From facc4e94cae64b6c79cd4538e452e838436eac0f Mon Sep 17 00:00:00 2001
From: Bence Romsics <bence.romsics@ericsson.com>
Date: Mon, 11 Feb 2019 14:47:31 +0100
Subject: [PATCH] Reject QoS minimum bandwidth rule updates for bound ports as
 NotImplemented

Updating QoS policies and rules backed by resources tracked in Placement
is a complex task, which was left out of scope for the Stein release.
Of course this is only relevant for policies/rules already in use on
bound ports. Rules of unbound ports can still be updated freely.

Please note this patch cannot catch all possible problems. There will
always be a time window between the allocation committed to Placement
and Nova sending the port binding request to Neutron. If the policy or
rule is changed in this window we cannot do anything against it.

APIImpact: Reject QoS minimum bandwidth policy/rule updates for bound
           ports as NotImplemented

Change-Id: I477edb0ae35b385ac776a58195f22382e2fce4ed
Partial-Bug: #1578989
See-Also: https://review.openstack.org/502306 (nova spec)
See-Also: https://review.openstack.org/508149 (neutron spec)
---
 neutron/services/qos/qos_plugin.py            | 24 +++++++++++++++++++
 ...eject-min-bw-updates-30bd0e3201dafce1.yaml |  8 +++++++
 2 files changed, 32 insertions(+)
 create mode 100644 releasenotes/notes/reject-min-bw-updates-30bd0e3201dafce1.yaml

diff --git a/neutron/services/qos/qos_plugin.py b/neutron/services/qos/qos_plugin.py
index 4e1b4806841..11e3ae3d8c7 100644
--- a/neutron/services/qos/qos_plugin.py
+++ b/neutron/services/qos/qos_plugin.py
@@ -31,6 +31,7 @@ from neutron_lib.placement import constants as pl_constants
 from neutron_lib.placement import utils as pl_utils
 from neutron_lib.services.qos import constants as qos_consts
 
+from neutron._i18n import _
 from neutron.db import db_base_plugin_common
 from neutron.extensions import qos
 from neutron.objects import base as base_obj
@@ -226,6 +227,23 @@ class QoSPlugin(qos.QoSPluginBase):
                 raise qos_exc.QosRuleNotSupported(rule_type=rule.rule_type,
                                                   port_id=port['id'])
 
+    def reject_min_bw_rule_updates(self, context, policy):
+        ports = self._get_ports_with_policy(context, policy)
+        for port in ports:
+            # NOTE(bence romsics): In some cases the presence of
+            # 'binding:profile.allocation' is a more precise marker than
+            # 'device_owner' about when we have to reject min-bw related
+            # policy/rule updates. However 'binding:profile.allocation' cannot
+            # be used in a generic way here. Consider the case when the first
+            # min-bw rule is added to a policy having ports in-use. Those ports
+            # will not have 'binding:profile.allocation', but this policy
+            # update must be rejected.
+            if (port.device_owner is not None and
+                    port.device_owner.startswith('compute:')):
+                raise NotImplementedError(_(
+                    'Cannot update QoS policies/rules backed by resources '
+                    'tracked in Placement'))
+
     @db_base_plugin_common.convert_result_to_dict
     def create_policy(self, context, policy):
         """Create a QoS policy.
@@ -384,6 +402,8 @@ class QoSPlugin(qos.QoSPluginBase):
             rule.create()
             policy.obj_load_attr('rules')
             self.validate_policy(context, policy)
+            if rule.rule_type == qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH:
+                self.reject_min_bw_rule_updates(context, policy)
             self.driver_manager.call(qos_consts.UPDATE_POLICY_PRECOMMIT,
                                      context, policy)
 
@@ -424,6 +444,8 @@ class QoSPlugin(qos.QoSPluginBase):
             rule.update()
             policy.obj_load_attr('rules')
             self.validate_policy(context, policy)
+            if rule.rule_type == qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH:
+                self.reject_min_bw_rule_updates(context, policy)
             self.driver_manager.call(qos_consts.UPDATE_POLICY_PRECOMMIT,
                                      context, policy)
 
@@ -451,6 +473,8 @@ class QoSPlugin(qos.QoSPluginBase):
             rule = policy.get_rule_by_id(rule_id)
             rule.delete()
             policy.obj_load_attr('rules')
+            if rule.rule_type == qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH:
+                self.reject_min_bw_rule_updates(context, policy)
             self.driver_manager.call(qos_consts.UPDATE_POLICY_PRECOMMIT,
                                      context, policy)
 
diff --git a/releasenotes/notes/reject-min-bw-updates-30bd0e3201dafce1.yaml b/releasenotes/notes/reject-min-bw-updates-30bd0e3201dafce1.yaml
new file mode 100644
index 00000000000..f358c344f0a
--- /dev/null
+++ b/releasenotes/notes/reject-min-bw-updates-30bd0e3201dafce1.yaml
@@ -0,0 +1,8 @@
+---
+other:
+  - |
+    Neutron server now rejects (as ``NotImplementedError``) updates of
+    ``minimum_bandwidth`` QoS rules if the rule is already in effect on bound
+    ports. Implementing updates will require updates to Placement allocations
+    and possibly migrating servers where the new ``minimum_bandwidth`` can be
+    satisifed.