weston_buffer: Add mode to weston_buffer_reference

Add a mode argument to weston_buffer_reference which indicates whether a
buffer's storage may/will be accessed, or whether the underlying storage
will no longer be accessed, e.g. because it has been copied. This will
be used to retain a pointer to the weston_buffer whilst being able to
send a release event to the client.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/backend-drm/state-helpers.c

@@ -93,7 +93,8 @@ drm_plane_state_free(struct drm_plane_state *state, bool force)
 
 	if (force || state != state->plane->state_cur) {
 		drm_fb_unref(state->fb);
-		weston_buffer_reference(&state->fb_ref.buffer, NULL);
+		weston_buffer_reference(&state->fb_ref.buffer, NULL,
+					BUFFER_WILL_NOT_BE_ACCESSED);
 		weston_buffer_release_reference(&state->fb_ref.release, NULL);
 		free(state);
 	}
@@ -135,10 +136,20 @@ drm_plane_state_duplicate(struct drm_output_state *state_output,
 	 * buffer, then we must also transfer the reference on the client
 	 * buffer. */
 	if (src->fb) {
+		struct weston_buffer *buffer;
+
 		dst->fb = drm_fb_ref(src->fb);
 		memset(&dst->fb_ref, 0, sizeof(dst->fb_ref));
-		weston_buffer_reference(&dst->fb_ref.buffer,
-					src->fb_ref.buffer.buffer);
+
+		if (src->fb->type == BUFFER_CLIENT ||
+		    src->fb->type == BUFFER_DMABUF) {
+			buffer = src->fb_ref.buffer.buffer;
+		} else {
+			buffer = NULL;
+		}
+		weston_buffer_reference(&dst->fb_ref.buffer, buffer,
+					buffer ? BUFFER_MAY_BE_ACCESSED :
+					         BUFFER_WILL_NOT_BE_ACCESSED);
 		weston_buffer_release_reference(&dst->fb_ref.release,
 						src->fb_ref.release.buffer_release);
 	} else {

libweston/backend-drm/state-propose.c

@@ -139,7 +139,8 @@ drm_output_try_view_on_plane(struct drm_plane *plane,
 	assert(state->fb_ref.buffer.buffer == NULL);
 	assert(state->fb_ref.release.buffer_release == NULL);
 	weston_buffer_reference(&state->fb_ref.buffer,
-				surface->buffer_ref.buffer);
+				surface->buffer_ref.buffer,
+				BUFFER_MAY_BE_ACCESSED);
 	weston_buffer_release_reference(&state->fb_ref.release,
 					surface->buffer_release_ref.buffer_release);