net: introduce a helper to move notifier block to different namespace

Currently, net_dev() netdev notifier variant follows the netdev with
per-net notifier from namespace to namespace. This is implemented
by move_netdevice_notifiers_dev_net() helper.

For devlink it is needed to re-register per-net notifier during
devlink reload. Introduce a new helper called
move_netdevice_notifier_net() and share the unregister/register code
with existing move_netdevice_notifiers_dev_net() helper.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -2826,6 +2826,8 @@ int unregister_netdevice_notifier(struct notifier_block *nb);
 int register_netdevice_notifier_net(struct net *net, struct notifier_block *nb);
 int unregister_netdevice_notifier_net(struct net *net,
 				      struct notifier_block *nb);
+void move_netdevice_notifier_net(struct net *src_net, struct net *dst_net,
+				 struct notifier_block *nb);
 int register_netdevice_notifier_dev_net(struct net_device *dev,
 					struct notifier_block *nb,
 					struct netdev_net_notifier *nn);

net/core/dev.c

@@ -1861,6 +1861,22 @@ int unregister_netdevice_notifier_net(struct net *net,
 }
 EXPORT_SYMBOL(unregister_netdevice_notifier_net);
 
+static void __move_netdevice_notifier_net(struct net *src_net,
+					  struct net *dst_net,
+					  struct notifier_block *nb)
+{
+	__unregister_netdevice_notifier_net(src_net, nb);
+	__register_netdevice_notifier_net(dst_net, nb, true);
+}
+
+void move_netdevice_notifier_net(struct net *src_net, struct net *dst_net,
+				 struct notifier_block *nb)
+{
+	rtnl_lock();
+	__move_netdevice_notifier_net(src_net, dst_net, nb);
+	rtnl_unlock();
+}
+
 int register_netdevice_notifier_dev_net(struct net_device *dev,
 					struct notifier_block *nb,
 					struct netdev_net_notifier *nn)
@@ -1897,10 +1913,8 @@ static void move_netdevice_notifiers_dev_net(struct net_device *dev,
 {
 	struct netdev_net_notifier *nn;
 
-	list_for_each_entry(nn, &dev->net_notifier_list, list) {
-		__unregister_netdevice_notifier_net(dev_net(dev), nn->nb);
-		__register_netdevice_notifier_net(net, nn->nb, true);
-	}
+	list_for_each_entry(nn, &dev->net_notifier_list, list)
+		__move_netdevice_notifier_net(dev_net(dev), net, nn->nb);
 }
 
 /**