libvirt lxc needs iptables checksum added for dhcp packets

[Scott Moser]

I tested a devstack today with libvirt-lxc, and was unable to get a dhcp address in cirros 0.3.2.

The reason is that cirros's udhcpc seems to ignore the response if it doesn't have checksums.

the appropriate mangle rule would be written if /dev/vhost-net , but with newer kernels this is also happening on the lxc network devices.

It seems the sane thing to do at this point is just to drop the protection based on '/dev/vhost-net' presence.

--
Related bugs:
 * https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/930962
 * https://bugzilla.redhat.com/show_bug.cgi?id=910619#c6

[Scott Moser (smoser)]

https://review.openstack.org/#/c/103193/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/103193
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=0ca33df5660849ce305f9e9756007d95fcbbfa2b
Submitter: Jenkins
Branch: master

commit 0ca33df5660849ce305f9e9756007d95fcbbfa2b
Author: Scott Moser <email address hidden>
Date: Fri Jun 27 12:39:28 2014 -0400

    add checksums to udp independent of /dev/vhost-net.

    In newer kernel versions, the network devices added for lxc containers
    do not get checksums added. The result is the same as previously
    occurred when vhost-net became prevalent in kvm guests.

    Software that expects the checksums on packets will ignore them. One example
    of such software is udhcpc in cirros. Without this change, cirros containers
    in 3.13 kernels (Ubuntu 14.04) will fail to acquire an address via dhcp.

    Closes-Bug: #1335193
    Change-Id: Iba305fb7f8236955ca732e467db9e424535be93d