Comment 9 for bug 1531862

Reviewed: https://review.openstack.org/291042
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=7afbd3a6b896d6d1285343f31517e9a656cfa606
Submitter: Jenkins
Branch: master

commit 7afbd3a6b896d6d1285343f31517e9a656cfa606
Author: Kevin Benton <email address hidden>
Date: Wed Mar 9 23:47:35 2016 -0800

    Check tap bridge timestamps to detect local changes

    During a quick instance rebuild on Nova, it may remove a tap
    interface and then plug it in within the agent polling window.
    In this scenario the agent will not realize a device has changed
    and will therefore not ask the server for info an subsequently
    update its status. This will prevent the notification from being
    sent back to Nova that the vif plugging has finished so the
    VM will never resume state.

    This adds a new timestamp collection method to the common agent
    manager interface for devices that is used by the common agent
    loop to determine if a device has locally changed.

    The linux bridge implementation of it checks the timestamps on the
    tap interface's 'bridge' directory, which will change whenever
    the tap is added to bridge.

    Closes-Bug: #1531862
    Change-Id: If172470e907848556b6a8aff13520f94245919bb