rpcrdma_segment_maxsz
rpcrdma_readseg_maxsz = 1 + rpcrdma_segment_maxsz,
size += rpcrdma_segment_maxsz * sizeof(__be32);
size += maxsegs * rpcrdma_segment_maxsz * sizeof(__be32);
segcount * rpcrdma_segment_maxsz * sizeof(*p));
const size_t len = rpcrdma_segment_maxsz * sizeof(__be32);