Comment 56 for bug 1815989

Reviewed: https://review.opendev.org/c/openstack/nova/+/602432
Committed: https://opendev.org/openstack/nova/commit/a62dd42c0dbb6b2ab128e558e127d76962738446
Submitter: "Zuul (22348)"
Branch: master

commit a62dd42c0dbb6b2ab128e558e127d76962738446
Author: Stephen Finucane <email address hidden>
Date: Fri Apr 30 12:51:35 2021 +0100

    libvirt: Delegate OVS plug to os-vif

    os-vif 1.15.0 added the ability to create an OVS port during plugging
    by specifying the 'create_port' attribute in the 'port_profile' field.
    By delegating port creation to os-vif, we can rely on it's 'isolate_vif'
    config option [1] that will temporarily configure the VLAN to 4095
    (0xfff), which is reserved for implementation use [2] and is used by
    neutron to as a dead VLAN [3]. By doing this, we ensure VIFs are plugged
    securely, preventing guests from accessing other tenants' networks
    before the neutron OVS agent can wire up the port.

    This change requires a little dance as part of the live migration flow.
    Since we can't be certain the destination host has a version of os-vif
    that supports this feature, we need to use a sentinel to indicate when
    it does. Typically we would do so with a field in
    'LibvirtLiveMigrateData', such as the 'src_supports_numa_live_migration'
    and 'dst_supports_numa_live_migration' fields used to indicate support
    for NUMA-aware live migration. However, doing this prevents us
    backporting this important fix since o.vo changes are not backportable.
    Instead, we (somewhat evilly) rely on the free-form nature of the
    'VIFMigrateData.profile_json' string field, which stores JSON blobs and
    is included in 'LibvirtLiveMigrateData' via the 'vifs' attribute, to
    transport this sentinel. This is a hack but is necessary to work around
    the lack of a free-form "capabilities" style dict that would allow us do
    backportable fixes to live migration features.

    Note that this change has the knock on effect of modifying the XML
    generated for OVS ports: when hybrid plug is false will now be of type
    'ethernet' rather than 'bridge' as before. This explains the larger than
    expected test damage but should not affect users.

    [1] https://opendev.org/openstack/os-vif/src/tag/2.4.0/vif_plug_ovs/ovs.py#L90-L93
    [2] https://en.wikipedia.org/wiki/IEEE_802.1Q#Frame_format
    [3] https://answers.launchpad.net/neutron/+question/231806

    Change-Id: I11fb5d3ada7f27b39c183157ea73c8b72b4e672e
    Depends-On: Id12486b3127ab4ac8ad9ef2b3641da1b79a25a50
    Closes-Bug: #1734320
    Closes-Bug: #1815989