[NET]: Add dst->ifdown callback.

Use it to release protocol specific objects that may be
tied to a dst cache object, at ifdown time.  Currently
this is used to release ipv4/ipv6 specific device state.

include/net/dst.h

@@ -89,6 +89,7 @@ struct dst_ops
 	int			(*gc)(void);
 	struct dst_entry *	(*check)(struct dst_entry *, __u32 cookie);
 	void			(*destroy)(struct dst_entry *);
+	void			(*ifdown)(struct dst_entry *, int how);
 	struct dst_entry *	(*negative_advice)(struct dst_entry *);
 	void			(*link_failure)(struct sk_buff *);
 	void			(*update_pmtu)(struct dst_entry *dst, u32 mtu);

net/core/dst.c

@@ -230,8 +230,8 @@ static int dst_dev_event(struct notifier_block *this, unsigned long event, void
 				if (event!=NETDEV_DOWN &&
 				    dst->output == dst_discard_out) {
 					dst->dev = &loopback_dev;
-					dev_put(dev);
 					dev_hold(&loopback_dev);
+					dev_put(dev);
 					dst->output = dst_discard_out;
 					if (dst->neighbour && dst->neighbour->dev == dev) {
 						dst->neighbour->dev = &loopback_dev;
@@ -242,6 +242,8 @@ static int dst_dev_event(struct notifier_block *this, unsigned long event, void
 					dst->input = dst_discard_in;
 					dst->output = dst_discard_out;
 				}
+				if (dst->ops->ifdown)
+					dst->ops->ifdown(dst, event != NETDEV_DOWN);
 			}
 		}
 		spin_unlock_bh(&dst_lock);

net/ipv4/route.c

@@ -138,6 +138,7 @@ static struct timer_list rt_secret_timer;
 
 static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie);
 static void		 ipv4_dst_destroy(struct dst_entry *dst);
+static void		 ipv4_dst_ifdown(struct dst_entry *dst, int how);
 static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
 static void		 ipv4_link_failure(struct sk_buff *skb);
 static void		 ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu);
@@ -150,6 +151,7 @@ static struct dst_ops ipv4_dst_ops = {
 	.gc =			rt_garbage_collect,
 	.check =		ipv4_dst_check,
 	.destroy =		ipv4_dst_destroy,
+	.ifdown =		ipv4_dst_ifdown,
 	.negative_advice =	ipv4_negative_advice,
 	.link_failure =		ipv4_link_failure,
 	.update_pmtu =		ip_rt_update_pmtu,
@@ -1336,6 +1338,16 @@ static void ipv4_dst_destroy(struct dst_entry *dst)
 	}
 }
 
+static void ipv4_dst_ifdown(struct dst_entry *dst, int how)
+{
+	struct rtable *rt = (struct rtable *) dst;
+	struct in_device *idev = rt->idev;
+	if (idev) {
+		rt->idev = NULL;
+		in_dev_put(idev);
+	}
+}
+
 static void ipv4_link_failure(struct sk_buff *skb)
 {
 	struct rtable *rt;

net/ipv6/route.c

@@ -84,6 +84,7 @@ static struct rt6_info * ip6_rt_copy(struct rt6_info *ort);
 static struct dst_entry	*ip6_dst_check(struct dst_entry *dst, u32 cookie);
 static struct dst_entry *ip6_negative_advice(struct dst_entry *);
 static void		ip6_dst_destroy(struct dst_entry *);
+static void		ip6_dst_ifdown(struct dst_entry *, int how);
 static int		 ip6_dst_gc(void);
 
 static int		ip6_pkt_discard(struct sk_buff *skb);
@@ -98,6 +99,7 @@ static struct dst_ops ip6_dst_ops = {
 	.gc_thresh		=	1024,
 	.check			=	ip6_dst_check,
 	.destroy		=	ip6_dst_destroy,
+	.ifdown			=	ip6_dst_ifdown,
 	.negative_advice	=	ip6_negative_advice,
 	.link_failure		=	ip6_link_failure,
 	.update_pmtu		=	ip6_rt_update_pmtu,
@@ -143,9 +145,17 @@ static __inline__ struct rt6_info *ip6_dst_alloc(void)
 static void ip6_dst_destroy(struct dst_entry *dst)
 {
 	struct rt6_info *rt = (struct rt6_info *)dst;
-	if (rt->rt6i_idev != NULL)
-		in6_dev_put(rt->rt6i_idev);
+	struct inet6_dev *idev = rt->rt6i_idev;
 
+	if (idev != NULL) {
+		rt->rt6i_idev = NULL;
+		in6_dev_put(idev);
+	}	
+}
+
+static void ip6_dst_ifdown(struct dst_entry *dst, int how)
+{
+	ip6_dst_destroy(dst);
 }
 
 /*