svcrdma: De-duplicate code that locates Write and Reply chunks

Cache the locations of the Requester-provided Write list and Reply
chunk so that the Send path doesn't need to parse the Call header
again.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc_rdma.h

@@ -138,6 +138,8 @@ struct svc_rdma_recv_ctxt {
 	unsigned int		rc_page_count;
 	unsigned int		rc_hdr_count;
 	u32			rc_inv_rkey;
+	__be32			*rc_write_list;
+	__be32			*rc_reply_chunk;
 	unsigned int		rc_read_payload_offset;
 	unsigned int		rc_read_payload_length;
 	struct page		*rc_pages[RPCSVC_MAXPAGES];

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

@@ -479,6 +479,7 @@ static bool xdr_check_write_list(struct svc_rdma_recv_ctxt *rctxt)
 	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
 	if (!p)
 		return false;
+	rctxt->rc_write_list = p;
 	while (*p != xdr_zero) {
 		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_WRITE_CHUNK))
 			return false;
@@ -487,6 +488,8 @@ static bool xdr_check_write_list(struct svc_rdma_recv_ctxt *rctxt)
 		if (!p)
 			return false;
 	}
+	if (!chcount)
+		rctxt->rc_write_list = NULL;
 	return chcount < 2;
 }
 
@@ -509,9 +512,13 @@ static bool xdr_check_reply_chunk(struct svc_rdma_recv_ctxt *rctxt)
 	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
 	if (!p)
 		return false;
-	if (*p != xdr_zero)
+	rctxt->rc_reply_chunk = p;
+	if (*p != xdr_zero) {
 		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_SPECIAL_CHUNK))
 			return false;
+	} else {
+		rctxt->rc_reply_chunk = NULL;
+	}
 	return true;
 }
 

net/sunrpc/xprtrdma/svc_rdma_sendto.c

@@ -449,36 +449,6 @@ static void svc_rdma_xdr_encode_reply_chunk(__be32 *rdma_resp, __be32 *rp_ch,
 	xdr_encode_write_chunk(p, rp_ch, consumed);
 }
 
-/* Parse the RPC Call's transport header.
- */
-static void svc_rdma_get_write_arrays(__be32 *rdma_argp,
-				      __be32 **write, __be32 **reply)
-{
-	__be32 *p;
-
-	p = rdma_argp + rpcrdma_fixed_maxsz;
-
-	/* Read list */
-	while (*p++ != xdr_zero)
-		p += 5;
-
-	/* Write list */
-	if (*p != xdr_zero) {
-		*write = p;
-		while (*p++ != xdr_zero)
-			p += 1 + be32_to_cpu(*p) * 4;
-	} else {
-		*write = NULL;
-		p++;
-	}
-
-	/* Reply chunk */
-	if (*p != xdr_zero)
-		*reply = p;
-	else
-		*reply = NULL;
-}
-
 static int svc_rdma_dma_map_page(struct svcxprt_rdma *rdma,
 				 struct svc_rdma_send_ctxt *ctxt,
 				 struct page *page,
@@ -813,14 +783,14 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
 	struct svcxprt_rdma *rdma =
 		container_of(xprt, struct svcxprt_rdma, sc_xprt);
 	struct svc_rdma_recv_ctxt *rctxt = rqstp->rq_xprt_ctxt;
-	__be32 *p, *rdma_argp, *rdma_resp, *wr_lst, *rp_ch;
+	__be32 *rdma_argp = rctxt->rc_recv_buf;
+	__be32 *wr_lst = rctxt->rc_write_list;
+	__be32 *rp_ch = rctxt->rc_reply_chunk;
 	struct xdr_buf *xdr = &rqstp->rq_res;
 	struct svc_rdma_send_ctxt *sctxt;
+	__be32 *p, *rdma_resp;
 	int ret;
 
-	rdma_argp = rctxt->rc_recv_buf;
-	svc_rdma_get_write_arrays(rdma_argp, &wr_lst, &rp_ch);
-
 	/* Create the RDMA response header. xprt->xpt_mutex,
 	 * acquired in svc_send(), serializes RPC replies. The
 	 * code path below that inserts the credit grant value