[PATCH] RPC: make sure to get the same local port number when reconnecting

 Implement a best practice: if the remote end drops our connection, try to
 reconnect using the same port number.  This is important because the NFS
 server's Duplicate Reply Cache often hashes on the source port number.
 If the client reuses the port number when it reconnects, the server's DRC
 will be more effective.

 Based on suggestions by Mike Eisler, Olaf Kirch, and Alexey Kuznetsky.

 Test-plan:
 Destructive testing.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xprtsock.c

@@ -362,6 +362,8 @@ static int xs_tcp_send_request(struct rpc_task *task)
  * xs_close - close a socket
  * @xprt: transport
  *
+ * This is used when all requests are complete; ie, no DRC state remains
+ * on the server we want to save.
  */
 static void xs_close(struct rpc_xprt *xprt)
 {
@@ -949,6 +951,30 @@ static void xs_udp_connect_worker(void *args)
 	xprt_clear_connecting(xprt);
 }
 
+/*
+ * We need to preserve the port number so the reply cache on the server can
+ * find our cached RPC replies when we get around to reconnecting.
+ */
+static void xs_tcp_reuse_connection(struct rpc_xprt *xprt)
+{
+	int result;
+	struct socket *sock = xprt->sock;
+	struct sockaddr any;
+
+	dprintk("RPC:      disconnecting xprt %p to reuse port\n", xprt);
+
+	/*
+	 * Disconnect the transport socket by doing a connect operation
+	 * with AF_UNSPEC.  This should return immediately...
+	 */
+	memset(&any, 0, sizeof(any));
+	any.sa_family = AF_UNSPEC;
+	result = sock->ops->connect(sock, &any, sizeof(any), 0);
+	if (result)
+		dprintk("RPC:      AF_UNSPEC connect return code %d\n",
+				result);
+}
+
 /**
  * xs_tcp_connect_worker - connect a TCP socket to a remote endpoint
  * @args: RPC transport to connect
@@ -966,9 +992,8 @@ static void xs_tcp_connect_worker(void *args)
 
 	dprintk("RPC:      xs_tcp_connect_worker for xprt %p\n", xprt);
 
-	/* Start by resetting any existing socket state */
-	xs_close(xprt);
-
+	if (!xprt->sock) {
+		/* start from scratch */
 		if ((err = sock_create_kern(PF_INET, SOCK_STREAM, IPPROTO_TCP, &sock)) < 0) {
 			dprintk("RPC:      can't create TCP transport socket (%d).\n", -err);
 			goto out;
@@ -978,6 +1003,9 @@ static void xs_tcp_connect_worker(void *args)
 			sock_release(sock);
 			goto out;
 		}
+	} else
+		/* "close" the socket, preserving the local port */
+		xs_tcp_reuse_connection(xprt);
 
 	if (!xprt->inet) {
 		struct sock *sk = sock->sk;
@@ -991,7 +1019,12 @@ static void xs_tcp_connect_worker(void *args)
 		sk->sk_data_ready = xs_tcp_data_ready;
 		sk->sk_state_change = xs_tcp_state_change;
 		sk->sk_write_space = xs_tcp_write_space;
-		tcp_sk(sk)->nonagle = 1;
+
+		/* socket options */
+		sk->sk_userlocks |= SOCK_BINDPORT_LOCK;
+		sock_reset_flag(sk, SOCK_LINGER);
+		tcp_sk(sk)->linger2 = 0;
+		tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF;
 
 		xprt_clear_connected(xprt);
 
@@ -1012,6 +1045,14 @@ static void xs_tcp_connect_worker(void *args)
 			case -EINPROGRESS:
 			case -EALREADY:
 				goto out_clear;
+			case -ECONNREFUSED:
+			case -ECONNRESET:
+				/* retry with existing socket, after a delay */
+				break;
+			default:
+				/* get rid of existing socket, and retry */
+				xs_close(xprt);
+				break;
 		}
 	}
 out: