xwayland: try flushing immediately in xwm_schedule_flush()

wl_event_source_fd_update() goes through another event loop cycle, which
delays writes. This extra cycle was introduced in 6ada67da9b
("xwayland/xwm: implement somewhat asynchronous request flushing").

Try flushing the X11 WM FD immediately if we can.

References: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/4044

include/wlr/types/wlr_cursor.h

@@ -49,30 +49,30 @@ struct wlr_cursor {
 	 * your responsibility.
 	 */
 	struct {
-		struct wl_signal motion;
-		struct wl_signal motion_absolute;
-		struct wl_signal button;
-		struct wl_signal axis;
+		struct wl_signal motion; // struct wlr_pointer_motion_event
+		struct wl_signal motion_absolute; // struct wlr_pointer_motion_absolute_event
+		struct wl_signal button; // struct wlr_pointer_button_event
+		struct wl_signal axis; // struct wlr_pointer_axis_event
 		struct wl_signal frame;
-		struct wl_signal swipe_begin;
-		struct wl_signal swipe_update;
-		struct wl_signal swipe_end;
-		struct wl_signal pinch_begin;
-		struct wl_signal pinch_update;
-		struct wl_signal pinch_end;
-		struct wl_signal hold_begin;
-		struct wl_signal hold_end;
+		struct wl_signal swipe_begin; // struct wlr_pointer_swipe_begin_event
+		struct wl_signal swipe_update; // struct wlr_pointer_swipe_update_event
+		struct wl_signal swipe_end; // struct wlr_pointer_swipe_end_event
+		struct wl_signal pinch_begin; // struct wlr_pointer_pinch_begin_event
+		struct wl_signal pinch_update; // struct wlr_pointer_pinch_update_event
+		struct wl_signal pinch_end; // struct wlr_pointer_pinch_end_event
+		struct wl_signal hold_begin; // struct wlr_pointer_hold_begin_event
+		struct wl_signal hold_end; // struct wlr_pointer_hold_end_event
 
-		struct wl_signal touch_up;
-		struct wl_signal touch_down;
-		struct wl_signal touch_motion;
-		struct wl_signal touch_cancel;
+		struct wl_signal touch_up; // struct wlr_touch_up_event
+		struct wl_signal touch_down; // struct wlr_touch_down_event
+		struct wl_signal touch_motion; // struct wlr_touch_motion_event
+		struct wl_signal touch_cancel; // struct wlr_touch_cancel_event
 		struct wl_signal touch_frame;
 
-		struct wl_signal tablet_tool_axis;
-		struct wl_signal tablet_tool_proximity;
-		struct wl_signal tablet_tool_tip;
-		struct wl_signal tablet_tool_button;
+		struct wl_signal tablet_tool_axis; // struct wlr_tablet_tool_axis_event
+		struct wl_signal tablet_tool_proximity; // struct wlr_tablet_tool_proximity_event
+		struct wl_signal tablet_tool_tip; // struct wlr_tablet_tool_tip_event
+		struct wl_signal tablet_tool_button; // struct wlr_tablet_tool_button_event
 	} events;
 
 	void *data;

render/drm_syncobj.c

@@ -167,10 +167,9 @@ bool wlr_drm_syncobj_timeline_check(struct wlr_drm_syncobj_timeline *timeline,
 	etime = ETIME;
 #endif
 
-	uint32_t signaled_point;
-	int ret = drmSyncobjTimelineWait(timeline->drm_fd, &timeline->handle, &point, 1, 0, flags, &signaled_point);
+	int ret = drmSyncobjTimelineWait(timeline->drm_fd, &timeline->handle, &point, 1, 0, flags, NULL);
 	if (ret != 0 && ret != -etime) {
-		wlr_log_errno(WLR_ERROR, "drmSyncobjWait() failed");
+		wlr_log_errno(WLR_ERROR, "drmSyncobjTimelineWait() failed");
 		return false;
 	}
 

types/wlr_cursor.c

@@ -956,7 +956,7 @@ static void handle_tablet_tool_axis(struct wl_listener *listener, void *data) {
 
 static void handle_tablet_tool_button(struct wl_listener *listener,
 		void *data) {
-	struct wlr_tablet_tool_button *event = data;
+	struct wlr_tablet_tool_button_event *event = data;
 	struct wlr_cursor_device *device;
 	device = wl_container_of(listener, device, tablet_tool_button);
 	wl_signal_emit_mutable(&device->cursor->events.tablet_tool_button, event);

types/wlr_keyboard_group.c

@@ -308,7 +308,7 @@ void wlr_keyboard_group_remove_keyboard(struct wlr_keyboard_group *group,
 void wlr_keyboard_group_destroy(struct wlr_keyboard_group *group) {
 	struct keyboard_group_device *device, *tmp_device;
 	wl_list_for_each_safe(device, tmp_device, &group->devices, link) {
-		wlr_keyboard_group_remove_keyboard(group, device->keyboard);
+		remove_keyboard_group_device(device);
 	}
 
 	// Now group->keys might not be empty if a wlr_keyboard has emitted

xwayland/xwm.c

@@ -1,5 +1,6 @@
 #include <assert.h>
 #include <drm_fourcc.h>
+#include <poll.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <wlr/types/wlr_buffer.h>
@@ -2881,5 +2882,20 @@ xcb_connection_t *wlr_xwayland_get_xwm_connection(
 }
 
 void xwm_schedule_flush(struct wlr_xwm *xwm) {
+	struct pollfd pollfd = {
+		.fd = xcb_get_file_descriptor(xwm->xcb_conn),
+		.events = POLLOUT,
+	};
+	if (poll(&pollfd, 1, 0) < 0) {
+		wlr_log(WLR_ERROR, "poll() failed");
+		return;
+	}
+
+	// If we can write immediately, do so
+	if (pollfd.revents & POLLOUT) {
+		xcb_flush(xwm->xcb_conn);
+		return;
+	}
+
 	wl_event_source_fd_update(xwm->event_source, WL_EVENT_READABLE | WL_EVENT_WRITABLE);
 }