Comment 6 for bug 1719362

Reviewed: https://review.openstack.org/507202
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ea9bf5216be60fb3fa1704cf6257adca4e634cb1
Submitter: Zuul
Branch: master

commit ea9bf5216be60fb3fa1704cf6257adca4e634cb1
Author: Matthew Booth <email address hidden>
Date: Mon Sep 25 17:32:14 2017 +0100

    libvirt: Don't VIR_MIGRATE_NON_SHARED_INC without migrate_disks

    If we specify block migration, but there are no disks which actually
    require block migration we call libvirt's migrateToURI3() with
    VIR_MIGRATE_NON_SHARED_INC in flags and an empty migrate_disks in
    params. Libvirt interprets this to be the default block migration
    behaviour of "block migrate all writeable disks". However,
    migrate_disks may only be empty because we filtered attached volumes
    out of it, in which case libvirt will block migrate attached volumes.
    This is a data corruptor.

    This change addresses the issue at the point we call migrateToURI3().
    As we never want the default block migration behaviour, we can safely
    remove the flag if the list of disks to migrate is empty.

    Change-Id: I9b545ca8aa6dd7b41ddea2d333190c9fbed19bc1
    Resolves-bug: #1719362