re: open()ing a directory without O_DIRECTORY

>  - zero out on unlink() so that the data is no longer on the disk
>    (Everybody seems to have expressed preference for this solution but I
>    think this requires changing all the affected filesystems)

actually, i don't like this idea at all.  it requires additional
writes and it makes crash handling much harder later.  eg, fsdb
will have much less useful data to work from.

i really don't think it is worth making hard times harder.