SUNRPC: Restructure svc_udp_recvfrom()

Clean up. At this point, we are not ready yet to support bio_vecs in
the UDP transport implementation. However, we can clean up
svc_udp_recvfrom() to match the tracing and straight-lining recently
changes made in svc_tcp_recvfrom().
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/trace/events/sunrpc.h

@@ -1501,6 +1501,8 @@ DECLARE_EVENT_CLASS(svcsock_class,
 			TP_ARGS(xprt, result))
 
 DEFINE_SVCSOCK_EVENT(udp_send);
+DEFINE_SVCSOCK_EVENT(udp_recv);
+DEFINE_SVCSOCK_EVENT(udp_recv_err);
 DEFINE_SVCSOCK_EVENT(tcp_send);
 DEFINE_SVCSOCK_EVENT(tcp_recv);
 DEFINE_SVCSOCK_EVENT(tcp_recv_eagain);

net/sunrpc/svcsock.c

@@ -425,8 +425,15 @@ static int svc_udp_get_dest_address(struct svc_rqst *rqstp,
 	return 0;
 }
 
-/*
- * Receive a datagram from a UDP socket.
+/**
+ * svc_udp_recvfrom - Receive a datagram from a UDP socket.
+ * @rqstp: request structure into which to receive an RPC Call
+ *
+ * Called in a loop when XPT_DATA has been set.
+ *
+ * Returns:
+ *   On success, the number of bytes in a received RPC Call, or
+ *   %0 if a complete RPC Call message was not ready to return
  */
 static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 {
@@ -460,20 +467,14 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 	    svc_sock_setbufsize(svsk, serv->sv_nrthreads + 3);
 
 	clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
-	skb = NULL;
 	err = kernel_recvmsg(svsk->sk_sock, &msg, NULL,
 			     0, 0, MSG_PEEK | MSG_DONTWAIT);
-	if (err >= 0)
-		skb = skb_recv_udp(svsk->sk_sk, 0, 1, &err);
-
-	if (skb == NULL) {
-		if (err != -EAGAIN) {
-			/* possibly an icmp error */
-			dprintk("svc: recvfrom returned error %d\n", -err);
-			set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
-		}
-		return 0;
-	}
+	if (err < 0)
+		goto out_recv_err;
+	skb = skb_recv_udp(svsk->sk_sk, 0, 1, &err);
+	if (!skb)
+		goto out_recv_err;
+
 	len = svc_addr_len(svc_addr(rqstp));
 	rqstp->rq_addrlen = len;
 	if (skb->tstamp == 0) {
@@ -484,26 +485,21 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 	sock_write_timestamp(svsk->sk_sk, skb->tstamp);
 	set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); /* there may be more data... */
 
-	len  = skb->len;
+	len = skb->len;
 	rqstp->rq_arg.len = len;
+	trace_svcsock_udp_recv(&svsk->sk_xprt, len);
 
 	rqstp->rq_prot = IPPROTO_UDP;
 
-	if (!svc_udp_get_dest_address(rqstp, cmh)) {
-		net_warn_ratelimited("svc: received unknown control message %d/%d; dropping RPC reply datagram\n",
-				     cmh->cmsg_level, cmh->cmsg_type);
-		goto out_free;
-	}
+	if (!svc_udp_get_dest_address(rqstp, cmh))
+		goto out_cmsg_err;
 	rqstp->rq_daddrlen = svc_addr_len(svc_daddr(rqstp));
 
 	if (skb_is_nonlinear(skb)) {
 		/* we have to copy */
 		local_bh_disable();
-		if (csum_partial_copy_to_xdr(&rqstp->rq_arg, skb)) {
-			local_bh_enable();
-			/* checksum error */
-			goto out_free;
-		}
+		if (csum_partial_copy_to_xdr(&rqstp->rq_arg, skb))
+			goto out_bh_enable;
 		local_bh_enable();
 		consume_skb(skb);
 	} else {
@@ -531,6 +527,20 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 		serv->sv_stats->netudpcnt++;
 
 	return len;
+
+out_recv_err:
+	if (err != -EAGAIN) {
+		/* possibly an icmp error */
+		set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
+	}
+	trace_svcsock_udp_recv_err(&svsk->sk_xprt, err);
+	return 0;
+out_cmsg_err:
+	net_warn_ratelimited("svc: received unknown control message %d/%d; dropping RPC reply datagram\n",
+			     cmh->cmsg_level, cmh->cmsg_type);
+	goto out_free;
+out_bh_enable:
+	local_bh_enable();
 out_free:
 	kfree_skb(skb);
 	return 0;