> I'm not really sure what from-below VOPs make sense. :-)

Well ... I think it's fairly obvious that most people can live without any
of the functionality I'm suggesting :^) it just seems to me that it could
be useful in some cases.

How about remove/rmdir, as they affect the file metadata (the implicit bit
"file exists in the fs namespace"). This really isn't a very important
problem, but can cause user confusion if it is visible to them (PR #4315).

If the upper layer is caching other metadata --- say it provides ACLs or
some other permission-modifying service sufficiently more complex than
UMAPFS that it has to store modifiable data somewhere --- then it might
want to know if the underlying file's permissions have been modified; so
add setattr to the list.

If the upper layer is caching file data --- say an encryption layer --- it
would be unfortunate if the lower vnode were truncated, and the upper
layer didn't notice and wrote the cached data.  Not necessarily an error,
but an unnecessary and undesirable artifact.  So truncate, too.

Finally, you might want a general purpose file watcher for a small number
of files, and be unwilling to put a stacked filesystem over their
containing directories...NT's file event auditing comes to mind.  For this
you'd need to be passed every operation that someone might want to audit,
which would probably include everything except VOP_PRINT.

Again not functionality that most people want/need, nor certainly anything
that is necessary for the stacked filesystems we currently have.  But
possibly useful.

------------------------------------------------------------------------
Konrad Schroder          http://www.hitl.washington.edu/people/perseant/
System Administrator                        perseant@hitl.washington.edu
Human Interface Technology Lab                    Voice: +1.206.616.1478
Box 352142, University of Washington, 98195, USA    FAX: +1.206.543.5380