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 ea9bf5216b)
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.
(cherry picked from commit 2486f34ec4)
Change-Id: I9b545ca8aa6dd7b41ddea2d333190c9fbed19bc1
Resolves-bug: #1719362
2cfdb9c056