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.
Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>