code: void reloadWhitelist() throws IOException {
  
      // read the entire whitelist into memory outside the
      // FSNamessytem lock.
      //
      LinkedList<String> paths = new LinkedList<String>();
      FileInputStream fstream = new FileInputStream(whitelistFile);
      DataInputStream in = new DataInputStream(fstream);
      BufferedReader br = new BufferedReader(new InputStreamReader(in));
      int count = 0;
      while (true) {
        String str = br.readLine();
        if (str == null) {
          break;                  // end of file
        }
        str = str.trim();         // remove all whitespace from start and end
        if (str.startsWith("#")) {
          continue;               // ignore lines with starting with #
        }
        paths.add(str);
        LOG.info("Whitelisted directory [" + count + "] " + str);
        count++;
      }
      in.close();
  
      // acquire the writelock and insert newly read entries into 
      // the Namenode's configuration.
      namesys.writeLock();
      try {
        namesys.neverDeletePaths.clear();
        for (String s: paths) {
          namesys.neverDeletePaths.add(s);
        }
      } finally {
        namesys.writeUnlock();
      }
    }
docs: Removes all the entries currently in neverDeletePaths
  and add the new ones specified