svcrdma: Use parsed chunk lists to detect reverse direction replies

Refactor: Don't duplicate header decoding smarts here. Instead, use
the new parsed chunk lists.

Note that the XID sanity test is also removed. The XID is already
looked up by the cb handler, and is rejected if it's not recognized.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc_rdma.h

@@ -144,6 +144,7 @@ struct svc_rdma_recv_ctxt {
 	unsigned int		rc_page_count;
 	unsigned int		rc_hdr_count;
 	u32			rc_inv_rkey;
+	__be32			rc_msgtype;
 
 	struct svc_rdma_pcl	rc_call_pcl;
 

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

@@ -668,7 +668,8 @@ static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg,
 	if (*p != rpcrdma_version)
 		goto out_version;
 	p += 2;
-	switch (*p) {
+	rctxt->rc_msgtype = *p;
+	switch (rctxt->rc_msgtype) {
 	case rdma_msg:
 		break;
 	case rdma_nomsg:
@@ -762,30 +763,28 @@ static void svc_rdma_send_error(struct svcxprt_rdma *rdma,
  * the RPC/RDMA header small and fixed in size, so it is
  * straightforward to check the RPC header's direction field.
  */
-static bool svc_rdma_is_backchannel_reply(struct svc_xprt *xprt,
-					  __be32 *rdma_resp)
+static bool svc_rdma_is_reverse_direction_reply(struct svc_xprt *xprt,
+						struct svc_rdma_recv_ctxt *rctxt)
 {
-	__be32 *p;
+	__be32 *p = rctxt->rc_recv_buf;
 
 	if (!xprt->xpt_bc_xprt)
 		return false;
 
-	p = rdma_resp + 3;
-	if (*p++ != rdma_msg)
+	if (rctxt->rc_msgtype != rdma_msg)
 		return false;
 
-	if (*p++ != xdr_zero)
+	if (!pcl_is_empty(&rctxt->rc_call_pcl))
+		return false;
+	if (!pcl_is_empty(&rctxt->rc_read_pcl))
 		return false;
-	if (*p++ != xdr_zero)
+	if (!pcl_is_empty(&rctxt->rc_write_pcl))
 		return false;
-	if (*p++ != xdr_zero)
+	if (!pcl_is_empty(&rctxt->rc_reply_pcl))
 		return false;
 
-	/* XID sanity */
-	if (*p++ != *rdma_resp)
-		return false;
-	/* call direction */
-	if (*p == cpu_to_be32(RPC_CALL))
+	/* RPC call direction */
+	if (*(p + 8) == cpu_to_be32(RPC_CALL))
 		return false;
 
 	return true;
@@ -868,7 +867,7 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
 		goto out_drop;
 	rqstp->rq_xprt_hlen = ret;
 
-	if (svc_rdma_is_backchannel_reply(xprt, p))
+	if (svc_rdma_is_reverse_direction_reply(xprt, ctxt))
 		goto out_backchannel;
 
 	svc_rdma_get_inv_rkey(rdma_xprt, ctxt);