custom mtu is not propergated correctly in openvswitch environments

[Michael Witt]

When using neutron with the openvswitch network driver and GRE tunneling it is ofter required to reduce the network device MTU to avoid ethernet frames becoming to big because of the GRE tunneling information that are appended.

When setting a network device MTU in nova.conf (option network_device_mtu) - this setting is only propagated to tapXXX device but not to the nsXXX device in the newly created IP Namespace.

We got this problem solved by adding the following lines to vifs.py in the attach function inside the try block:

            # Setup MTU on if_remote_name is required if it is a non default value
            mtu = CONF.network_device_mtu

            if vif.get('mtu') is not None:
                mtu = vif.get('mtu')

            if mtu is not None:
                utils.execute('ip', 'netns', 'exec', container_id, 'ip', 'link',
                              'set', if_remote_name, 'mtu', mtu, run_as_root=True)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/213612

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/213612
Committed: https://git.openstack.org/cgit/stackforge/nova-docker/commit/?id=3b3a0c744de288ef3477c6b2940e6308357777f2
Submitter: Jenkins
Branch: master

commit 3b3a0c744de288ef3477c6b2940e6308357777f2
Author: zhangguoqing <[e-mail]>
Date: Mon Aug 17 14:26:56 2015 +0800

    vif: Setup MTU on if_remote_name when attach

    If vif has the attribute mtu or the network_device_mtu which
    in nova.conf is not default value(None), we should setuping MTU
    on if_remote_name.

    Co-Authored-By: Michael Witt <email address hidden>

    Change-Id: I1dfa7272ed8ddd5f8c9b331992c9019402991c81
    Closes-bug: #1484415