Comment 15 for bug 1627134

Reviewed: https://review.openstack.org/387292
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a021a72ddaea0e1eb6e3f4b934870fd5f2a05485
Submitter: Jenkins
Branch: stable/newton

commit a021a72ddaea0e1eb6e3f4b934870fd5f2a05485
Author: Matthew Booth <email address hidden>
Date: Wed Sep 28 16:44:41 2016 +0100

    libvirt: Fix BlockDevice.wait_for_job when qemu reports no job

    We were misinterpreting the return value of blockJobInfo. Most
    immediately we were expecting it to return an integer, which has never
    been the case. blockJobInfo also raises an exception on error. Note
    that the implementation of abort_on_error has always expected an
    integer return value, and exceptions have never been handled, which
    means that abort_on_error has always been a no-op, and exceptions have
    never been swallowed. As this is also the most intuitive behaviour, we
    make it explicit by removing abort_on_error. Any exception raised by
    blockJobInfo will continue to propagate unhandled.

    We were obfuscating the return value indicating that the job did not
    exist, {}, by populating a BlockDeviceJobInfo with fake values. We
    de-obfuscate this by returning None instead, which is unambiguous.

    wait_for_job() was misnamed, as it does not wait. This is renamed to
    is_job_complete() to be less confusing. Note that the logic is
    reversed.

    After discussion with Eric Blake of the libvirt team (see review
    comments: https://review.openstack.org/#/c/375652/), we are now
    confident asserting that if no job exists then it has completed
    (although we are still not sure that it succeeded). Consequently we
    remove the wait_for_job_clean parameter, and always assume that no job
    means it has completed. Previously this was implicit because no job
    meant a defaulted BlockDeviceJobInfo.job value of 0.

    Co-authored-by: Sławek Kapłoński <email address hidden>
    Closes-Bug: #1627134
    Change-Id: I2d0daa32b1d37fa60412ad7a374ee38cebdeb579
    (cherry picked from commit 0f4bd241665c287e49f2d30ca79be96298217b7e)