render/drm_syncobj: add wlr_drm_syncobj_timeline_transfer()

include/wlr/render/drm_syncobj.h

@@ -62,6 +62,13 @@ struct wlr_drm_syncobj_timeline *wlr_drm_syncobj_timeline_ref(struct wlr_drm_syn
  * Unreference a synchronization timeline.
  */
 void wlr_drm_syncobj_timeline_unref(struct wlr_drm_syncobj_timeline *timeline);
+/**
+ * Transfer a point from a timeline to another.
+ *
+ * Both timelines must have been created with the same DRM FD.
+ */
+bool wlr_drm_syncobj_timeline_transfer(struct wlr_drm_syncobj_timeline *dst,
+	uint64_t dst_point, struct wlr_drm_syncobj_timeline *src, uint64_t src_point);
 /**
  * Check if a timeline point has been signalled or has materialized.
  *

render/drm_syncobj.c

@@ -67,6 +67,19 @@ void wlr_drm_syncobj_timeline_unref(struct wlr_drm_syncobj_timeline *timeline) {
 	free(timeline);
 }
 
+bool wlr_drm_syncobj_timeline_transfer(struct wlr_drm_syncobj_timeline *dst,
+		uint64_t dst_point, struct wlr_drm_syncobj_timeline *src, uint64_t src_point) {
+	assert(dst->drm_fd == src->drm_fd);
+
+	if (drmSyncobjTransfer(dst->drm_fd, dst->handle, dst_point,
+			src->handle, src_point, 0) != 0) {
+		wlr_log_errno(WLR_ERROR, "drmSyncobjTransfer failed");
+		return false;
+	}
+
+	return true;
+}
+
 int wlr_drm_syncobj_timeline_export_sync_file(struct wlr_drm_syncobj_timeline *timeline,
 		uint64_t src_point) {
 	int sync_file_fd = -1;