Comment 98 for bug 1890501

Reviewed: https://review.opendev.org/747978
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2faf17995dd9daa6f0b91e44be43264e447c678d
Submitter: Zuul
Branch: stable/pike

commit 2faf17995dd9daa6f0b91e44be43264e447c678d
Author: Lee Yarwood <email address hidden>
Date: Wed Aug 5 23:00:06 2020 +0100

    libvirt: Provide VIR_MIGRATE_PARAM_PERSIST_XML during live migration

    The VIR_MIGRATE_PARAM_PERSIST_XML parameter was introduced in libvirt
    v1.3.4 and is used to provide the new persistent configuration for the
    destination during a live migration:

    https://libvirt.org/html/libvirt-libvirt-domain.html#VIR_MIGRATE_PARAM_PERSIST_XML

    Without this parameter the persistent configuration on the destination
    will be the same as the original persistent configuration on the source
    when the VIR_MIGRATE_PERSIST_DEST flag is provided.

    As Nova does not currently provide the VIR_MIGRATE_PARAM_PERSIST_XML
    param but does provide the VIR_MIGRATE_PERSIST_DEST flag this means that
    a soft reboot by Nova of the instance after a live migration can revert
    the domain back to the original persistent configuration from the
    source.

    Note that this is only possible in Nova as a soft reboot actually
    results in the virDomainShutdown and virDomainLaunch libvirt APIs being
    called that recreate the domain using the persistent configuration.
    virDomainReboot does not result in this but is not called at this time.

    The impact of this on the instance after the soft reboot is pretty
    severe, host devices referenced in the original persistent configuration
    on the source may not exist or could even be used by other users on the
    destination. CPU and NUMA affinity could also differ drastically between
    the two hosts resulting in the instance being unable to start etc.

    As MIN_LIBVIRT_VERSION is now > v1.3.4 this change simply includes the
    VIR_MIGRATE_PARAM_PERSIST_XML param using the same updated XML for the
    destination as is already provided to VIR_MIGRATE_PARAM_DEST_XML.

    Conflicts:
        nova/tests/unit/virt/libvirt/test_driver.py
        nova/virt/libvirt/driver.py

    NOTE(melwitt): Conflicts in driver.py are because changes:

      I6ac601e633ab2b0a67b4802ff880865255188a93
        (libvirt: Provide VGPU inventory for a single GPU type)
      I947bf0ad34a48e9182a3dc016f47f0c9f71c9d7b
        ([libvirt] Allow multiple volume attachments)
      Ibfa64f18bbd2fb70db7791330ed1a64fe61c1355
        (libvirt: QEMU native LUKS decryption for encrypted volumes)
      If2035cac931c42c440d61ba97ebc7e9e92141a28
        (libvirt: Rework 'EBUSY' (SIGKILL) error handling code path)
      Ibf210dd27972fed2651d6c9bd73a0bcf352c8bab
        (libvirt: create vGPU for instance)

    are not in Pike. Conflict in test_driver.py is because the Pike
    backport of change I9b545ca8aa6dd7b41ddea2d333190c9fbed19bc1 explicitly
    asserts byte string destination_xml in
    _test_live_migration_block_migration_flags and the change is not in
    Queens where this is being backported from.

    Co-authored-by: Tadayoshi Hosoya <email address hidden>
    Closes-Bug: #1890501
    Change-Id: Ia3f1d8e83cbc574ce5cb440032e12bbcb1e10e98
    (cherry picked from commit 1bb8ee95d4c3ddc3f607ac57526b75af1b7fbcff)
    (cherry picked from commit bbf9d1de06e9991acd968fceee899a8df3776d60)
    (cherry picked from commit 6a07edb4b29d8bfb5c86ed14263f7cd7525958c1)
    (cherry picked from commit b9ea91d17703f5b324a50727b6503ace0f4e95eb)
    (cherry picked from commit c438fd9a0eb1903306a53ab44e3ae80660d8a429)
    (cherry picked from commit a721ca5f510ce3c8ef24f22dac9e475b3d7651db)