  if (ch.status == CH_NOT_APPLIED)
    {
      ch.old_mode = file_stats->st_mode;
      ch.new_mode = mode_adjust (ch.old_mode, S_ISDIR (ch.old_mode) != 0,
                                 umask_value, change, nullptr);
      bool follow_symlink = !!dereference;
      if (dereference == -1) /* -H with/without -R, -P without -R.  */
        follow_symlink = ent->fts_level == 0;
      if (fchmodat (fts->fts_cwd_fd, file, ch.new_mode,
                    follow_symlink ? 0 : AT_SYMLINK_NOFOLLOW) == 0)
        ch.status = CH_SUCCEEDED;
      else
        {
          if (! is_ENOTSUP (errno))
            {
              if (! force_silent)
                error (0, errno, _("changing permissions of %s"),
                       quoteaf (file_full_name));

              ch.status = CH_FAILED;
            }
          /* else treat not supported as not applied.  */
        }
    }
…
  if (CH_NO_CHANGE_REQUESTED <= ch.status && diagnose_surprises)
    {
      mode_t naively_expected_mode =
        mode_adjust (ch.old_mode, S_ISDIR (ch.old_mode) != 0,
                     0, change, nullptr);
      if (ch.new_mode & ~naively_expected_mode)
        {
          char new_perms[12];
          char naively_expected_perms[12];
          strmode (ch.new_mode, new_perms);
          strmode (naively_expected_mode, naively_expected_perms);
          new_perms[10] = naively_expected_perms[10] = '\0';
          error (0, 0,
                 _("%s: new permissions are %s, not %s"),
                 quotef (file_full_name),
                 new_perms + 1, naively_expected_perms + 1);
          ch.status = CH_FAILED;
        }
    }

Warm-up