Re: State of NFSv4 VolatileFilehandles

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

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.

--b.