code: public BlockLocation[] getFileBlockLocations(FileStatus file, 
        long start, long len) throws IOException {
      if (file == null) {
        return null;
      }
  
      if ( (start<0) || (len < 0) ) {
        throw new IllegalArgumentException("Invalid start or len parameter");
      }
  
      if (file.getLen() < start) {
        return new BlockLocation[0];
  
      }
      String[] name = { "localhost:50010" };
      String[] host = { "localhost" };
      return new BlockLocation[] { new BlockLocation(name, host, 0, file.getLen()) };
    }
docs: Return an array containing hostnames, offset and size of
  portions of the given file.  For a nonexistent
  file or regions, null will be returned.
  
  This call is most helpful with DFS, where it returns
  hostnames of machines that contain the given file.
  
  The FileSystem will simply return an elt containing 'localhost'.