dev_change_net_namespace: send a KOBJ_REMOVED/KOBJ_ADD

When a new nic is created in namespace ns1, the kernel sends a KOBJ_ADD uevent to ns1. When the nic is moved to ns2, we only send a KOBJ_MOVE to ns2, and nothing to ns1.

This patch changes that behavior so that when moving a nic from ns1 to ns2, we send a KOBJ_REMOVED to ns1 and KOBJ_ADD to ns2. (The KOBJ_MOVE is still sent to ns2).

The effects of this can be seen when starting and stopping containers in an upstart based host. Lxc will create a pair of veth nics, the kernel sends KOBJ_ADD, and upstart starts network-instance jobs for each. When one nic is moved to the container, because no KOBJ_REMOVED event is received, the network-instance job for that veth never goes away. This was reported at https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1065589
With this patch the networ-instance jobs properly go away.

The other oddness solved here is that if a nic is passed into a running upstart-based container, without this patch no network-instance job is started in the container. But when the container creates a new nic itself (ip link add new type veth) then network-interface jobs are created. With this patch, behavior comes in line with a regular host.

v2: also send KOBJ_ADD to new netns. There will then be a _MOVE event from the device_rename() call, but that should be innocuous.

---
 net/core/dev.c |    6 ++++++
 1 file changed, 6 insertions(+)

index e2215ee..2c43aaf 100644
@@ -6172,6 +6172,9 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	dev_uc_flush(dev);
 	dev_mc_flush(dev);
 
+	/* Send a netdev-removed uevent to the old namespace */
+	kobject_uevent(&dev->dev.kobj, KOBJ_REMOVE);
+
 	/* Actually switch the network namespace */
 	dev_net_set(dev, net);
 

@@ -6183,6 +6186,9 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 			dev->iflink = dev->ifindex;
 	}
 
+	/* Send a netdev-add uevent to the new namespace */
+	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);
+
 	/* Fixup kobjects */
 	err = device_rename(&dev->dev, dev->name);
 	WARN_ON(err);

1.7.9.5

From: Serge Hallyn <[email protected]>
Date: Mon, 3 Dec 2012 20:17:12 -0600

Applied, thanks.