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xwayland: use pipe instead of SIGUSR1 to signal readiness

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Closes: https://github.com/swaywm/wlroots/issues/2154
This commit is contained in:
Dominik Honnef 2020-11-30 20:41:35 +01:00 committed by Simon Ser
parent 325cba6414
commit 431ec52b9c
2 changed files with 52 additions and 16 deletions
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5
include/wlr/xwayland.h
View file

@ -22,7 +22,7 @@ struct wlr_xwayland_cursor;
struct wlr_xwayland_server {
pid_t pid;
struct wl_client *client;
struct wl_event_source *sigusr1_source;
struct wl_event_source *pipe_source;
int wm_fd[2], wl_fd[2];
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
* 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_compositor *compositor, bool lazy);

63
xwayland/server.c
View file

@ -57,6 +57,7 @@ noreturn static void exec_xwayland(struct wlr_xwayland_server *server) {
}
/* Make Xwayland signal us when it's ready */
/* TODO: can we use -displayfd instead? */
signal(SIGUSR1, SIG_IGN);
char *argv[] = {
@ -139,8 +140,8 @@ static void server_finish_process(struct wlr_xwayland_server *server) {
wl_list_remove(&server->client_destroy.link);
wl_client_destroy(server->client);
}
if (server->sigusr1_source) {
wl_event_source_remove(server->sigusr1_source);
if (server->pipe_source) {
wl_event_source_remove(server->pipe_source);
}
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 =
wl_container_of(listener, server, client_destroy);
if (server->sigusr1_source) {
// Xwayland failed to start, let the sigusr1 handler deal with it
if (server->pipe_source) {
// Xwayland failed to start, let the readiness handler deal with it
return;
}
@ -219,7 +220,21 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
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;
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");
wl_event_source_remove(server->sigusr1_source);
server->sigusr1_source = NULL;
wl_event_source_remove(server->pipe_source);
server->pipe_source = NULL;
struct wlr_xwayland_server_ready_event event = {
.server = server,
@ -310,19 +325,33 @@ static bool server_start(struct wlr_xwayland_server *server) {
server->client_destroy.notify = handle_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);
server->sigusr1_source = wl_event_loop_add_signal(loop, SIGUSR1,
xserver_handle_ready, server);
server->pipe_source = wl_event_loop_add_fd(loop, p[0],
WL_EVENT_READABLE, xserver_handle_ready, server);
server->pid = fork();
if (server->pid < 0) {
wlr_log_errno(WLR_ERROR, "fork failed");
close(p[0]);
close(p[1]);
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();
close(p[0]);
sigset_t sigset;
sigemptyset(&sigset);
sigaddset(&sigset, SIGUSR1);
@ -332,6 +361,7 @@ static bool server_start(struct wlr_xwayland_server *server) {
pid_t pid = fork();
if (pid < 0) {
wlr_log_errno(WLR_ERROR, "second fork failed");
(void)!write(p[1], "\n", 1);
_exit(EXIT_FAILURE);
} else if (pid == 0) {
exec_xwayland(server);
@ -339,8 +369,16 @@ static bool server_start(struct wlr_xwayland_server *server) {
int sig;
sigwait(&sigset, &sig);
kill(ppid, SIGUSR1);
wlr_log(WLR_DEBUG, "sent SIGUSR1 to process %d", ppid);
if (write(p[1], "\n", 1) < 1) {
// 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) {
waitpid(pid, NULL, 0);
_exit(EXIT_FAILURE);
@ -351,6 +389,7 @@ static bool server_start(struct wlr_xwayland_server *server) {
/* close child fds */
/* remain managing x sockets for lazy start */
close(p[1]);
close(server->wl_fd[1]);
safe_close(server->wm_fd[1]);
server->wl_fd[1] = server->wm_fd[1] = -1;