HAMMER_HEAD_TYPE_UNDO
case HAMMER_HEAD_TYPE_UNDO:
case HAMMER_HEAD_TYPE_UNDO:
if (undo->head.hdr_type != HAMMER_HEAD_TYPE_UNDO)
undo->head.hdr_type = HAMMER_HEAD_TYPE_UNDO;
tail->tail_type = HAMMER_HEAD_TYPE_UNDO;