Comment 17 for bug 1845161

Reviewed: https://review.opendev.org/706909
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=6376391b45d6855705bd9a291996e3a4110ad26f
Submitter: Zuul
Branch: stable/stein

commit 6376391b45d6855705bd9a291996e3a4110ad26f
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Tue Oct 22 14:21:08 2019 +0000

    [OVS] Handle added/removed ports in the same polling iteration

    The OVS agent processes the port events in a polling loop. It could
    happen (and more frequently in a loaded OVS agent) that the "removed"
    and "added" events can happen in the same polling iteration. Because
    of this, the same port is detected as "removed" and "added".

    When the virtual machine is restarted, the port event sequence is
    "removed" and then "added". When both events are captured in the same
    iteration, the port is already present in the bridge and the port is
    discharted from the "removed" list.

    Because the port was removed first and the added, the QoS policies do
    not apply anymore (QoS and Queue registers, OF rules). If the QoS
    policy does not change, the QoS agent driver will detect it and won't
    call the QoS driver methods (based on the OVS agent QoS cache, storing
    port and QoS rules). This will lead to an unconfigured port.

    This patch solves this issue by detecting this double event and
    registering it as "removed_and_added". When the "added" port is
    handled, the QoS deletion method is called first (if needed) to remove
    the unneded artifacts (OVS registers, OF rules) and remove the QoS
    cache (port/QoS policy). Then the QoS policy is applied again on the
    port.

    NOTE: this is going to be quite difficult to be tested in a fullstack
    test.

    Conflicts:
          neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py

    Change-Id: I51eef168fa8c18a3e4cee57c9ff86046ea9203fd
    Closes-Bug: #1845161
    (cherry picked from commit 50ffa5173db03b0fd0fe7264e4b2a905753f86ec)
    (cherry picked from commit 3eceb6d2ae5523a2658906cc086ea98e1be3209a)