private ConfigUpgradePack parseConfigUpgradePack(File upgradeFile) throws AmbariException {
    ConfigUpgradePack pack = null;
    try {
      pack = unmarshaller.unmarshal(ConfigUpgradePack.class, upgradeFile);
    } catch (Exception e) {
      if (upgradeFile == null) {
        throw new AmbariException("Null config upgrade pack");
      }
      throw new AmbariException("Unable to parse stack upgrade file at location: " + upgradeFile.getAbsolutePath(), e);
    }
    return pack;
  }
Parse all stack upgrade files for the stack.

@param subDirs stack sub directories
@throws AmbariException if unable to parse stack upgrade file
ambari-server/src/main/java/org/apache/ambari/server/stack/StackDirectory.java