Comment 9 for bug 1719362

Reviewed: https://review.openstack.org/519632
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2486f34ec49ffdf381912d7f0fd5199ce0dfa013
Submitter: Zuul
Branch: stable/pike

commit 2486f34ec49ffdf381912d7f0fd5199ce0dfa013
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.

    (cherry picked from commit ea9bf5216be60fb3fa1704cf6257adca4e634cb1)

    nova/tests/unit/virt/libvirt/test_driver.py:
      Explicitly asserts byte string destination_xml in
      _test_live_migration_block_migration_flags. Not required in master
      due to change I85cd9a90.

    Change-Id: I9b545ca8aa6dd7b41ddea2d333190c9fbed19bc1
    Resolves-bug: #1719362