xwayland: use pipe instead of SIGUSR1 to signal readiness

Closes: https://github.com/swaywm/wlroots/issues/2154
master
Dominik Honnef 4 years ago committed by Simon Ser
parent 325cba6414
commit 431ec52b9c

@ -22,7 +22,7 @@ struct wlr_xwayland_cursor;
struct wlr_xwayland_server { struct wlr_xwayland_server {
pid_t pid; pid_t pid;
struct wl_client *client; struct wl_client *client;
struct wl_event_source *sigusr1_source; struct wl_event_source *pipe_source;
int wm_fd[2], wl_fd[2]; int wm_fd[2], wl_fd[2];
time_t server_start; time_t server_start;
@ -236,9 +236,6 @@ void wlr_xwayland_server_destroy(struct wlr_xwayland_server *server);
* *
* The server supports a lazy mode in which Xwayland is only started when a * The server supports a lazy mode in which Xwayland is only started when a
* client tries to connect. * client tries to connect.
*
* Note: wlr_xwayland will setup a global SIGUSR1 handler on the compositor
* process.
*/ */
struct wlr_xwayland *wlr_xwayland_create(struct wl_display *wl_display, struct wlr_xwayland *wlr_xwayland_create(struct wl_display *wl_display,
struct wlr_compositor *compositor, bool lazy); struct wlr_compositor *compositor, bool lazy);

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

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