xwayland: use pipe instead of SIGUSR1 to signal readiness
Closes: https://github.com/swaywm/wlroots/issues/2154
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@ -22,7 +22,7 @@ struct wlr_xwayland_cursor;
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struct wlr_xwayland_server {
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pid_t pid;
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struct wl_client *client;
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struct wl_event_source *sigusr1_source;
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struct wl_event_source *pipe_source;
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int wm_fd[2], wl_fd[2];
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time_t server_start;
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@ -236,9 +236,6 @@ void wlr_xwayland_server_destroy(struct wlr_xwayland_server *server);
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*
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* The server supports a lazy mode in which Xwayland is only started when a
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* client tries to connect.
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*
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* Note: wlr_xwayland will setup a global SIGUSR1 handler on the compositor
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* process.
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*/
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struct wlr_xwayland *wlr_xwayland_create(struct wl_display *wl_display,
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struct wlr_compositor *compositor, bool lazy);
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@ -57,6 +57,7 @@ noreturn static void exec_xwayland(struct wlr_xwayland_server *server) {
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}
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/* Make Xwayland signal us when it's ready */
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/* TODO: can we use -displayfd instead? */
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signal(SIGUSR1, SIG_IGN);
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char *argv[] = {
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@ -139,8 +140,8 @@ static void server_finish_process(struct wlr_xwayland_server *server) {
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wl_list_remove(&server->client_destroy.link);
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wl_client_destroy(server->client);
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}
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if (server->sigusr1_source) {
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wl_event_source_remove(server->sigusr1_source);
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if (server->pipe_source) {
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wl_event_source_remove(server->pipe_source);
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}
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safe_close(server->wl_fd[0]);
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@ -184,8 +185,8 @@ static void handle_client_destroy(struct wl_listener *listener, void *data) {
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struct wlr_xwayland_server *server =
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wl_container_of(listener, server, client_destroy);
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if (server->sigusr1_source) {
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// Xwayland failed to start, let the sigusr1 handler deal with it
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if (server->pipe_source) {
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// Xwayland failed to start, let the readiness handler deal with it
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return;
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}
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@ -219,7 +220,21 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
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wlr_xwayland_server_destroy(server);
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}
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static int xserver_handle_ready(int signal_number, void *data) {
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static int xserver_handle_ready(int fd, uint32_t mask, void *data) {
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// There are three ways in which we can end up here, from server_start:
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// 1. the second fork failed
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// 2. the exec failed
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// 3. Xwayland sent a SIGUSR1
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//
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// All three cases result in a write to the pipe, which triggers us.
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//
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// For the first two cases, the first fork will exit with
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// EXIT_FAILURE, notifying us that startup failed.
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//
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// For the third case, the first fork will exit with EXIT_SUCCESS
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// and we'll know that Xwayland started successfully.
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close(fd);
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struct wlr_xwayland_server *server = data;
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int stat_val = -1;
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@ -236,8 +251,8 @@ static int xserver_handle_ready(int signal_number, void *data) {
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}
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wlr_log(WLR_DEBUG, "Xserver is ready");
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wl_event_source_remove(server->sigusr1_source);
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server->sigusr1_source = NULL;
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wl_event_source_remove(server->pipe_source);
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server->pipe_source = NULL;
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struct wlr_xwayland_server_ready_event event = {
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.server = server,
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@ -310,19 +325,33 @@ static bool server_start(struct wlr_xwayland_server *server) {
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server->client_destroy.notify = handle_client_destroy;
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wl_client_add_destroy_listener(server->client, &server->client_destroy);
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int p[2];
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if (pipe(p) == -1) {
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wlr_log_errno(WLR_ERROR, "pipe failed");
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server_finish_process(server);
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return false;
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}
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if (!set_cloexec(p[1], true) || !set_cloexec(p[0], true)) {
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wlr_log(WLR_ERROR, "Failed to set CLOEXEC on FD");
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server_finish_process(server);
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return false;
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}
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struct wl_event_loop *loop = wl_display_get_event_loop(server->wl_display);
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server->sigusr1_source = wl_event_loop_add_signal(loop, SIGUSR1,
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xserver_handle_ready, server);
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server->pipe_source = wl_event_loop_add_fd(loop, p[0],
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WL_EVENT_READABLE, xserver_handle_ready, server);
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server->pid = fork();
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if (server->pid < 0) {
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wlr_log_errno(WLR_ERROR, "fork failed");
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close(p[0]);
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close(p[1]);
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server_finish_process(server);
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return false;
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} else if (server->pid == 0) {
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/* Double-fork, but we need to forward SIGUSR1 once Xserver(1)
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* is ready, or error if there was one. */
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pid_t ppid = getppid();
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close(p[0]);
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sigset_t sigset;
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sigemptyset(&sigset);
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sigaddset(&sigset, SIGUSR1);
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@ -332,6 +361,7 @@ static bool server_start(struct wlr_xwayland_server *server) {
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pid_t pid = fork();
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if (pid < 0) {
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wlr_log_errno(WLR_ERROR, "second fork failed");
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(void)!write(p[1], "\n", 1);
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_exit(EXIT_FAILURE);
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} else if (pid == 0) {
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exec_xwayland(server);
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@ -339,8 +369,16 @@ static bool server_start(struct wlr_xwayland_server *server) {
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int sig;
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sigwait(&sigset, &sig);
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kill(ppid, SIGUSR1);
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wlr_log(WLR_DEBUG, "sent SIGUSR1 to process %d", ppid);
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if (write(p[1], "\n", 1) < 1) {
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// Note: if this write failed and we've leaked the write
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// end of the pipe (due to a race between another thread
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// exec'ing and our call to fcntl), then our handler will
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// never wake up and never notice this failure. Hopefully
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// that combination of events is extremely unlikely. This
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// applies to the other write, too.
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wlr_log_errno(WLR_ERROR, "write to pipe failed");
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_exit(EXIT_FAILURE);
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}
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if (sig == SIGCHLD) {
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waitpid(pid, NULL, 0);
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_exit(EXIT_FAILURE);
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@ -351,6 +389,7 @@ static bool server_start(struct wlr_xwayland_server *server) {
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/* close child fds */
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/* remain managing x sockets for lazy start */
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close(p[1]);
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close(server->wl_fd[1]);
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safe_close(server->wm_fd[1]);
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server->wl_fd[1] = server->wm_fd[1] = -1;
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