docs: def unpacktar(tarfile, destdir):
      """ Unpack given tarball into the specified dir """
      nullfd = open(os.devnull, "w")
      tarfile = cygpath(os.path.abspath(tarfile))
      log.debug("unpack tar %s into %s", tarfile, destdir)
      try:
          check_call([TAR, '-xzf', tarfile], cwd=destdir,
                     stdout=nullfd, preexec_fn=_noumask)
      except Exception:
          log.exception("Error unpacking tar file %s to %s", tarfile, destdir)
          raise
      nullfd.close()