backend/x11: use DRI3Open to get DRM FD

Instead of relying on EGL to retrieve the DRM FD, query it from the
DRI3 extension.

Use the EGL GBM platform, and drop the EGL config.

backend/x11/backend.c

@@ -180,8 +180,9 @@ static void backend_destroy(struct wlr_backend *backend) {
 	wl_list_remove(&x11->display_destroy.link);
 
 	wlr_renderer_destroy(x11->renderer);
-	wlr_drm_format_set_finish(&x11->dri3_formats);
 	wlr_egl_finish(&x11->egl);
+	wlr_allocator_destroy(x11->allocator);
+	wlr_drm_format_set_finish(&x11->dri3_formats);
 	free(x11->drm_format);
 
 #if WLR_HAS_XCB_ERRORS
@@ -237,6 +238,39 @@ static xcb_visualid_t pick_visualid(xcb_depth_t *depth) {
 	return 0;
 }
 
+static int query_dri3_drm_fd(struct wlr_x11_backend *x11) {
+	xcb_dri3_open_cookie_t open_cookie =
+		xcb_dri3_open(x11->xcb, x11->screen->root, 0);
+	xcb_dri3_open_reply_t *open_reply =
+		xcb_dri3_open_reply(x11->xcb, open_cookie, NULL);
+	if (open_reply == NULL) {
+		return -1;
+	}
+
+	int *open_fds = xcb_dri3_open_reply_fds(x11->xcb, open_reply);
+	if (open_fds == NULL) {
+		free(open_reply);
+		return -1;
+	}
+
+	assert(open_reply->nfd == 1);
+	int drm_fd = open_fds[0];
+
+	free(open_reply);
+
+	int flags = fcntl(drm_fd, F_GETFD);
+	if (flags < 0) {
+		close(drm_fd);
+		return -1;
+	}
+	if (fcntl(drm_fd, F_SETFD, flags | FD_CLOEXEC) < 0) {
+		close(drm_fd);
+		return -1;
+	}
+
+	return drm_fd;
+}
+
 static bool query_dri3_modifiers(struct wlr_x11_backend *x11,
 		const struct wlr_x11_format *format) {
 	// Query the root window's supported modifiers, because we only care about
@@ -437,72 +471,58 @@ struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
 	x11->screen = xcb_setup_roots_iterator(xcb_get_setup(x11->xcb)).data;
 	if (!x11->screen) {
 		wlr_log(WLR_ERROR, "Failed to get X11 screen");
-		goto error_display;
+		goto error_event;
 	}
 
 	x11->depth = get_depth(x11->screen, 32);
 	if (!x11->depth) {
 		wlr_log(WLR_ERROR, "Failed to get 32-bit depth for X11 screen");
-		goto error_display;
+		goto error_event;
 	}
 
 	x11->visualid = pick_visualid(x11->depth);
 	if (!x11->visualid) {
 		wlr_log(WLR_ERROR, "Failed to pick X11 visual");
-		goto error_display;
+		goto error_event;
 	}
 
 	x11->x11_format = x11_format_from_depth(x11->depth->depth);
 	if (!x11->x11_format) {
 		wlr_log(WLR_ERROR, "Unsupported depth %"PRIu8, x11->depth->depth);
-		goto error_display;
+		goto error_event;
 	}
 
 	x11->colormap = xcb_generate_id(x11->xcb);
 	xcb_create_colormap(x11->xcb, XCB_COLORMAP_ALLOC_NONE, x11->colormap,
 		x11->screen->root, x11->visualid);
 
+	// DRI3 may return a render node (Xwayland) or an authenticated primary
+	// node (plain Glamor).
+	int drm_fd = query_dri3_drm_fd(x11);
+	if (drm_fd < 0) {
+		wlr_log(WLR_ERROR, "Failed to query DRI3 DRM FD");
+		goto error_event;
+	}
+
+	struct wlr_gbm_allocator *gbm_alloc = wlr_gbm_allocator_create(drm_fd);
+	if (gbm_alloc == NULL) {
+		wlr_log(WLR_ERROR, "Failed to create GBM allocator");
+		close(drm_fd);
+		goto error_event;
+	}
+	x11->allocator = &gbm_alloc->base;
+
 	if (!create_renderer_func) {
 		create_renderer_func = wlr_renderer_autocreate;
 	}
 
-	static EGLint config_attribs[] = {
+	x11->renderer = create_renderer_func(&x11->egl, EGL_PLATFORM_GBM_KHR,
-		EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
+		gbm_alloc->gbm_device, NULL, 0);
-		EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
-		EGL_RED_SIZE, 1,
-		EGL_GREEN_SIZE, 1,
-		EGL_BLUE_SIZE, 1,
-		EGL_ALPHA_SIZE, 1,
-		EGL_NONE,
-	};
-
-	x11->renderer = create_renderer_func(&x11->egl, EGL_PLATFORM_X11_KHR,
-		x11->xlib_conn, config_attribs, x11->screen->root_visual);
 	if (x11->renderer == NULL) {
 		wlr_log(WLR_ERROR, "Failed to create renderer");
 		goto error_event;
 	}
 
-	// TODO: we can use DRI3Open instead
-	int drm_fd = wlr_renderer_get_drm_fd(x11->renderer);
-	if (fd < 0) {
-		wlr_log(WLR_ERROR, "Failed to get DRM device FD from renderer");
-		return false;
-	}
-
-	drm_fd = fcntl(drm_fd, F_DUPFD_CLOEXEC, 0);
-	if (drm_fd < 0) {
-		wlr_log_errno(WLR_ERROR, "fcntl(F_DUPFD_CLOEXEC) failed");
-		return false;
-	}
-
-	struct wlr_gbm_allocator *alloc = wlr_gbm_allocator_create(drm_fd);
-	if (alloc == NULL) {
-		wlr_log(WLR_ERROR, "Failed to create GBM allocator");
-		return false;
-	}
-	x11->allocator = &alloc->base;
-
 	const struct wlr_drm_format_set *render_formats =
 		wlr_renderer_get_dmabuf_render_formats(x11->renderer);
 	if (render_formats == NULL) {