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xwayland: use -displayfd instead of USR1 to signal readiness 

We want to wait for Xwayland to be ready before issuing it blocking
requests, but relying on USR1 is a bit unsafe:
 - we can't ascertain the signal originated from Xwayland
 - if weston is started as PID1 (e.g. in its own container), then
   Xwayland will not send SIGUSR1 and X11 connections will be stuck
   forever: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1312

Creating a pipe and using -displayfd, even if we don't care about the
display value itself, is safe and works for all cases

Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
This commit is contained in:
Dominique Martinet 2022-04-11 19:52:27 +09:00 committed by Marius Vlad
parent e1a111e1b7
commit c2f4201ed2
1 changed files with 53 additions and 26 deletions
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79
compositor/xwayland.c
View File

@ -35,6 +35,7 @@
#include "compositor/weston.h"
#include <libweston/xwayland-api.h>
#include "shared/helpers.h"
#include "shared/os-compatibility.h"
#ifdef HAVE_XWAYLAND_LISTENFD
# define LISTEN_STR "-listenfd"
@ -46,24 +47,44 @@ struct wet_xwayland {
struct weston_compositor *compositor;
const struct weston_xwayland_api *api;
struct weston_xwayland *xwayland;
struct wl_event_source *sigusr1_source;
struct wl_event_source *display_fd_source;
struct wl_client *client;
int wm_fd;
struct weston_process process;
};
static int
handle_sigusr1(int signal_number, void *data)
handle_display_fd(int fd, uint32_t mask, void *data)
{
struct wet_xwayland *wxw = data;
char buf[64];
ssize_t n;
/* xwayland exited before being ready, don't finish initialization,
* the process watcher will cleanup */
if (!(mask & WL_EVENT_READABLE))
goto out;
/* Xwayland writes to the pipe twice, so if we close it too early
* it's possible the second write will fail and Xwayland shuts down.
* Make sure we read until end of line marker to avoid this. */
n = read(fd, buf, sizeof buf);
if (n < 0 && errno != EAGAIN) {
weston_log("read from Xwayland display_fd failed: %s\n",
strerror(errno));
goto out;
}
/* Returning 1 here means recheck and call us again if required. */
if (n <= 0 || (n > 0 && buf[n - 1] != '\n'))
return 1;
/* We'd be safer if we actually had the struct
* signalfd_siginfo from the signalfd data and could verify
* this came from Xwayland.*/
wxw->api->xserver_loaded(wxw->xwayland, wxw->client, wxw->wm_fd);
wl_event_source_remove(wxw->sigusr1_source);
return 1;
out:
wl_event_source_remove(wxw->display_fd_source);
close(fd);
return 0;
}
static pid_t
@ -72,10 +93,12 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
struct wet_xwayland *wxw = user_data;
pid_t pid;
char s[12], abstract_fd_str[12], unix_fd_str[12], wm_fd_str[12];
int sv[2], wm[2], fd;
char display_fd_str[12];
int sv[2], wm[2], fd, display_fd[2];
char *xserver = NULL;
struct weston_config *config = wet_get_config(wxw->compositor);
struct weston_config_section *section;
struct wl_event_loop *loop;
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sv) < 0) {
weston_log("wl connection socketpair failed\n");
@ -87,6 +110,16 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
return 1;
}
if (pipe(display_fd) < 0) {
weston_log("pipe creation for displayfd failed\n");
return 1;
}
if (os_fd_set_cloexec(display_fd[0]) != 0) {
weston_log("failed setting remaining end of displayfd as cloexec\n");
return 1;
}
pid = fork();
switch (pid) {
case 0:
@ -110,27 +143,20 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
if (fd < 0)
goto fail;
snprintf(wm_fd_str, sizeof wm_fd_str, "%d", fd);
snprintf(display_fd_str, sizeof display_fd_str, "%d", display_fd[1]);
section = weston_config_get_section(config,
"xwayland", NULL, NULL);
weston_config_section_get_string(section, "path",
&xserver, XSERVER_PATH);
/* Ignore SIGUSR1 in the child, which will make the X
* server send SIGUSR1 to the parent (weston) when
* it's done with initialization. During
* initialization the X server will round trip and
* block on the wayland compositor, so avoid making
* blocking requests (like xcb_connect_to_fd) until
* it's done with that. */
signal(SIGUSR1, SIG_IGN);
if (execl(xserver,
xserver,
display,
"-rootless",
LISTEN_STR, abstract_fd_str,
LISTEN_STR, unix_fd_str,
"-displayfd", display_fd_str,
"-wm", wm_fd_str,
"-terminate",
NULL) < 0)
@ -150,6 +176,16 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
close(wm[1]);
wxw->wm_fd = wm[0];
/* During initialization the X server will round trip
* and block on the wayland compositor, so avoid making
* blocking requests (like xcb_connect_to_fd) until
* it's done with that. */
close(display_fd[1]);
loop = wl_display_get_event_loop(wxw->compositor->wl_display);
wxw->display_fd_source =
wl_event_loop_add_fd(loop, display_fd[0], WL_EVENT_READABLE,
handle_display_fd, wxw);
wxw->process.pid = pid;
wet_watch_process(wxw->compositor, &wxw->process);
break;
@ -167,12 +203,8 @@ xserver_cleanup(struct weston_process *process, int status)
{
struct wet_xwayland *wxw =
container_of(process, struct wet_xwayland, process);
struct wl_event_loop *loop =
wl_display_get_event_loop(wxw->compositor->wl_display);
wxw->api->xserver_exited(wxw->xwayland, status);
wxw->sigusr1_source = wl_event_loop_add_signal(loop, SIGUSR1,
handle_sigusr1, wxw);
wxw->client = NULL;
}
@ -182,7 +214,6 @@ wet_load_xwayland(struct weston_compositor *comp)
const struct weston_xwayland_api *api;
struct weston_xwayland *xwayland;
struct wet_xwayland *wxw;
struct wl_event_loop *loop;
if (weston_compositor_load_xwayland(comp) < 0)
return -1;
@ -210,9 +241,5 @@ wet_load_xwayland(struct weston_compositor *comp)
if (api->listen(xwayland, wxw, spawn_xserver) < 0)
return -1;
loop = wl_display_get_event_loop(comp->wl_display);
wxw->sigusr1_source = wl_event_loop_add_signal(loop, SIGUSR1,
handle_sigusr1, wxw);
return 0;
}