Mechanism driver API: responsible_for_rsc_provider

Allow mechanism manager to query drivers if they are responsible for a
resource provider or not.

Change-Id: Iea76d85c532b6bded2654062997738295ffc2f5b
Needed-By: https://review.openstack.org/574783
Partial-Bug: #1578989
See-Also: https://review.openstack.org/502306 (nova spec)
See-Also: https://review.openstack.org/508149 (neutron spec)

neutron_lib/plugins/ml2/api.py

@@ -413,6 +413,27 @@ class MechanismDriver(object):
         """
         return candidate_hosts
 
+    def responsible_for_ports_allocation(self, context):
+        """Is responsible for a port's resource provider?
+
+        :param context: PortContext instance describing the port
+        :returns: True for responsible, False for not responsible
+
+        For ports having an allocation in Placement (as expressed
+        in the port's binding:profile.allocation) decide while
+        binding if this mechanism driver is responsible for the
+        physical network interface represented by the resource
+        provider in Placement. Find the resource provider UUID in
+        context.current['binding:profile']['allocation'].
+
+        Drivers wanting to support resource allocations for ports in
+        Placement (eg. wanting to guarantee some minimum bandwidth)
+        must implement this method.
+
+        Default implementation returns False (backward compatibility).
+        """
+        return False
+
 
 @six.add_metaclass(abc.ABCMeta)
 class _TypeDriverBase(object):

releasenotes/notes/responsible_for_ports_allocation-5599dc59b3c98db2.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    New MechanismDriver API method: ``responsible_for_ports_allocation``.
+    Mechanism drivers wanting to support resource allocations for ports in
+    Placement (eg. wanting to guarantee some minimum bandwidth allocated
+    on the resource provider in the port's ``binding:profile.allocation``)
+    must implement this method. The default implementation reports not
+    being responsible for any resource providers, therefore unaffected
+    drivers need not be changed.