Comment 20 for bug 1489581

Reviewed: https://review.openstack.org/241270
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a084dbf9f07de2ea903ccd8aa84c60013aaa4193
Submitter: Jenkins
Branch: master

commit a084dbf9f07de2ea903ccd8aa84c60013aaa4193
Author: Matt Riedemann <email address hidden>
Date: Tue Nov 3 08:08:07 2015 -0800

    Add debug logging for when boot sequence is invalid in _validate_bdm

    The cells job is failing to boot from volume with a bdm v2 request like:

    "block_device_mapping_v2": [{
        "destination_type": "volume",
        "boot_index": 0,
        "uuid": "553083ac-40f2-4225-ac4d-a1d021eb7fb1",
        "source_type": "volume",
        "delete_on_termination": true
    }]

    Given it seems there should only be one BDM in the list and it's boot
    index is 0, we shouldn't fail on the boot sequence validation, so add
    some debug logging when we hit that failure.

    Also copy some wording out of the 'Block Device Mapping in Nova' section
    of the devref to add as code comments for the validation happening so we
    have context.

    TODO(mriedem): track down ndipanov to figure out why _subsequent_list
    omits the last element of the list that it's processing, we need to doc
    that logic in the code for maintainability.

    Change-Id: I8adc94f3c93c149689fbef424665fb44ac573819
    Related-Bug: #1489581