From mboxrd@z Thu Jan  1 00:00:00 1970
From: Brian Haley <brian.haley@hp.com>
Subject: [IPv6] Update setsockopt(IPV6_MULTICAST_IF) to support RFC 3493,
 try2
Date: Thu, 11 Oct 2007 13:40:08 -0400
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Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	David Stevens <dlstevens@us.ibm.com>
To: David Miller <davem@davemloft.net>,
	YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
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Hi,

 From RFC 3493, Section 5.2:

       IPV6_MULTICAST_IF

          Set the interface to use for outgoing multicast packets.  The
          argument is the index of the interface to use.  If the
          interface index is specified as zero, the system selects the
          interface (for example, by looking up the address in a routing
          table and using the resulting interface).

This patch adds support for (index == 0) to reset the value to it's 
original state, allowing the system to choose the best interface.  IPv4 
already behaves this way.

-Brian


Signed-off-by: Brian Haley <brian.haley@hp.com>

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diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 532425d..1334fc1 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -539,12 +539,15 @@ done:
 	case IPV6_MULTICAST_IF:
 		if (sk->sk_type == SOCK_STREAM)
 			goto e_inval;
-		if (sk->sk_bound_dev_if && sk->sk_bound_dev_if != val)
-			goto e_inval;
 
-		if (__dev_get_by_index(&init_net, val) == NULL) {
-			retv = -ENODEV;
-			break;
+		if (val) {
+			if (sk->sk_bound_dev_if && sk->sk_bound_dev_if != val)
+				goto e_inval;
+
+			if (__dev_get_by_index(&init_net, val) == NULL) {
+				retv = -ENODEV;
+				break;
+			}
 		}
 		np->mcast_oif = val;
 		retv = 0;

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