Re: [PATCH v4 1/2] Implement IP_UNICAST_IF socket option.

The IP_UNICAST_IF feature is needed by the Wine project.  This patch implements the feature by setting the outgoing interface in a similar fashion to that of IP_MULTICAST_IF.  A separate option is needed to handle this feature since the existing options do not provide all of the characteristics required by IP_UNICAST_IF, a summary is provided below.

--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c

@@ -375,6 +375,7 @@ lookup_protocol:
 	sk->sk_protocol	   = protocol;
 	sk->sk_backlog_rcv = sk->sk_prot->backlog_rcv;
 
+	inet->uc_index  = 0;
 	inet->uc_ttl	= -1;
 	inet->mc_loop	= 1;
 	inet->mc_ttl	= 1;

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c

@@ -917,6 +917,9 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		if (!saddr)
 			saddr = inet->mc_addr;
 		connected = 0;
+	} else if (!ipc.oif) {
+		ipc.oif = inet->uc_index;
+		connected = 0;
 	}