ipv6: introduce a new function fib6_update_sernum()

This function takes a route as input and tries to update the sernum in
the fib6_node this route is associated with. It will be used in later
commit when adding a cached route into the exception table under that
route.
Signed-off-by: NWei Wang <weiwan@google.com>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -358,6 +358,8 @@ void __net_exit fib6_notifier_exit(struct net *net);
 unsigned int fib6_tables_seq_read(struct net *net);
 int fib6_tables_dump(struct net *net, struct notifier_block *nb);
 
+void fib6_update_sernum(struct rt6_info *rt);
+
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
 int fib6_rules_init(void);
 void fib6_rules_cleanup(void);

net/ipv6/ip6_fib.c

@@ -110,6 +110,20 @@ enum {
 	FIB6_NO_SERNUM_CHANGE = 0,
 };
 
+void fib6_update_sernum(struct rt6_info *rt)
+{
+	struct fib6_table *table = rt->rt6i_table;
+	struct net *net = dev_net(rt->dst.dev);
+	struct fib6_node *fn;
+
+	write_lock_bh(&table->tb6_lock);
+	fn = rcu_dereference_protected(rt->rt6i_node,
+			lockdep_is_held(&table->tb6_lock));
+	if (fn)
+		fn->fn_sernum = fib6_new_sernum(net);
+	write_unlock_bh(&table->tb6_lock);
+}
+
 /*
  *	Auxiliary address test functions for the radix tree.
  *