+
+ /**
+ * Declare intention to instaintiate extended layout component.
+ *
+ * \param[in] env execution environment
+ * \param[in] dt DT object
+ * \param[in] layout data structure to describe the changes to
+ * the DT object's layout
+ * \param[in] buf buffer containing client's lovea or empty
+ *
+ * \retval 0 success
+ * \retval -ne error code
+ */
+ int (*do_declare_layout_change)(const struct lu_env *env,
+ struct dt_object *dt,
+ struct md_layout_change *mlc,
+ struct thandle *th);
+
+ /**
+ * Client is trying to write to un-instantiated layout component.
+ *
+ * \param[in] env execution environment
+ * \param[in] dt DT object
+ * \param[in] layout data structure to describe the changes to
+ * the DT object's layout
+ * \param[in] buf buffer containing client's lovea or empty
+ *
+ * \retval 0 success
+ * \retval -ne error code
+ */
+ int (*do_layout_change)(const struct lu_env *env, struct dt_object *dt,
+ struct md_layout_change *mlc,
+ struct thandle *th);
+};
+
+enum dt_bufs_type {
+ DT_BUFS_TYPE_READ = 0x0000,
+ DT_BUFS_TYPE_WRITE = 0x0001,
+ DT_BUFS_TYPE_READAHEAD = 0x0002,
+ DT_BUFS_TYPE_LOCAL = 0x0004,