As explained in the comments, this patch lets the OCI runtime create the
netns when userns are in use. This is needed because the netns needs to
be owned by the userns (otherwise can't modify the IP, etc.).
Before this patch, we are creating the netns and then starting the pod
sandbox asking to join this netns. This can't never work with userns, as
the userns needs to be created first for the netns ownership to be
correct.
One option would be to also create the userns in containerd, then create
the netns. But this is painful (needs tricks with the go runtime,
special care to write the mapping, etc.).
So, we just let the OCI runtime create the userns and netns, that
creates them with the proper ownership.
As requested by Mike Brown, the current code when userns is not used is
left unchanged. We can unify the cases (with and without userns) in a
future release.
Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>
