> Has anyone implemented a filesystem with copy-on-write semantics?  I'd like
> to be able to, for instance, have a file which will be a link to another file,
> until it gets written to, at which point, it becomes a new file, containing
> whatever new data.  Is this monumentally stupid for a reason which will
> become apparent before this message makes it back to me, and/or is it
> implemented already?

If I understand you correctly, most of what you intend can be had with
mount_union(8).

Hope it helps.
--
ws@TooLs.DE     (Wolfgang Solfrank, TooLs GmbH) 	+49-228-985800