Comment 19 for bug 1794364

Reviewed: https://review.openstack.org/611463
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=d47486d317e8cdb1cdab50d73f6484289ab082d4
Submitter: Zuul
Branch: master

commit d47486d317e8cdb1cdab50d73f6484289ab082d4
Author: imacdonn <email address hidden>
Date: Wed Oct 17 22:48:18 2018 +0000

    cinder-manage online_data_migrations fixes

    Addresses some issues with this command:

    1) When used without the --max-count option, the summary table will
       always show zero migrations run, because it only accounts for the
       last batch, and the loop only exits when the last batch does no work.

    2) "remaining" counts cannot be accurate, given the way migrations are
       implemented, because the "found" count refers to the number of rows
       that exist in the database, not the number that still need the
       migration applied.

    3) In the case where no migrations are successful, but some raise
       exceptions, the command was exiting with status zero, which usually
       indicates "success". This can cause issues that cause migration
       failures to go unnoticed, especially when automated.

    4) When exceptions do occur, a minimally useful message is output, and
       no detail about the exception is available to the user. The exception
       detail should be logged.

    5) Inaccuracies in the documentation - "--max_number" should be
       "--max-count", and stale references to the "--ignore_state" option,
       which was removed in [1]

    The solution for (3) introduces a new exit status, 2. See release note
    for details.

    These changes are aligned with equivalents [2][3] for the nova-manage
    command, except for the calculation of "Total Needed" - nova seems to
    interpret the "found" count differently/inconsistently.

    [1] https://review.openstack.org/510201
    [2] https://review.openstack.org/605828
    [3] https://review.openstack.org/608091

    Change-Id: I878480eb2359625cde839b073230844acc645cba
    Closes-Bug: #1794364
    Closes-Bug: #1796192