xwayland: split server

Split the server part of wlr_xwayland into wlr_xwayland_server. This
allows compositors to implement their own XWM when wlroots' isn't a good
fit.

1 files changed, 400 insertions, 0 deletions

diff --git a/xwayland/server.c b/xwayland/server.c
new file mode 100644
index 00000000..0c76a389
--- /dev/null
+++ b/xwayland/server.c
@@ -0,0 +1,400 @@
+#define _POSIX_C_SOURCE 200809L
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdlib.h>
+#include <stdnoreturn.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+#include <wayland-server-core.h>
+#include <wlr/util/log.h>
+#include <wlr/xwayland.h>
+#include "sockets.h"
+#include "util/signal.h"
+
+static void safe_close(int fd) {
+	if (fd >= 0) {
+		close(fd);
+	}
+}
+
+static int fill_arg(char ***argv, const char *fmt, ...) {
+	int len;
+	char **cur_arg = *argv;
+	va_list args;
+	va_start(args, fmt);
+	len = vsnprintf(NULL, 0, fmt, args) + 1;
+	va_end(args);
+	while (*cur_arg) {
+		cur_arg++;
+	}
+	*cur_arg = malloc(len);
+	if (!*cur_arg) {
+		return -1;
+	}
+	*argv = cur_arg;
+	va_start(args, fmt);
+	len = vsnprintf(*cur_arg, len, fmt, args);
+	va_end(args);
+	return len;
+}
+
+noreturn static void exec_xwayland(struct wlr_xwayland_server *server) {
+	if (!set_cloexec(server->x_fd[0], false) ||
+			!set_cloexec(server->x_fd[1], false) ||
+			!set_cloexec(server->wm_fd[1], false) ||
+			!set_cloexec(server->wl_fd[1], false)) {
+		_exit(EXIT_FAILURE);
+	}
+
+	/* Make Xwayland signal us when it's ready */
+	signal(SIGUSR1, SIG_IGN);
+
+	char *argv[] = {
+		"Xwayland", NULL /* display, e.g. :1 */,
+		"-rootless", "-terminate",
+		"-listen", NULL /* x_fd[0] */,
+		"-listen", NULL /* x_fd[1] */,
+		"-wm", NULL /* wm_fd[1] */,
+		NULL,
+	};
+	char **cur_arg = argv;
+
+	if (fill_arg(&cur_arg, ":%d", server->display) < 0 ||
+			fill_arg(&cur_arg, "%d", server->x_fd[0]) < 0 ||
+			fill_arg(&cur_arg, "%d", server->x_fd[1]) < 0 ||
+			fill_arg(&cur_arg, "%d", server->wm_fd[1]) < 0) {
+		wlr_log_errno(WLR_ERROR, "alloc/print failure");
+		_exit(EXIT_FAILURE);
+	}
+
+	char wayland_socket_str[16];
+	snprintf(wayland_socket_str, sizeof(wayland_socket_str), "%d", server->wl_fd[1]);
+	setenv("WAYLAND_SOCKET", wayland_socket_str, true);
+
+	wlr_log(WLR_INFO, "WAYLAND_SOCKET=%d Xwayland :%d -rootless -terminate -listen %d -listen %d -wm %d",
+		server->wl_fd[1], server->display, server->x_fd[0],
+		server->x_fd[1], server->wm_fd[1]);
+
+	// Closes stdout/stderr depending on log verbosity
+	enum wlr_log_importance verbosity = wlr_log_get_verbosity();
+	int devnull = open("/dev/null", O_WRONLY | O_CREAT | O_CLOEXEC, 0666);
+	if (devnull < 0) {
+		wlr_log_errno(WLR_ERROR, "XWayland: failed to open /dev/null");
+		_exit(EXIT_FAILURE);
+	}
+	if (verbosity < WLR_INFO) {
+		dup2(devnull, STDOUT_FILENO);
+	}
+	if (verbosity < WLR_ERROR) {
+		dup2(devnull, STDERR_FILENO);
+	}
+
+	// This returns if and only if the call fails
+	execvp("Xwayland", argv);
+
+	wlr_log_errno(WLR_ERROR, "failed to exec Xwayland");
+	close(devnull);
+	_exit(EXIT_FAILURE);
+}
+
+static void server_finish_process(struct wlr_xwayland_server *server) {
+	if (!server || server->display == -1) {
+		return;
+	}
+
+	if (server->x_fd_read_event[0]) {
+		wl_event_source_remove(server->x_fd_read_event[0]);
+		wl_event_source_remove(server->x_fd_read_event[1]);
+
+		server->x_fd_read_event[0] = server->x_fd_read_event[1] = NULL;
+	}
+
+	if (server->client) {
+		wl_list_remove(&server->client_destroy.link);
+		wl_client_destroy(server->client);
+	}
+	if (server->sigusr1_source) {
+		wl_event_source_remove(server->sigusr1_source);
+	}
+
+	safe_close(server->wl_fd[0]);
+	safe_close(server->wl_fd[1]);
+	safe_close(server->wm_fd[0]);
+	safe_close(server->wm_fd[1]);
+	memset(server, 0, offsetof(struct wlr_xwayland_server, display));
+	server->wl_fd[0] = server->wl_fd[1] = -1;
+	server->wm_fd[0] = server->wm_fd[1] = -1;
+
+	/* We do not kill the Xwayland process, it dies to broken pipe
+	 * after we close our side of the wm/wl fds. This is more reliable
+	 * than trying to kill something that might no longer be Xwayland.
