code: private FileSystem getSrcFileSystem(Path src, boolean verifyChecksum
        ) throws IOException { 
      FileSystem srcFs = src.getFileSystem(getConf());
      srcFs.setVerifyChecksum(verifyChecksum);
      return srcFs;
    }
docs: Return the {@link FileSystem} specified by src and the conf.
  It the {@link FileSystem} supports checksum, set verifyChecksum.