SUNRPC: Enable the keepalive option for TCP sockets

For NFSv4 we want to avoid retransmitting RPC calls unless the TCP
connection breaks. However we still want to detect TCP connection
breakage as soon as possible. Do this by setting the keepalive option
with the idle timeout and count set to the 'timeo' and 'retrans' mount
options.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xprtsock.c

@@ -2112,6 +2112,19 @@ static int xs_tcp_finish_connecting(struct rpc_xprt *xprt, struct socket *sock)
 
 	if (!transport->inet) {
 		struct sock *sk = sock->sk;
+		unsigned int keepidle = xprt->timeout->to_initval / HZ;
+		unsigned int keepcnt = xprt->timeout->to_retries + 1;
+		unsigned int opt_on = 1;
+
+		/* TCP Keepalive options */
+		kernel_setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE,
+				(char *)&opt_on, sizeof(opt_on));
+		kernel_setsockopt(sock, SOL_TCP, TCP_KEEPIDLE,
+				(char *)&keepidle, sizeof(keepidle));
+		kernel_setsockopt(sock, SOL_TCP, TCP_KEEPINTVL,
+				(char *)&keepidle, sizeof(keepidle));
+		kernel_setsockopt(sock, SOL_TCP, TCP_KEEPCNT,
+				(char *)&keepcnt, sizeof(keepcnt));
 
 		write_lock_bh(&sk->sk_callback_lock);