[PATCH 3/5] NET: IPV4: ARP: allow to invalidate specific ARP entries

[Maxim Levitsky <maximlevitsky@gmail.com>]

IPv4 over firewire needs to be able to remove ARP entries
from the ARP cache that belong to nodes that are removed, because
IPv4 over firewire uses ARP packets for private information
about nodes.

This information becomes invalid as soon as node drops
off the bus and when it reconnects, its only possible
to start takling to is after it responded to an ARP packet.
But ARP cache prevents such packets from being sent.

CC: netdev@vger.kernel.org
CC: "David S. Miller" <davem@davemloft.net>
CC: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
CC: James Morris <jmorris@namei.org>
CC: Patrick McHardy <kaber@trash.net>


Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
---
 include/net/arp.h |    1 +
 net/ipv4/arp.c    |   29 ++++++++++++++++++-----------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/include/net/arp.h b/include/net/arp.h
index f4cf6ce..91f0568 100644
--- a/include/net/arp.h
+++ b/include/net/arp.h
@@ -25,5 +25,6 @@ extern struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
 				  const unsigned char *src_hw,
 				  const unsigned char *target_hw);
 extern void arp_xmit(struct sk_buff *skb);
+int arp_invalidate(struct net_device *dev, __be32 ip);
 
 #endif	/* _ARP_H */
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index d8e540c..35b1272 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1142,6 +1142,23 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev)
 	return err;
 }
 
+int arp_invalidate(struct net_device *dev, __be32 ip)
+{
+	int err = -ENXIO;
+	struct neighbour *neigh = neigh_lookup(&arp_tbl, &ip, dev);
+
+	if (neigh) {
+		if (neigh->nud_state & ~NUD_NOARP)
+			err = neigh_update(neigh, NULL, NUD_FAILED,
+					   NEIGH_UPDATE_F_OVERRIDE|
+					   NEIGH_UPDATE_F_ADMIN);
+		neigh_release(neigh);
+	}
+
+	return err;
+}
+EXPORT_SYMBOL(arp_invalidate);
+
 static int arp_req_delete_public(struct net *net, struct arpreq *r,
 		struct net_device *dev)
 {
@@ -1162,7 +1179,6 @@ static int arp_req_delete(struct net *net, struct arpreq *r,
 {
 	int err;
 	__be32 ip;
-	struct neighbour *neigh;
 
 	if (r->arp_flags & ATF_PUBL)
 		return arp_req_delete_public(net, r, dev);
@@ -1180,16 +1196,7 @@ static int arp_req_delete(struct net *net, struct arpreq *r,
 		if (!dev)
 			return -EINVAL;
 	}
-	err = -ENXIO;
-	neigh = neigh_lookup(&arp_tbl, &ip, dev);
-	if (neigh) {
-		if (neigh->nud_state & ~NUD_NOARP)
-			err = neigh_update(neigh, NULL, NUD_FAILED,
-					   NEIGH_UPDATE_F_OVERRIDE|
-					   NEIGH_UPDATE_F_ADMIN);
-		neigh_release(neigh);
-	}
-	return err;
+	return arp_invalidate(dev, ip);
 }
 
 /*
-- 
1.7.1