Re: [RFC] Reinstate NFS exportability for JFFS2.

[David Woodhouse <dwmw2@infradead.org>]

On Sat, 2008-08-02 at 17:33 -0400, J. Bruce Fields wrote:
> On Sat, Aug 02, 2008 at 09:42:32PM +0100, David Woodhouse wrote:
> > On Sat, 2008-08-02 at 14:26 -0400, J. Bruce Fields wrote:
> > > Could you add a readdirplus vfs operation which took a flag indicating
> > > how much extra information you're going to need?
> > 
> > Actually, if we're screwing with readdir then xfs would like to know how
> > much it's going to be asked to read, rather than just have the filldir
> > callback return zero when it's done.
> 
> OK.
> 
> > > The three cases where readdir can be called are:
> > >         - ordinary readdir, for which the existing filldir_t provides
> > >           all the information needed.
> > >         - nfsv3 readdirplus, where the only additional information
> > >           needed is whether there's a mountpoint.
> > 
> > It also wants a file handle.
> 
> Oops, right.
> 
> > For which I think it just needs
> > i_generation in addition to the information it already has.
> 
> Typically, right, though the filesystem's allowed some choice about what
> exactly it wants to use in the filehandle.  I don't know how the various
> filesystems are actually using that in practice.

That's OK. If we do ->lookup_fh() and they're making their own, they can
put what they like in it.

> > >         - nfsv4 readdir, where we may need all the stat info, acls,
> > >           etc., etc.
> > 
> > We _might_, but most of the time we won't. It might be OK to fall back
> > to the existing double-buffer hack for the cases where we _do_ need that
> > extra information.
> 
> How bad is the "double-buffer hack" anyway?  Rather than have this as a
> fallback case that's rarely used (hence rarely tested), it might be
> simpler just to use it for everything if we're going to use it at all.

It's certainly a good enough answer for now, which is why I've posted
the patches to do exactly that.

And yes, I have wondered the same myself, since realising that we'll
need a full lookup for some NFSv4 clients anyway. Or maybe the full
->lookup_locked(), perhaps...

-- 
dwmw2