Comment 16 for bug 1662867

Reviewed: https://review.openstack.org/571432
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e0c7d6c8816d0c21b2913adc7a3d6cbd59604cd0
Submitter: Zuul
Branch: stable/ocata

commit e0c7d6c8816d0c21b2913adc7a3d6cbd59604cd0
Author: Matt Riedemann <email address hidden>
Date: Wed Mar 14 16:43:22 2018 -0400

    libvirt: handle DiskNotFound during update_available_resource

    The update_available_resource periodic task in the compute manager
    eventually calls through to the resource tracker and virt driver
    get_available_resource method, which gets the guests running on
    the hypervisor, and builds up a set of information about the host.
    This includes disk information for the active domains.

    However, the periodic task can race with instances being deleted
    concurrently and the hypervisor can report the domain but the driver
    has already deleted the backing files as part of deleting the
    instance, and this leads to failures when running "qemu-img info"
    on the disk path which is now gone.

    When that happens, the entire periodic update fails.

    This change simply tries to detect the specific failure from
    'qemu-img info' and translate it into a DiskNotFound exception which
    the driver can handle. In this case, if the associated instance is
    undergoing a task state transition such as moving to another host or
    being deleted, we log a message and continue. If the instance is in
    steady state (task_state is not set), then we consider it a failure
    and re-raise it up.

    Note that we could add the deleted=False filter to the instance query
    in _get_disk_over_committed_size_total but that doesn't help us in
    this case because the hypervisor says the domain is still active
    and the instance is not actually considered deleted in the DB yet.

    Conflicts:
            nova/virt/libvirt/driver.py
            nova/tests/unit/virt/libvirt/test_driver.py

    NOTE(lyarwood): Conflicts due to the substantial refactoring of
    _get_instance_disk_info via I9616a602ee0605f7f1dc1f47b6416f01895e025b
    and removal of _LW etc during Pike,

    Change-Id: Icec2769bf42455853cbe686fb30fda73df791b25
    Closes-Bug: #1662867
    (cherry picked from commit 5f16e714f58336344752305f94451e7c7c55742c)
    (cherry picked from commit 5a4c6913a37f912489543abd5e12a54feeeb89e2)
    (cherry picked from commit d251b95083731829ba104dc5c7f642dd5097d510)