code: func toHost(contID int, idMap []IDMap) (int, error) {
  	if idMap == nil {
  		return contID, nil
  	}
  	for _, m := range idMap {
  		if (contID >= m.ContainerID) && (contID <= (m.ContainerID + m.Size - 1)) {
  			hostID := m.HostID + (contID - m.ContainerID)
  			return hostID, nil
  		}
  	}
  	return -1, fmt.Errorf("Container ID %d cannot be mapped to a host ID", contID)
  }
docs: // toHost takes an id mapping and a remapped ID, and translates the
  // ID to the mapped host ID. If no map is provided, then the translation
  // assumes a 1-to-1 mapping and returns the passed in id #