VTSCSI_MAXSEG
struct iovec vsr_iov[VTSCSI_MAXSEG + SPLIT_IOV_ADDL_IOV];
.seg_max = VTSCSI_MAXSEG - 2,
n = vq_getchain(vq, req->vsr_iov, VTSCSI_MAXSEG, &vireq);
assert(n >= 1 && n <= VTSCSI_MAXSEG);
struct iovec iov[VTSCSI_MAXSEG];
n = vq_getchain(vq, iov, VTSCSI_MAXSEG, &req);
assert(n >= 1 && n <= VTSCSI_MAXSEG);