VIRTIO_CONFIG1_QUEUE_SELECT
bus_space_write_2(iot, ioh, VIRTIO_CONFIG1_QUEUE_SELECT, idx);
bus_space_write_2(iot, ioh, VIRTIO_CONFIG1_QUEUE_SELECT, vq->vq_index);
bus_space_write_2(iot, ioh, VIRTIO_CONFIG1_QUEUE_SELECT, qid);