private Set<String> sourceOsFamilies(UpgradeCheckRequest request) throws AmbariException {
    StackId stackId = new StackId(request.getTargetRepositoryVersion().getStackId());
    return ambariMetaInfo.get().getStack(stackId).getRepositoriesByOs().keySet();
  }
@return set of each os family in the source stack
ambari-server/src/main/java/org/apache/ambari/server/checks/MissingOsInRepoVersionCheck.java