DB consistency: lack of full security group information when notify precommit message of security group creating

For some mechanism drivers, it is important to know the full information of a newly created security group in pre commit message including security group id and default rules. The reason is that, some mechanism drivers should write every operations on a journal table to sync neutron operations to their own south-bound controller. In order to ensure ACID, they must sync into journal table in the pre commit phase instead post commit phase. However, the whole information only can be known in post commit message of security group creation. So, we should enrich such information in the pre commit message.

Related code:
    def create_security_group(self, context, security_group, default_sg=False):
        """Create security group.
        If default_sg is true that means we are a default security group for
        a given tenant if it does not exist.
        """
        s = security_group['security_group']
        kwargs = {
            'context': context,
            'security_group': s,
            'is_default': default_sg,
        }

        self._registry_notify(resources.SECURITY_GROUP, events.BEFORE_CREATE,
                              exc_cls=ext_sg.SecurityGroupConflict, **kwargs)

        tenant_id = s['tenant_id']

        if not default_sg:
            self._ensure_default_security_group(context, tenant_id)

        with db_api.autonested_transaction(context.session):
            security_group_db = sg_models.SecurityGroup(id=s.get('id') or (
                                              uuidutils.generate_uuid()),
                                              description=s['description'],
                                              tenant_id=tenant_id,
                                              name=s['name'])
            context.session.add(security_group_db)
            if default_sg:
                context.session.add(sg_models.DefaultSecurityGroup(
                    security_group=security_group_db,
                    tenant_id=security_group_db['tenant_id']))
            for ethertype in ext_sg.sg_supported_ethertypes:
                if default_sg:
                    # Allow intercommunication
                    ingress_rule = sg_models.SecurityGroupRule(
                        id=uuidutils.generate_uuid(), tenant_id=tenant_id,
                        security_group=security_group_db,
                        direction='ingress',
                        ethertype=ethertype,
                        source_group=security_group_db)
                    context.session.add(ingress_rule)

                egress_rule = sg_models.SecurityGroupRule(
                    id=uuidutils.generate_uuid(), tenant_id=tenant_id,
                    security_group=security_group_db,
                    direction='egress',
                    ethertype=ethertype)
                context.session.add(egress_rule)

            self._registry_notify(resources.SECURITY_GROUP,
                                  events.PRECOMMIT_CREATE,
                                  exc_cls=ext_sg.SecurityGroupConflict,
                                  **kwargs)

        secgroup_dict = self._make_security_group_dict(security_group_db)

        kwargs['security_group'] = secgroup_dict
        registry.notify(resources.SECURITY_GROUP, events.AFTER_CREATE, self,
                        **kwargs)
        return secgroup_dict

https://github.com/openstack/neutron/blob/master/neutron/db/securitygroups_db.py#L121