+	 */
+}
+
+static void server_finish_display(struct wlr_xwayland_server *server) {
+	if (!server || server->display == -1) {
+		return;
+	}
+
+	safe_close(server->x_fd[0]);
+	safe_close(server->x_fd[1]);
+	server->x_fd[0] = server->x_fd[1] = -1;
+
+	wl_list_remove(&server->display_destroy.link);
+
+	unlink_display_sockets(server->display);
+	server->display = -1;
+	server->display_name[0] = '\0';
+}
+
+static bool server_start(struct wlr_xwayland_server *server);
+static bool server_start_lazy(struct wlr_xwayland_server *server);
+
+static void handle_client_destroy(struct wl_listener *listener, void *data) {
+	struct wlr_xwayland_server *server =
+		wl_container_of(listener, server, client_destroy);
+
+	if (server->sigusr1_source) {
+		// Xwayland failed to start, let the sigusr1 handler deal with it
+		return;
+	}
+
+	// Don't call client destroy: it's being destroyed already
+	server->client = NULL;
+	wl_list_remove(&server->client_destroy.link);
+
+	server_finish_process(server);
+
+	if (time(NULL) - server->server_start > 5) {
+		if (server->lazy) {
+			wlr_log(WLR_INFO, "Restarting Xwayland (lazy)");
+			server_start_lazy(server);
+		} else  {
+			wlr_log(WLR_INFO, "Restarting Xwayland");
+			server_start(server);
+		}
+	}
+}
+
+static void handle_display_destroy(struct wl_listener *listener, void *data) {
+	struct wlr_xwayland_server *server =
+		wl_container_of(listener, server, display_destroy);
+
+	// Don't call client destroy: the display is being destroyed, it's too late
+	if (server->client) {
+		server->client = NULL;
+		wl_list_remove(&server->client_destroy.link);
+	}
+
+	wlr_xwayland_server_destroy(server);
+}
+
+static int xserver_handle_ready(int signal_number, void *data) {
+	struct wlr_xwayland_server *server = data;
+
+	int stat_val = -1;
+	while (waitpid(server->pid, &stat_val, 0) < 0) {
+		if (errno == EINTR) {
+			continue;
+		}
+		wlr_log_errno(WLR_ERROR, "waitpid for Xwayland fork failed");
+		goto error;
+	}
+	if (stat_val) {
+		wlr_log(WLR_ERROR, "Xwayland startup failed, not setting up xwm");
+		goto error;
+	}
+	wlr_log(WLR_DEBUG, "Xserver is ready");
+
+	wl_event_source_remove(server->sigusr1_source);
+	server->sigusr1_source = NULL;
+
+	struct wlr_xwayland_server_ready_event event = {
+		.server = server,
+		.wm_fd = server->wm_fd[0],
+	};
+	wlr_signal_emit_safe(&server->events.ready, &event);
+	/* ready is a one-shot signal, fire and forget */
+	wl_signal_init(&server->events.ready);
+
+	return 1; /* wayland event loop dispatcher's count */
+
+error:
+	/* clean up */
+	server_finish_process(server);
+	server_finish_display(server);
+	return 1;
+}
+
+static bool server_start_display(struct wlr_xwayland_server *server,
+		struct wl_display *wl_display) {
+	server->display_destroy.notify = handle_display_destroy;
+	wl_display_add_destroy_listener(wl_display, &server->display_destroy);
+
+	server->display = open_display_sockets(server->x_fd);
+	if (server->display < 0) {
+		server_finish_display(server);
+		return false;
+	}
+
+	snprintf(server->display_name, sizeof(server->display_name),
+		":%d", server->display);
+	return true;
+}
+
+static bool server_start(struct wlr_xwayland_server *server) {
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, server->wl_fd) != 0 ||
+			socketpair(AF_UNIX, SOCK_STREAM, 0, server->wm_fd) != 0) {
+		wlr_log_errno(WLR_ERROR, "socketpair failed");
+		server_finish_process(server);
+		return false;
+	}
+	if (!set_cloexec(server->wl_fd[0], true) ||
+			!set_cloexec(server->wl_fd[1], true) ||
+			!set_cloexec(server->wm_fd[0], true) ||
+			!set_cloexec(server->wm_fd[1], true)) {
