[PATCH RFC 6/9] svcrdma: De-duplicate code that locates Write and Reply chunks

[Chuck Lever <chuck.lever@oracle.com>]

Cache the locations of the first Write chunk and the 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         |    2 ++
 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |   24 +++++++++++++-------
 net/sunrpc/xprtrdma/svc_rdma_sendto.c   |   38 +++----------------------------
 3 files changed, 22 insertions(+), 42 deletions(-)

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index 04e4a34d1c6a..07baeb5f93c1 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -137,6 +137,8 @@ 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];
diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index 2f16c0625226..91abe08f7d75 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -444,15 +444,17 @@ static __be32 *xdr_check_write_chunk(__be32 *p, const __be32 *end,
  * - This implementation supports only one Write chunk.
  *
  * Sanity checks:
- * - Write list does not overflow buffer.
+ * - Write list does not overflow Receive buffer.
  * - Segment size limited by largest NFS data payload.
  *
  * Returns pointer to the following Reply chunk.
  */
-static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
+static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end,
+				    struct svc_rdma_recv_ctxt *ctxt)
 {
 	u32 chcount;
 
+	ctxt->rc_write_list = p;
 	chcount = 0;
 	while (*p++ != xdr_zero) {
 		p = xdr_check_write_chunk(p, end, MAX_BYTES_WRITE_SEG);
@@ -461,6 +463,8 @@ static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
 		if (chcount++ > 1)
 			return NULL;
 	}
+	if (!chcount)
+		ctxt->rc_write_list = NULL;
 	return p;
 }
 
@@ -472,13 +476,16 @@ static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
  *
  * Returns pointer to the following RPC header.
  */
-static __be32 *xdr_check_reply_chunk(__be32 *p, const __be32 *end)
+static __be32 *xdr_check_reply_chunk(__be32 *p, const __be32 *end,
+				     struct svc_rdma_recv_ctxt *ctxt)
 {
+	ctxt->rc_reply_chunk = p;
 	if (*p++ != xdr_zero) {
 		p = xdr_check_write_chunk(p, end, MAX_BYTES_SPECIAL_SEG);
 		if (!p)
 			return NULL;
-	}
+	} else
+		ctxt->rc_reply_chunk = NULL;
 	return p;
 }
 
@@ -554,7 +561,8 @@ static void svc_rdma_get_inv_rkey(struct svcxprt_rdma *rdma,
  * Assumptions:
  * - The transport header is entirely contained in the head iovec.
  */
-static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg)
+static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg,
+				   struct svc_rdma_recv_ctxt *ctxt)
 {
 	__be32 *p, *end, *rdma_argp;
 	unsigned int hdr_len;
@@ -587,10 +595,10 @@ static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg)
 	p = xdr_check_read_list(rdma_argp + 4, end);
 	if (!p)
 		goto out_inval;
-	p = xdr_check_write_list(p, end);
+	p = xdr_check_write_list(p, end, ctxt);
 	if (!p)
 		goto out_inval;
-	p = xdr_check_reply_chunk(p, end);
+	p = xdr_check_reply_chunk(p, end, ctxt);
 	if (!p)
 		goto out_inval;
 	if (p > end)
@@ -792,7 +800,7 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
 	rqstp->rq_next_page = rqstp->rq_respages;
 
 	p = (__be32 *)rqstp->rq_arg.head[0].iov_base;
-	ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg);
+	ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg, ctxt);
 	if (ret < 0)
 		goto out_err;
 	if (ret == 0)
diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index 40b4843be869..3c0e41d378bc 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -454,36 +454,6 @@ 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,
@@ -842,14 +812,14 @@ 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