sub fileop($;$) {
    my ($op, @argv)=@{my $_=shift};
    use Carp qw(cluck);
    no strict 'refs';
    &{"CORE::".$op}(@argv) || do {
      cluck (P "ERROR: $! doing %s(%s): (%s)%s", $op, (join ', ', @argv), $!,
        @_?" (extra info: ".$_[0].")":"");
      exit (0+$!)
    }
  }
# can call this with:
    fileop(['rename', $from_name, $tmpnam]);
    fileop(['link', $name_of_to_node, $from_name]);