xprtrdma: Clean up rpcrdma_bc_marshal_reply()

Same changes as in rpcrdma_marshal_req(). This removes
C-structure style encoding from the backchannel.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/backchannel.c

@@ -49,6 +49,7 @@ static int rpcrdma_bc_setup_rqst(struct rpcrdma_xprt *r_xprt,
 	if (IS_ERR(rb))
 		goto out_fail;
 	req->rl_rdmabuf = rb;
+	xdr_buf_init(&req->rl_hdrbuf, rb->rg_base, rdmab_length(rb));
 
 	size = r_xprt->rx_data.inline_rsize;
 	rb = rpcrdma_alloc_regbuf(size, DMA_TO_DEVICE, GFP_KERNEL);
@@ -202,20 +203,24 @@ size_t xprt_rdma_bc_maxpayload(struct rpc_xprt *xprt)
  */
 int rpcrdma_bc_marshal_reply(struct rpc_rqst *rqst)
 {
-	struct rpc_xprt *xprt = rqst->rq_xprt;
-	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
+	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(rqst->rq_xprt);
 	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
-	struct rpcrdma_msg *headerp;
+	__be32 *p;
 
-	headerp = rdmab_to_msg(req->rl_rdmabuf);
-	headerp->rm_xid = rqst->rq_xid;
-	headerp->rm_vers = rpcrdma_version;
-	headerp->rm_credit =
-			cpu_to_be32(r_xprt->rx_buf.rb_bc_srv_max_requests);
-	headerp->rm_type = rdma_msg;
-	headerp->rm_body.rm_chunks[0] = xdr_zero;
-	headerp->rm_body.rm_chunks[1] = xdr_zero;
-	headerp->rm_body.rm_chunks[2] = xdr_zero;
+	rpcrdma_set_xdrlen(&req->rl_hdrbuf, 0);
+	xdr_init_encode(&req->rl_stream, &req->rl_hdrbuf,
+			req->rl_rdmabuf->rg_base);
+
+	p = xdr_reserve_space(&req->rl_stream, 28);
+	if (unlikely(!p))
+		return -EIO;
+	*p++ = rqst->rq_xid;
+	*p++ = rpcrdma_version;
+	*p++ = cpu_to_be32(r_xprt->rx_buf.rb_bc_srv_max_requests);
+	*p++ = rdma_msg;
+	*p++ = xdr_zero;
+	*p++ = xdr_zero;
+	*p = xdr_zero;
 
 	if (!rpcrdma_prepare_send_sges(&r_xprt->rx_ia, req, RPCRDMA_HDRLEN_MIN,
 				       &rqst->rq_snd_buf, rpcrdma_noch))