nvme_request_allocate_null
req = nvme_request_allocate_null(&ctrlr->adminq, cb_fn, cb_arg);
req = nvme_request_allocate_null(&ctrlr->adminq,
extern struct nvme_request *nvme_request_allocate_null(struct nvme_qpair *qpair,
req = nvme_request_allocate_null(qpair, cb_fn, cb_arg);
req = nvme_request_allocate_null(qpair, cb_fn, cb_arg);