backend/drm: Implement support for renderer loss recovery

This implementation is nearly identical to Sway's, except that
it also reloads the configuration, to spur on reloading the
server-side decorations.

v2: Fix style.
v3: Add a reset to the magnifier.
v4: Oops, restructure reset handler a bit.
v5: Commit the magnifier reset immediately, before freeing the
    lost allocator and renderer.
v6: Also check for failed render pass, which may return NULL.
v7: Add a second NULL test, just in case.

include/labwc.h

@@ -318,6 +318,8 @@ struct server {
 	 */
 	int pending_output_layout_change;
 
+	struct wl_listener renderer_lost;
+
 	struct wlr_gamma_control_manager_v1 *gamma_control_manager_v1;
 	struct wl_listener gamma_control_set_gamma;
 

include/magnifier.h

@@ -20,5 +20,6 @@ bool output_wants_magnification(struct output *output);
 void magnify(struct output *output, struct wlr_buffer *output_buffer,
 	struct wlr_box *damage);
 bool is_magnify_on(void);
+void magnify_reset(void);
 
 #endif /* LABWC_MAGNIFIER_H */

src/magnifier.c

@@ -10,6 +10,10 @@
 static bool magnify_on;
 static double mag_scale = 0.0;
 
+/* Reuse a single scratch buffer */
+static struct wlr_buffer *tmp_buffer = NULL;
+static struct wlr_texture *tmp_texture = NULL;
+
 #define CLAMP(in, lower, upper) MAX(MIN((in), (upper)), (lower))
 
 void
@@ -21,10 +25,6 @@ magnify(struct output *output, struct wlr_buffer *output_buffer, struct wlr_box
 	struct wlr_fbox src_box;
 	bool fullscreen = false;
 
-	/* Reuse a single scratch buffer */
-	static struct wlr_buffer *tmp_buffer = NULL;
-	static struct wlr_texture *tmp_texture = NULL;
-
 	/* TODO: This looks way too complicated to just get the used format */
 	struct wlr_drm_format wlr_drm_format = {0};
 	struct wlr_shm_attributes shm_attribs = {0};
@@ -125,6 +125,10 @@ magnify(struct output *output, struct wlr_buffer *output_buffer, struct wlr_box
 	/* Extract source region into temporary buffer */
 	struct wlr_render_pass *tmp_render_pass = wlr_renderer_begin_buffer_pass(
 		server->renderer, tmp_buffer, NULL);
+	if (!tmp_render_pass) {
+		wlr_log(WLR_ERROR, "Failed to begin magnifier render pass");
+		return;
+	}
 
 	wlr_buffer_lock(output_buffer);
 	struct wlr_texture *output_texture = wlr_texture_from_buffer(
@@ -152,6 +156,10 @@ magnify(struct output *output, struct wlr_buffer *output_buffer, struct wlr_box
 	/* Render to the output buffer itself */
 	tmp_render_pass = wlr_renderer_begin_buffer_pass(
 		server->renderer, output_buffer, NULL);
+	if (!tmp_render_pass) {
+		wlr_log(WLR_ERROR, "Failed to begin second magnifier render pass");
+		goto cleanup;
+	}
 
 	/* Borders */
 	if (fullscreen) {
@@ -286,6 +294,18 @@ magnify_set_scale(struct server *server, enum magnify_dir dir)
 	}
 }
 
+/* Reset any buffers held by the magnifier */
+void
+magnify_reset(void)
+{
+	if (tmp_texture && tmp_buffer) {
+		wlr_texture_destroy(tmp_texture);
+		wlr_buffer_drop(tmp_buffer);
+		tmp_buffer = NULL;
+		tmp_texture = NULL;
+	}
+}
+
 /* Report whether magnification is enabled */
 bool
 is_magnify_on(void)

src/server.c

@@ -28,6 +28,7 @@
 #include "idle.h"
 #include "labwc.h"
 #include "layers.h"
+#include "magnifier.h"
 #include "menu/menu.h"
 #include "output-state.h"
 #include "output-virtual.h"
@@ -249,6 +250,51 @@ get_headless_backend(struct wlr_backend *backend, void *data)
 	}
 }
 
+static void
+handle_renderer_lost(struct wl_listener *listener, void *data)
+{
+	struct server *server = wl_container_of(listener, server, renderer_lost);
+
+	wlr_log(WLR_INFO, "Re-creating renderer after GPU reset");
+
+	struct wlr_renderer *renderer = wlr_renderer_autocreate(server->backend);
+	if (!renderer) {
+		wlr_log(WLR_ERROR, "Unable to create renderer");
+		return;
+	}
+
+	struct wlr_allocator *allocator =
+		wlr_allocator_autocreate(server->backend, renderer);
+	if (!allocator) {
+		wlr_log(WLR_ERROR, "Unable to create allocator");
+		wlr_renderer_destroy(renderer);
+		return;
+	}
+
+	struct wlr_renderer *old_renderer = server->renderer;
+	struct wlr_allocator *old_allocator = server->allocator;
+	server->renderer = renderer;
+	server->allocator = allocator;
+
+	wl_list_remove(&server->renderer_lost.link);
+	wl_signal_add(&server->renderer->events.lost, &server->renderer_lost);
+
+	wlr_compositor_set_renderer(compositor, renderer);
+
+	struct output *output;
+	wl_list_for_each(output, &server->outputs, link) {
+		wlr_output_init_render(output->wlr_output,
+			server->allocator, server->renderer);
+	}
+
+	reload_config_and_theme(server);
+
+	magnify_reset();
+
+	wlr_allocator_destroy(old_allocator);
+	wlr_renderer_destroy(old_renderer);
+}
+
 void
 server_init(struct server *server)
 {
@@ -336,6 +382,9 @@ server_init(struct server *server)
 		exit(EXIT_FAILURE);
 	}
 
+	server->renderer_lost.notify = handle_renderer_lost;
+	wl_signal_add(&server->renderer->events.lost, &server->renderer_lost);
+
 	wlr_renderer_init_wl_display(server->renderer, server->wl_display);
 
 	/*