nexthop: Emit a notification when a nexthop is added

[ Upstream commit 732d167 ]

Emit a notification in the nexthop notification chain when a new nexthop
is added (not replaced). The nexthop can either be a new group or a
single nexthop.

The notification is sent after the nexthop is inserted into the
red-black tree, as listeners might need to callback into the nexthop
code with the nexthop ID in order to mark the nexthop as offloaded.

A 'REPLACE' notification is emitted instead of 'ADD' as the distinction
between the two is not important for in-kernel listeners. In case the
listener is not familiar with the encoded nexthop ID, it can simply
treat it as a new one. This is also consistent with the route offload
API.

Changes since RFC:
* Reword commit message

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 390b3a3 ("nexthop: Forbid FDB status change while nexthop is in a group")
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: idosch

include/net/nexthop.h

@@ -105,7 +105,8 @@ struct nexthop {
 };
 
 enum nexthop_event_type {
-	NEXTHOP_EVENT_DEL
+	NEXTHOP_EVENT_DEL,
+	NEXTHOP_EVENT_REPLACE,
 };
 
 int register_nexthop_notifier(struct net *net, struct notifier_block *nb);

net/ipv4/nexthop.c

@@ -1191,7 +1191,11 @@ static int insert_nexthop(struct net *net, struct nexthop *new_nh,
 
 	rb_link_node_rcu(&new_nh->rb_node, parent, pp);
 	rb_insert_color(&new_nh->rb_node, root);
-	rc = 0;
+
+	rc = call_nexthop_notifiers(net, NEXTHOP_EVENT_REPLACE, new_nh, extack);
+	if (rc)
+		rb_erase(&new_nh->rb_node, &net->nexthop.rb_root);
+
 out:
 	if (!rc) {
 		nh_base_seq_inc(net);