ipv6: Export sernum update function

We are going to allow dead routes to stay in the FIB tree (e.g., when
they are part of a multipath route, directly connected route with no
carrier) and revive them when their nexthop device gains carrier or when
it is put administratively up.

This is equivalent to the addition of the route to the FIB tree and we
should therefore take care of updating the sernum of all the parent
nodes of the node where the route is stored. Otherwise, we risk sockets
caching and using sub-optimal dst entries.

Export the function that performs the above, so that it could be invoked
from fib6_ifup() later on.
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Acked-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -405,6 +405,7 @@ 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);
+void fib6_update_sernum_upto_root(struct net *net, struct rt6_info *rt);
 
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
 int fib6_rules_init(void);

net/ipv6/ip6_fib.c

@@ -1102,7 +1102,7 @@ void fib6_force_start_gc(struct net *net)
 			  jiffies + net->ipv6.sysctl.ip6_rt_gc_interval);
 }
 
-static void fib6_update_sernum_upto_root(struct rt6_info *rt,
+static void __fib6_update_sernum_upto_root(struct rt6_info *rt,
 					   int sernum)
 {
 	struct fib6_node *fn = rcu_dereference_protected(rt->rt6i_node,
@@ -1117,6 +1117,11 @@ static void fib6_update_sernum_upto_root(struct rt6_info *rt,
 	}
 }
 
+void fib6_update_sernum_upto_root(struct net *net, struct rt6_info *rt)
+{
+	__fib6_update_sernum_upto_root(rt, fib6_new_sernum(net));
+}
+
 /*
  *	Add routing information to the routing tree.
  *	<destination addr>/<source addr>
@@ -1230,7 +1235,7 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
 
 	err = fib6_add_rt2node(fn, rt, info, mxc, extack);
 	if (!err) {
-		fib6_update_sernum_upto_root(rt, sernum);
+		__fib6_update_sernum_upto_root(rt, sernum);
 		fib6_start_gc(info->nl_net, rt);
 	}