backend-drm: prepare virtual output API for heterogeneous outputs

Stop plugins from overwriting the struct weston_output::destroy vfunc,
as that will be used by backends to recognize their outputs.
Instead, pass a plugin-specific destroy callback when creating the
virtual output.

See: https://gitlab.freedesktop.org/wayland/weston/-/issues/268

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

include/libweston/backend-drm.h

@@ -90,7 +90,7 @@ weston_drm_output_get_api(struct weston_compositor *compositor)
 	return (const struct weston_drm_output_api *)api;
 }
 
-#define WESTON_DRM_VIRTUAL_OUTPUT_API_NAME "weston_drm_virtual_output_api_v1"
+#define WESTON_DRM_VIRTUAL_OUTPUT_API_NAME "weston_drm_virtual_output_api_v2"
 
 struct drm_fb;
 typedef int (*submit_frame_cb)(struct weston_output *output, int fd,
@@ -101,12 +101,16 @@ struct weston_drm_virtual_output_api {
 	 * This is a low-level function, where the caller is expected to wrap
 	 * the weston_output function pointers as necessary to make the virtual
 	 * output useful. The caller must set up output make, model, serial,
-	 * physical size, the mode list and current mode.
+	 * physical size, the mode list and current mode. The destroy function
+	 * pointer must not be overwritten, as it is used by the DRM backend to
+	 * recognize its outputs. Instead, an auxiliary destroy callback has to
+	 * be provided as a parameter.
 	 *
 	 * Returns output on success, NULL on failure.
 	 */
 	struct weston_output* (*create_output)(struct weston_compositor *c,
-					       char *name);
+					       char *name,
+					       void (*destroy_func)(struct weston_output *base));
 
 	/** Set pixel format same as drm_output set_gbm_format().
 	 *

libweston/backend-drm/drm-internal.h

@@ -579,6 +579,7 @@ struct drm_output {
 	struct wl_event_source *pageflip_timer;
 
 	bool virtual;
+	void (*virtual_destroy)(struct weston_output *base);
 
 	submit_frame_cb virtual_submit_frame;
 };

libweston/backend-drm/drm-virtual.c

@@ -259,6 +259,9 @@ drm_virtual_output_destroy(struct weston_output *base)
 
 	drm_output_state_free(output->state_cur);
 
+	if (output->virtual_destroy)
+		output->virtual_destroy(base);
+
 	free(output);
 }
 
@@ -324,7 +327,8 @@ drm_virtual_output_disable(struct weston_output *base)
 }
 
 static struct weston_output *
-drm_virtual_output_create(struct weston_compositor *c, char *name)
+drm_virtual_output_create(struct weston_compositor *c, char *name,
+			  void (*destroy_func)(struct weston_output *))
 {
 	struct drm_output *output;
 	struct drm_backend *b = to_drm_backend(c);
@@ -343,6 +347,7 @@ drm_virtual_output_create(struct weston_compositor *c, char *name)
 	}
 
 	output->virtual = true;
+	output->virtual_destroy = destroy_func;
 	output->gbm_bo_flags = GBM_BO_USE_LINEAR | GBM_BO_USE_RENDERING;
 
 	weston_output_init(&output->base, c, name);

pipewire/pipewire-plugin.c

@@ -67,7 +67,6 @@ struct weston_pipewire {
 
 struct pipewire_output {
 	struct weston_output *output;
-	void (*saved_destroy)(struct weston_output *output);
 	int (*saved_enable)(struct weston_output *output);
 	int (*saved_disable)(struct weston_output *output);
 	int (*saved_start_repaint_loop)(struct weston_output *output);
@@ -316,8 +315,6 @@ pipewire_output_destroy(struct weston_output *base_output)
 		free(mode);
 	}
 
-	output->saved_destroy(base_output);
-
 	pw_stream_destroy(output->stream);
 
 	wl_list_remove(&output->link);
@@ -536,14 +533,12 @@ pipewire_output_create(struct weston_compositor *c, char *name)
 	pw_stream_add_listener(output->stream, &output->stream_listener,
 			       &stream_events, output);
 
-	output->output = api->create_output(c, name);
+	output->output = api->create_output(c, name, pipewire_output_destroy);
 	if (!output->output) {
 		weston_log("Cannot create virtual output\n");
 		goto err;
 	}
 
-	output->saved_destroy = output->output->destroy;
-	output->output->destroy = pipewire_output_destroy;
 	output->saved_enable = output->output->enable;
 	output->output->enable = pipewire_output_enable;
 	output->saved_disable = output->output->disable;

remoting/remoting-plugin.c

@@ -95,7 +95,6 @@ static const struct remoted_output_support_gbm_format supported_formats[] = {
 
 struct remoted_output {
 	struct weston_output *output;
-	void (*saved_destroy)(struct weston_output *output);
 	int (*saved_enable)(struct weston_output *output);
 	int (*saved_disable)(struct weston_output *output);
 	int (*saved_start_repaint_loop)(struct weston_output *output);
@@ -642,8 +641,6 @@ remoting_output_destroy(struct weston_output *output)
 		free(mode);
 	}
 
-	remoted_output->saved_destroy(output);
-
 	remoting_gst_pipeline_deinit(remoted_output);
 	remoting_gstpipe_release(&remoted_output->gstpipe);
 
@@ -763,14 +760,12 @@ remoting_output_create(struct weston_compositor *c, char *name)
 		goto err;
 	}
 
-	output->output = api->create_output(c, name);
+	output->output = api->create_output(c, name, remoting_output_destroy);
 	if (!output->output) {
 		weston_log("Can not create virtual output\n");
 		goto err;
 	}
 
-	output->saved_destroy = output->output->destroy;
-	output->output->destroy = remoting_output_destroy;
 	output->saved_enable = output->output->enable;
 	output->output->enable = remoting_output_enable;
 	output->saved_disable = output->output->disable;