+		server_finish_process(server);
+		return false;
+	}
+
+	server->server_start = time(NULL);
+
+	server->client = wl_client_create(server->wl_display, server->wl_fd[0]);
+	if (!server->client) {
+		wlr_log_errno(WLR_ERROR, "wl_client_create failed");
+		server_finish_process(server);
+		return false;
+	}
+
+	server->wl_fd[0] = -1; /* not ours anymore */
+
+	server->client_destroy.notify = handle_client_destroy;
+	wl_client_add_destroy_listener(server->client, &server->client_destroy);
+
+	struct wl_event_loop *loop = wl_display_get_event_loop(server->wl_display);
+	server->sigusr1_source = wl_event_loop_add_signal(loop, SIGUSR1,
+		xserver_handle_ready, server);
+
+	server->pid = fork();
+	if (server->pid < 0) {
+		wlr_log_errno(WLR_ERROR, "fork failed");
+		server_finish_process(server);
+		return false;
+	} else if (server->pid == 0) {
+		/* Double-fork, but we need to forward SIGUSR1 once Xserver(1)
+		 * is ready, or error if there was one. */
+		pid_t ppid = getppid();
+		sigset_t sigset;
+		sigemptyset(&sigset);
+		sigaddset(&sigset, SIGUSR1);
+		sigaddset(&sigset, SIGCHLD);
+		sigprocmask(SIG_BLOCK, &sigset, NULL);
+
+		pid_t pid = fork();
+		if (pid < 0) {
+			wlr_log_errno(WLR_ERROR, "second fork failed");
+			_exit(EXIT_FAILURE);
+		} else if (pid == 0) {
+			exec_xwayland(server);
+		}
+
+		int sig;
+		sigwait(&sigset, &sig);
+		kill(ppid, SIGUSR1);
+		wlr_log(WLR_DEBUG, "sent SIGUSR1 to process %d", ppid);
+		if (sig == SIGCHLD) {
+			waitpid(pid, NULL, 0);
+			_exit(EXIT_FAILURE);
+		}
+
+		_exit(EXIT_SUCCESS);
+	}
+
+	/* close child fds */
+	/* remain managing x sockets for lazy start */
+	close(server->wl_fd[1]);
+	close(server->wm_fd[1]);
+	server->wl_fd[1] = server->wm_fd[1] = -1;
+
+	return true;
+}
+
+static int xwayland_socket_connected(int fd, uint32_t mask, void *data) {
+	struct wlr_xwayland_server *server = data;
+
+	wl_event_source_remove(server->x_fd_read_event[0]);
+	wl_event_source_remove(server->x_fd_read_event[1]);
+	server->x_fd_read_event[0] = server->x_fd_read_event[1] = NULL;
+
+	server_start(server);
+
+	return 0;
+}
+
+static bool server_start_lazy(struct wlr_xwayland_server *server) {
+	struct wl_event_loop *loop = wl_display_get_event_loop(server->wl_display);
+	server->x_fd_read_event[0] = wl_event_loop_add_fd(loop, server->x_fd[0],
+		WL_EVENT_READABLE, xwayland_socket_connected, server);
+	server->x_fd_read_event[1] = wl_event_loop_add_fd(loop, server->x_fd[1],
+		WL_EVENT_READABLE, xwayland_socket_connected, server);
+
+	return true;
+}
+
+void wlr_xwayland_server_destroy(struct wlr_xwayland_server *server) {
+	if (!server) {
+		return;
+	}
+
+	server_finish_process(server);
+	server_finish_display(server);
+	wlr_signal_emit_safe(&server->events.destroy, NULL);
+	free(server);
+}
+
+struct wlr_xwayland_server *wlr_xwayland_server_create(
+		struct wl_display *wl_display, bool lazy) {
+	struct wlr_xwayland_server *server =
+		calloc(1, sizeof(struct wlr_xwayland_server));
+	if (!server) {
+		return NULL;
+	}
+
+	server->wl_display = wl_display;
+	server->lazy = lazy;
+
+	server->x_fd[0] = server->x_fd[1] = -1;
+	server->wl_fd[0] = server->wl_fd[1] = -1;
+	server->wm_fd[0] = server->wm_fd[1] = -1;
+
+	wl_signal_init(&server->events.ready);
+	wl_signal_init(&server->events.destroy);
+
+	if (!server_start_display(server, wl_display)) {
+		goto error_alloc;
+	}
+
+	if (server->lazy) {
+		if (!server_start_lazy(server)) {
+			goto error_display;
+		}
+	} else {
+		if (!server_start(server)) {
+			goto error_display;
+		}
+	}
+
+	return server;
+
+error_display:
+	server_finish_display(server);
+error_alloc:
+	free(server);
+	return NULL;
+}