uevent when moving nic between network namespaces?

Eric W. Biederman ebiederm at xmission.com
Fri Oct 12 03:26:46 UTC 2012

Serge Hallyn <serge.hallyn at canonical.com> writes:

> Hi,
> Dan Kegel (cc:d) found an interesting nuisance relating to upstart
> and network interfaces with lxc containers.  In particular, when you
> start a container, two veths are created.  A uevent for their creation
> is sent, and so a 'network-interface' upstart job is created for each.
> One of the veths is passed into the container.  When the container
> shuts down, the veth in the init-net-ns gets a net-device-removed
> uevent, so the network-interface upstart job goes away.  But the veth
> in the container doesn't cause a net-device-removed upstart uevent
> to be sent.  So its network-interface upstart job sticks around.
> The details are at:
> https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1065589
> I notice that when simply renaming a netdev (sudo ip link set veth1 name
> veth2) then udevadm monitor shows:
> KERNEL[17945.234850] move     /devices/virtual/net/veth2 (net)
> UDEV  [17945.235758] move     /devices/virtual/net/veth2 (net)
> but when I do 'sudo ip link set veth2 netns 27689' then 'udevadm
> monitor' shows nothing.
> When I do
> 	sudo ip link set veth1 netns 32296
> 	(in process 32296) sudo ip link set veth1 name veth2
> then, again udevadm monitor shows nothing.
> So the question is, should the kernel be sending uevents for
> net-device-removed and then net-device-added when a nic is moved
> between network namespaces?  Or should lxc just fake that?

To the best of my memory I wired up those events, and they should be
delivered.  Now they uevents will only be delivered in the relevant
network namespace.

Hmm.  But the relevant code in the kernel is device_rename, and it
happens after we switch the network namespace on the device.

Which probably means that in practice only the new network namespace is
seeing uevents.



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