vioblk_req_hdr
struct vioblk_req_hdr vbh;
sizeof (struct vioblk_req_hdr), VIRTIO_DIR_DEVICE_READS) !=
sizeof (struct vioblk_req_hdr), sizeof (uint8_t),
sizeof (struct vioblk_req_hdr)), &status, sizeof (status));
sizeof (struct vioblk_req_hdr) + sizeof (uint8_t),