From 9e85aa9c1fbf51ef00674e3a91aded4083a14a15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michel=20D=C3=A4nzer?= <mdaenzer@redhat.com>
Date: Thu, 30 Jan 2020 12:29:03 +0100
Subject: [PATCH] xwayland/glamor-gbm: Add xwl_glamor_gbm_post_damage hook

It flushes any pending drawing to the kernel, to make sure it'll be
visible to the Wayland server.

Without this, it was possible for the Wayland server to process surface
commits before Xwayland got around to flushing the corresponding
drawing, which could result in stale or even completely random window
contents being visible.

v2:
* Make EGL backend post_damage hook mandatory, don't check for NULL in
  xwl_glamor_post_damage. (Olivier Fourdan)

Closes: https://gitlab.freedesktop.org/xorg/xserver/issues/951
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
---
 hw/xwayland/xwayland-glamor-gbm.c | 10 ++++++++++
 hw/xwayland/xwayland-glamor.c     |  3 +--
 hw/xwayland/xwayland-glamor.h     |  6 ++----
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/hw/xwayland/xwayland-glamor-gbm.c b/hw/xwayland/xwayland-glamor-gbm.c
index 80655fd16..17682a172 100644
--- a/hw/xwayland/xwayland-glamor-gbm.c
+++ b/hw/xwayland/xwayland-glamor-gbm.c
@@ -49,6 +49,7 @@
 #include "xwayland-glamor.h"
 #include "xwayland-pixmap.h"
 #include "xwayland-screen.h"
+#include "xwayland-window.h"
 
 #include "linux-dmabuf-unstable-v1-client-protocol.h"
 
@@ -919,6 +920,14 @@ xwl_glamor_gbm_has_wl_interfaces(struct xwl_screen *xwl_screen)
     return TRUE;
 }
 
+static void
+xwl_glamor_gbm_post_damage(struct xwl_window *xwl_window, PixmapPtr pixmap,
+                           RegionPtr region)
+{
+    /* Make sure any pending drawing to the pixmap is flushed to the kernel */
+    glamor_block_handler(xwl_window->xwl_screen->screen);
+}
+
 static Bool
 xwl_glamor_gbm_init_egl(struct xwl_screen *xwl_screen)
 {
@@ -1111,5 +1120,6 @@ xwl_glamor_init_gbm(struct xwl_screen *xwl_screen)
     xwl_screen->gbm_backend.init_egl = xwl_glamor_gbm_init_egl;
     xwl_screen->gbm_backend.init_screen = xwl_glamor_gbm_init_screen;
     xwl_screen->gbm_backend.get_wl_buffer_for_pixmap = xwl_glamor_gbm_get_wl_buffer_for_pixmap;
+    xwl_screen->gbm_backend.post_damage = xwl_glamor_gbm_post_damage;
     xwl_screen->gbm_backend.is_available = TRUE;
 }
diff --git a/hw/xwayland/xwayland-glamor.c b/hw/xwayland/xwayland-glamor.c
index d9523b0a7..f3327f4ee 100644
--- a/hw/xwayland/xwayland-glamor.c
+++ b/hw/xwayland/xwayland-glamor.c
@@ -124,8 +124,7 @@ xwl_glamor_post_damage(struct xwl_window *xwl_window,
 {
     struct xwl_screen *xwl_screen = xwl_window->xwl_screen;
 
-    if (xwl_screen->egl_backend->post_damage)
-        xwl_screen->egl_backend->post_damage(xwl_window, pixmap, region);
+    xwl_screen->egl_backend->post_damage(xwl_window, pixmap, region);
 }
 
 Bool
diff --git a/hw/xwayland/xwayland-glamor.h b/hw/xwayland/xwayland-glamor.h
index e9896bfef..138accd6d 100644
--- a/hw/xwayland/xwayland-glamor.h
+++ b/hw/xwayland/xwayland-glamor.h
@@ -70,10 +70,8 @@ struct xwl_egl_backend {
                                                   Bool *created);
 
     /* Called by Xwayland to perform any pre-wl_surface damage routines
-     * that are required by the backend. If your backend is poorly
-     * designed and lacks the ability to render directly to a surface,
-     * you should implement blitting from the glamor pixmap to the wayland
-     * pixmap here. Otherwise, this callback is optional.
+     * that are required by the backend to make sure any pending drawing
+     * operations to the pixmap will be visible to the Wayland server.
      */
     void (*post_damage)(struct xwl_window *xwl_window,
                         PixmapPtr pixmap, RegionPtr region);