unix domain sockets on nullfs(5)

[Kostik Belousov]

On Thu, Jan 12, 2012 at 11:17:26PM +0200, Mikolaj Golub wrote:
> On Tue, Jan 10, 2012 at 10:30 PM, Mikolaj Golub <trociny at freebsd.org> wrote:
> >
> > On Tue, 10 Jan 2012 14:02:34 +0000 Robert N. M. Watson wrote:
> >
> >  RNMW> (1) I don't think the new behaviour should be optional -- it was always
> >  RNMW> the intent that nullfs pass through all behaviours to the underlying
> >  RNMW> layer, it's just that certain edge cases didn't appear in the original
> >  RNMW> implementation. Memory mapping was fixed a few years ago using similar
> >  RNMW> techniques. This will significantly reduce the complexity of your
> >  RNMW> patch, and also avoid user confusion since it will now behave "as
> >  RNMW> expected". Certainly, mention in future release notes would be
> >  RNMW> appropriate, however.
> >
> > I don't mind having only the new behavior, as I can't imagine where I would
> > need a nullfs with nosobypass option mounted and I also like when things are
> > simple :-).
> >
> > On the other hand there might be people who relied on the old behavior and who
> > would be surprised if it had changed.
> >
> > So, if other people agree I will remove the old behaviour to make the patch
> > simpler. Another option would be to have sobypass by default with possibility
> > to (re)mount fs with nosobypass.
> >
> 
> If we agree to have only the new behavior then nullfs won't need modification
> at all, it will work as expected automatically. The patch could be (with updated
> locking for the connect case):
> 
> http://people.freebsd.org/~trociny/VOP_UNP.1.patch

I suggest to split the exclusive->shared locking change into separate patch,
to be committed either before or after the VOP_UNP (better to do it
before to not change the interface of VOP).

You do not need local variable vp in the default implementations of
vops at all, use ap->a_vp directly.
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