Re: State of NFSv4 VolatileFilehandles

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Aug 04, 2011 at 01:21:32PM -0400, Trond Myklebust wrote:
> On Thu, 2011-08-04 at 13:03 -0400, J. Bruce Fields wrote: 
> > On Thu, Aug 04, 2011 at 09:48:32AM -0700, Myklebust, Trond wrote:
> > > > -----Original Message-----
> > > > From: J. Bruce Fields [mailto:bfields@fieldses.org]
> > > > Oh, neat, I'd forgotten that; you're thinking of STATUS4_FIXED?  But
> > > > I'm
> > > > not sure it does the job:
> > > > 
> > > > 	STATUS4_FIXED, which indicates a read-only image in the sense
> > > > 	that it will never change.  The possibility is allowed that, as
> > > > 	a result of migration or switch to a different image, changed
> > > > 	data can be accessed, but within the confines of this instance,
> > > > 	no change is allowed.  The client can use this fact to cache
> > > > 	aggressively.
> > > > 
> > > > OK, so permission to set your attribute cache timeout very high,
> > > > perhaps, but I don't see why "changed data" couldn't mean changed
> > > > paths....
> > > 
> > > No, but you can presumably use the FSLI4BX_CLSIMUL flag from
> > > fs_locations_info in order to find an equivalent replica.
> > 
> > I lost you.
> > 
> > Actually my real problem is that I don't understand the description of
> > STATUS4_FIXED.  What does "or switch to a different image" mean?  Not
> > "migration", or the sentence would have ended before the "or".
> > 
> > I read it as allowing a server admin to replace the filesystem image in
> > place, in which case from the client's point of view this allows the
> > filesystem to change at any time.  Which makes the whole thing not
> > terribly useful, except (as the last sentence says) as a caching hint.
> 
> If the server admin replaces one filesystem, with a different
> filesystem, then nothing is going to work anyway. I don't see how that
> is relevant. That's a case of 'doctor it hurts...'
> 
> The bit that _is_ relevant is the 'migration' part, but since the
> fs_locations_info FSLI4BX_CLSIMUL flag allows you to conclude that
> replica is an exact replica at all times (i.e. contents are guaranteed
> to be the same even if filehandles, directory cookies, etc are not) then
> the STATUS4_FIXED flag does allow you to assume that paths have not
> changed.

So you're position is that "or switch to a different image" in the above
is redundant, or just a mistake?

--b.