xwayland: Fix infinite loop at startup

Mutter recently added headless tests, and when running those tests the
Wayland compositor runs for a very short time.

Xwayland is spawned by the Wayland compositor and upon startup will
query the various Wayland protocol supported by the compositor.

To do so, it will do a roundtrip to the Wayland server waiting for
events it expects.

If the Wayland compositor terminates before Xwayland has got the replies
it expects, it will loop indefinitely calling `wl_display_roundtrip()`
continuously.

To avoid that issue, add a new `xwl_screen_roundtrip()` that checks for
the returned value from `wl_display_roundtrip()` and fails if it is
negative.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Roman Gilg <subdiff@gmail.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>

(cherry picked from commit 785e59060c00129e47da6c0877604a56d7e0e32f)

3 files changed, 18 insertions, 14 deletions

diff --git a/hw/xwayland/xwayland-input.c b/hw/xwayland/xwayland-input.c
index fa46ac3e7..ba2febc1d 100644
--- a/hw/xwayland/xwayland-input.c
+++ b/hw/xwayland/xwayland-input.c
@@ -2904,9 +2904,7 @@ InitInput(int argc, char *argv[])
     xwl_screen->XYToWindow = pScreen->XYToWindow;
     pScreen->XYToWindow = xwl_xy_to_window;
 
-    wl_display_roundtrip(xwl_screen->display);
-    while (xwl_screen->expecting_event)
-        wl_display_roundtrip(xwl_screen->display);
+    xwl_screen_roundtrip(xwl_screen);
 }
 
 void
diff --git a/hw/xwayland/xwayland.c b/hw/xwayland/xwayland.c
index ed9f2e3c2..44d1bb4da 100644
--- a/hw/xwayland/xwayland.c
+++ b/hw/xwayland/xwayland.c
@@ -1043,6 +1043,19 @@ xwl_sync_events (struct xwl_screen *xwl_screen)
     xwl_read_events (xwl_screen);
 }
 
+void
+xwl_screen_roundtrip(struct xwl_screen *xwl_screen)
+{
+    int ret;
+
+    ret = wl_display_roundtrip(xwl_screen->display);
+    while (ret >= 0 && xwl_screen->expecting_event)
+        ret = wl_display_roundtrip(xwl_screen->display);
+
+    if (ret < 0)
+        xwl_give_up("could not connect to wayland server\n");
+}
+
 static CARD32
 add_client_fd(OsTimerPtr timer, CARD32 time, void *arg)
 {
@@ -1182,14 +1195,7 @@ xwl_screen_init(ScreenPtr pScreen, int argc, char **argv)
     xwl_screen->registry = wl_display_get_registry(xwl_screen->display);
     wl_registry_add_listener(xwl_screen->registry,
                              &registry_listener, xwl_screen);
-    ret = wl_display_roundtrip(xwl_screen->display);
-    if (ret == -1) {
-        ErrorF("could not connect to wayland server\n");
-        return FALSE;
-    }
-
-    while (xwl_screen->expecting_event > 0)
-        wl_display_roundtrip(xwl_screen->display);
+    xwl_screen_roundtrip(xwl_screen);
 
     bpc = xwl_screen->depth / 3;
     green_bpc = xwl_screen->depth - 2 * bpc;
@@ -1281,9 +1287,7 @@ xwl_screen_init(ScreenPtr pScreen, int argc, char **argv)
 
     AddCallback(&PropertyStateCallback, xwl_property_callback, pScreen);
 
-    wl_display_roundtrip(xwl_screen->display);
-    while (xwl_screen->expecting_event)
-        wl_display_roundtrip(xwl_screen->display);
+    xwl_screen_roundtrip(xwl_screen);
 
     return ret;
 }
diff --git a/hw/xwayland/xwayland.h b/hw/xwayland/xwayland.h
index daa719209..bc5836ec4 100644
--- a/hw/xwayland/xwayland.h
+++ b/hw/xwayland/xwayland.h
@@ -381,6 +381,8 @@ void xwl_window_create_frame_callback(struct xwl_window *xwl_window);
 
 void xwl_sync_events (struct xwl_screen *xwl_screen);
 
+void xwl_screen_roundtrip (struct xwl_screen *xwl_screen);
+
 Bool xwl_screen_init_cursor(struct xwl_screen *xwl_screen);
 
 struct xwl_screen *xwl_screen_get(ScreenPtr screen);