expandable RAID-Z

*** 123,130 ****
--- 123,131 ----
          NULL,
          vdev_default_asize,
          NULL,                   /* io_start - not applicable to the root */
          NULL,                   /* io_done - not applicable to the root */
          vdev_root_state_change,
+         NULL,
          VDEV_TYPE_ROOT,         /* name of this vdev type */
          B_FALSE                 /* not a leaf vdev */
  };