netdev - [patch net 1/3] net: allow to ask per-net netdevice notifier to follow netdev dynamically

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Message-Id: <20230509100939.760867-2-jiri@resnulli.us>
Date: Tue,  9 May 2023 12:09:37 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: netdev@...r.kernel.org
Cc: kuba@...nel.org,
	pabeni@...hat.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	jacob.e.keller@...el.com,
	saeedm@...dia.com,
	moshe@...dia.com
Subject: [patch net 1/3] net: allow to ask per-net netdevice notifier to follow netdev dynamically

From: Jiri Pirko <jiri@...dia.com>

Currently, it is possible to register netdev notifier to get only
events related to a selected namespace. This could be done by:
register_netdevice_notifier_net()

Another extension which currently exists is to register netdev notifier
that receives events related to a namespace, where a netdev is. The
notifier moves from namespace to namespace with the selected netdev.
This could be done by:
register_netdevice_notifier_dev_net()

Devlink has a usecase to monitor a namespace and whenever certain netdev
appears in this namespace, it needs to get notifications even in case
netdev moves to a different namespace. It's basically a combination of
the two described above.

Introduce a pair of functions netdev_net_notifier_follow() and
netdev_net_notifier_unfollow() to be called on previously registered
per-net notifier asking to follow the given netdev.

Signed-off-by: Jiri Pirko <jiri@...dia.com>
---
 include/linux/netdevice.h |  6 ++++++
 net/core/dev.c            | 34 +++++++++++++++++++++++++++++-----
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 08fbd4622ccf..63376dad8464 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2890,6 +2890,12 @@ 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 netdev_net_notifier_follow(struct net_device *dev,
+				struct notifier_block *nb,
+				struct netdev_net_notifier *nn);
+void netdev_net_notifier_unfollow(struct net_device *dev,
+				  struct netdev_net_notifier *nn,
+				  struct net *net);
 int register_netdevice_notifier_dev_net(struct net_device *dev,
 					struct notifier_block *nb,
 					struct netdev_net_notifier *nn);
diff --git a/net/core/dev.c b/net/core/dev.c
index 735096d42c1d..3458ed8f98f2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1868,6 +1868,32 @@ static void __move_netdevice_notifier_net(struct net *src_net,
 	__register_netdevice_notifier_net(dst_net, nb, true);
 }
 
+void netdev_net_notifier_follow(struct net_device *dev,
+				struct notifier_block *nb,
+				struct netdev_net_notifier *nn)
+{
+	ASSERT_RTNL();
+	nn->nb = nb;
+	list_add(&nn->list, &dev->net_notifier_list);
+}
+EXPORT_SYMBOL(netdev_net_notifier_follow);
+
+static void __netdev_net_notifier_unfollow(struct netdev_net_notifier *nn)
+{
+	list_del(&nn->list);
+}
+
+void netdev_net_notifier_unfollow(struct net_device *dev,
+				  struct netdev_net_notifier *nn,
+				  struct net *net)
+{
+	ASSERT_RTNL();
+	__netdev_net_notifier_unfollow(nn);
+	if (!net_eq(dev_net(dev), net))
+		__move_netdevice_notifier_net(dev_net(dev), net, nn->nb);
+}
+EXPORT_SYMBOL(netdev_net_notifier_unfollow);
+
 int register_netdevice_notifier_dev_net(struct net_device *dev,
 					struct notifier_block *nb,
 					struct netdev_net_notifier *nn)
@@ -1876,10 +1902,8 @@ int register_netdevice_notifier_dev_net(struct net_device *dev,
 
 	rtnl_lock();
 	err = __register_netdevice_notifier_net(dev_net(dev), nb, false);
-	if (!err) {
-		nn->nb = nb;
-		list_add(&nn->list, &dev->net_notifier_list);
-	}
+	if (!err)
+		netdev_net_notifier_follow(dev, nb, nn);
 	rtnl_unlock();
 	return err;
 }
@@ -1892,7 +1916,7 @@ int unregister_netdevice_notifier_dev_net(struct net_device *dev,
 	int err;
 
 	rtnl_lock();
-	list_del(&nn->list);
+	__netdev_net_notifier_unfollow(nn);
 	err = __unregister_netdevice_notifier_net(dev_net(dev), nb);
 	rtnl_unlock();
 	return err;
-- 
2.39.2