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[Chris Friesen <chris.friesen@xxxxxxxxxxxxx>]

The review for the oslo.versionedobjects change is here:
https://review.openstack.org/#/c/355981/

** Changed in: nova
       Status: New => Fix Released

** Project changed: nova => oslo.versionedobjects

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https://bugs.launchpad.net/bugs/1613488

Title:
  changed fields of versionedobjects not tracked properly when down-
  versioning object

Status in oslo.versionedobjects:
  Fix Released

Bug description:
  Sorry for the complicated write-up below, but the issue is
  complicated.

  
  I'm running into a problem between Mitaka and Kilo, but I *think* it'll also hit Mitaka/Liberty.  The problem scenario is when we have older and newer services talking to each other.  The problem occurs when nova-conductor writes to an object field that is removed in obj_make_compatible().  In particular, I'm hitting this with 'parent_addr' in the PciDevice class since it gets written in PciDevice._from_db_object().

  In oslo_versionedobjects/base.py the remotable() function has the following line:
  	self._changed_fields = set(updates.get('obj_what_changed', []))

  This blindly sets the local self._changed_fields to be whatever the
  remote end sent as updates['obj_what_changed'].

  This is a problem because the far end can include fields that don't
  actually exist in the older object version.  On the far end (which may
  be newer) in nova.conductor.manager.ConductorManager.object_action(),
  we will call the following (where 'objinst' is the current version of
  the object):

          updates['obj_what_changed'] = objinst.obj_what_changed()

  Since this is called against the newer object code, it can specify
  fields that do not exist in the older version of the object if nova-
  conductor has written those fields.

  The only workaround I've been able to come up with for this is to
  modify oslo_versionedobjects.base.remotable() to only include a field
  in self._changed_fields if it's in self.fields.  This requires
  updating the older code prior to an upgrade, however.

  
  I think there's another related issue.  In VersionedObject.obj_to_primitive() we set the changes in the primitive like this:

          if self.obj_what_changed():
              obj[self._obj_primitive_key('changes')] = list(
                  self.obj_what_changed())

  Since we call self.obj_what_changed() on the newer version of the
  object, I think we will include changes to fields that were removed by
  obj_make_compatible_from_manifest().

  It seems to me that in obj_to_primitive() we should not allow fields
  to be included in obj[self._obj_primitive_key('changes')] unless
  they're also listed in obj[self._obj_primitive_key('data')].

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