text: # Copyright (c) 2012 OpenStack Foundation
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  from oslo_log import log as logging
  
  from nova.scheduler import filters
  
  LOG = logging.getLogger(__name__)
  
  
  class RetryFilter(filters.BaseHostFilter):
      """Filter out nodes that have already been attempted for scheduling
      purposes
      """
  
      def host_passes(self, host_state, filter_properties):
          """Skip nodes that have already been attempted."""
          retry = filter_properties.get('retry', None)
          if not retry:
              # Re-scheduling is disabled
              LOG.debug("Re-scheduling is disabled")
              return True
  
          hosts = retry.get('hosts', [])
          host = [host_state.host, host_state.nodename]
  
          passes = host not in hosts
  
          if not passes:
              LOG.debug("Host %(host)s fails.  Previously tried hosts: "
                          "%(hosts)s", {'host': host, 'hosts': hosts})
  
          # Host passes if it's not in the list of previously attempted hosts:
          return passes
  