Revert "Change list of available qos rules"

This reverts commit 3299cdffae.

At least, there's a user which relies on the previous
semantics. (Our tempest plugin)
We should not change API semantics lightly
in an incompatible way.

Closes-Bug: #1694396
Related-Bug: #1694190
Change-Id: I88a216951d8996ac8bc90078b4239f0d25392e58

doc/source/devref/quality_of_service.rst

@@ -101,14 +101,12 @@ For a list of all rule types, see:
 neutron.services.qos.qos_consts.VALID_RULE_TYPES.
 
 The list of supported QoS rule types exposed by neutron is calculated as
-set of rules supported by at least one active QoS driver.
+the common subset of rules supported by all active QoS drivers.
 
 Note: the list of supported rule types reported by core plugin is not enforced
-when accessing QoS rule resources.
-
-When a policy is attached to a port or a network, or when a rule is created or updated,
-core plugins may validate write requests against their backends, and invalidate requests
-that don't make sense or can't be implemented by affected backends.
+when accessing QoS rule resources. This is mostly because then we would not be
+able to create rules while at least one of the QoS driver in gate lacks
+support for the rules we're trying to test.
 
 
 Database models

neutron/services/qos/drivers/manager.py

@@ -142,14 +142,20 @@ class QosServiceDriverManager(object):
         if not self._drivers:
             return []
 
-        rule_types = set()
+        rule_types = set(qos_consts.VALID_RULE_TYPES)
 
         # Recalculate on every call to allow drivers determine supported rule
         # types dynamically
         for driver in self._drivers:
-            rule_types |= set(driver.supported_rules)
+            new_rule_types = rule_types & set(driver.supported_rules)
+            dropped_rule_types = rule_types - new_rule_types
+            if dropped_rule_types:
+                LOG.debug("%(rule_types)s rule types disabled "
+                          "because enabled %(driver)s does not support them",
+                          {'rule_types': ', '.join(dropped_rule_types),
+                           'driver': driver.name})
+            rule_types = new_rule_types
 
         LOG.debug("Supported QoS rule types "
-                  "(rules supported by at least one loaded QoS driver): %s",
-                  rule_types)
+                  "(common subset for all loaded QoS drivers): %s", rule_types)
         return rule_types

neutron/tests/unit/services/qos/drivers/test_manager.py

@@ -144,7 +144,7 @@ class TestQoSDriversRulesValidations(TestQosDriversManagerBase):
 
 class TestQosDriversManagerRules(TestQosDriversManagerBase):
     """Test supported rules"""
-    def test_available_rules(self):
+    def test_available_rules_one_in_common(self):
         driver_manager = self._create_manager_with_drivers({
             'driver-A': {
                 'is_loaded': True,
@@ -176,9 +176,35 @@ class TestQosDriversManagerRules(TestQosDriversManagerBase):
             }
         })
         self.assertEqual(driver_manager.supported_rule_types,
-                         set([qos_consts.RULE_TYPE_BANDWIDTH_LIMIT,
-                              qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH,
-                              qos_consts.RULE_TYPE_DSCP_MARKING]))
+                         set([qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH]))
+
+    def test_available_rules_no_rule_in_common(self):
+        driver_manager = self._create_manager_with_drivers({
+            'driver-A': {
+                'is_loaded': True,
+                'rules': {
+                    qos_consts.RULE_TYPE_BANDWIDTH_LIMIT: {
+                        "max_kbps": {'type:values': None},
+                        "max_burst_kbps": {'type:values': None}
+                    }
+                }
+            },
+            'driver-B': {
+                'is_loaded': True,
+                'rules': {
+                    qos_consts.RULE_TYPE_MINIMUM_BANDWIDTH: {
+                        "min_kbps": {'type:values': None},
+                        'direction': {
+                            'type:values': constants.VALID_DIRECTIONS}
+                    },
+                    qos_consts.RULE_TYPE_DSCP_MARKING: {
+                        "dscp_mark": {
+                            'type:values': constants.VALID_DSCP_MARKS}
+                    }
+                }
+            }
+        })
+        self.assertEqual(driver_manager.supported_rule_types, set([]))
 
 
 class TestQosDriversCalls(TestQosDriversManagerBase):

releasenotes/notes/qos-change-list-of-available-rule-types-5ddbc827606c293d.yaml

@@ -1,7 +0,0 @@
----
-features:
-  - |
-    With `improved validation for QoS rules
-    <http://specs.openstack.org/openstack/neutron-specs/pike/qos-improved-validation-mechanism-rules.html>`_
-    API call to /v2.0/qos/rule-types now returns rule types that are supported
-    by at least one of enabled backends.