Comment 3 for bug 1837756

Reviewed: https://review.opendev.org/672559
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=743dc083bb5628554d9abfa82665738233ed47e9
Submitter: Zuul
Branch: master

commit 743dc083bb5628554d9abfa82665738233ed47e9
Author: Matt Riedemann <email address hidden>
Date: Wed Jul 24 16:22:52 2019 +0000

    Revert "[libvirt] Filter hypervisor_type by virt_type"

    This reverts commit eaa766ee2093c24fd61c61e52f46bdd9ff9e93d2.

    The change regressed the behavior of the ImagePropertiesFilter
    because existing images with hypervisor_type=QEMU, which would
    match what is reported for hypervisor_type in the API for both
    qemu/kvm virt_type nodes, will now get filtered out for hosts
    where the configured virt_type is kvm.

    Note that both the ImagePropertiesFilter docs [1] and
    hypervisor_type image property docs [2] mention that for both
    qemu and kvm nodes the value to use is qemu since that is the
    actual hypervisor.

    Presumably the change was made for a deployment with some
    hosts configured with virt_type=qemu and other hosts configured
    with virt_type=kvm and there were separate images with
    hypervisor_type=qemu and hypervisor_type=kvm to match those hosts
    for scheduler filter, but as noted this was a regression in
    behavior for something that could have been achieved using
    host aggregates and the AggregateImagePropertiesIsolation filter.

    We could even use traits and a placement request pre-filter these
    days for a more modern approach.

    Also, since the API continues to report hypervisor_type=QEMU it's
    doubly confusing for operators to have to configure their images
    to use hypervisor_type=kvm (despite the docs).

    And finally, any existing instances which have hypervisor_type=qemu
    embedded in their RequestSpec can no longer be migrated to kvm
    hosts without manually fixing the entries in the request_specs
    table in the API DB.

    Note that this is not a clean revert because of change
    I5d95bd50279a6bf903a5793ad5f3ae9d06f085f4 made in Stein.

    [1] https://docs.openstack.org/nova/latest/admin/configuration/schedulers.html#imagepropertiesfilter
    [2] https://docs.openstack.org/glance/latest/admin/useful-image-properties.html

    Change-Id: I7d761dc269f8c12c4a76ba14201ccdd82a04d01d
    Closes-Bug: #1837756