@ -118,6 +121,9 @@ main(int argc, char *argv[])
 		case 's':
 			startup_cmd = optarg;
 			break;
+		case 'S':
+			primary_client = optarg;
+			break;
 		case 'v':
 			printf("labwc " LABWC_VERSION "\n");
 			exit(0);
@@ -171,6 +177,16 @@ main(int argc, char *argv[])
 
 	menu_init(&server);
 
+	/* Start session-manager if one is specified by -S|--session */
+	if (primary_client) {
+		server.primary_client_pid = spawn_primary_client(primary_client);
+		if (server.primary_client_pid < 0) {
+			wlr_log(WLR_ERROR, "fatal error starting primary client: %s",
+				primary_client);
+			goto out;
+		}
+	}
+
 	session_autostart_init(&server);
 	if (startup_cmd) {
 		spawn_async_no_shell(startup_cmd);
@@ -178,6 +194,7 @@ main(int argc, char *argv[])
 
 	wl_display_run(server.wl_display);
 
+out:
 	session_shutdown(&server);
 
 	server_finish(&server);

src/server.c

@@ -90,6 +90,7 @@ handle_sigchld(int signal, void *data)
 {
 	siginfo_t info;
 	info.si_pid = 0;
+	struct server *server = data;
 
 	/* First call waitid() with NOWAIT which doesn't consume the zombie */
 	if (waitid(P_ALL, /*id*/ 0, &info, WEXITED | WNOHANG | WNOWAIT) == -1) {
@@ -102,8 +103,7 @@ handle_sigchld(int signal, void *data)
 	}
 
 #if HAVE_XWAYLAND
-	/* Verify that we do not break xwayland lazy initialization */
-	struct server *server = data;
+	/* Ensure that we do not break xwayland lazy initialization */
 	if (server->xwayland && server->xwayland->server
 			&& info.si_pid == server->xwayland->server->pid) {
 		return 0;
@@ -139,6 +139,11 @@ handle_sigchld(int signal, void *data)
 			" please report", (long)info.si_pid, info.si_code);
 	}
 
+	if (info.si_pid == server->primary_client_pid) {
+		wlr_log(WLR_INFO, "primary client %ld exited", (long)info.si_pid);
+		wl_display_terminate(server->wl_display);
+	}
+
 	return 0;
 }
 
@@ -290,6 +295,7 @@ get_headless_backend(struct wlr_backend *backend, void *data)
 void
 server_init(struct server *server)
 {
+	server->primary_client_pid = -1;
 	server->wl_display = wl_display_create();
 	if (!server->wl_display) {
 		wlr_log(WLR_ERROR, "cannot allocate a wayland display");