Re: [PATCH v11 00/20] nfs/nfsd: add support for localio

NeilBrown
2024-07-06T06:37:31Z

On Sat, 06 Jul 2024, Christoph Hellwig wrote:
> On Sat, Jul 06, 2024 at 08:08:07AM +1000, NeilBrown wrote:
> > I would like to see a good explanation for why NOT NFSv3.
> > I don't think NFSv3 is obsolete. The first dictionary is "No longer in
> > use." which certainly doesn't apply.
> > I think "deprecated" is a more relevant term. I believe that NFSv2 has
> > been deprecated. I believe that NFSv4.0 should be deprecated. But I
> > don't see any reason to consider NFSv3 to be deprecated.
>
> The obvious answer is that NFSv4.1/2 (which is really the same thing)
> is the only version of NFS under development and open for new features
> at the protocol level. So from the standardization perspective NFSv3
> is obsolete.

RFC-1813 is certainly obsolete from a standardization perspective - it
isn't even an IETF standard - only informational. It can't be extended
with any hope of interoperability between implementations.

But we don't want interoperability between implementations. We want to
enhance the internal workings of one particular implementation. I don't
see that the standards status affects that choice.

>
> But the more important point is that NFSv4 has a built-in way to bypass
> the server for I/O namely pNFS. And bypassing the server by directly
> going to a local file system is the text book example for what pNFS
> does. So we'll need a really good argument why we need to reinvented
> a different scheme for bypassing the server for I/O. Maybe there is
> a really good killer argument for doing that, but it needs to be clearly
> stated and defended instead of assumed.

Could you provide a reference to the text book - or RFC - that describes
a pNFS DS protocol that completely bypasses the network, allowing the
client and MDS to determine if they are the same host and to potentially
do zero-copy IO.

If not, I will find it hard to understand your claim that it is "the
text book example".

Also, neither you nor I are in a position to assert what is needed for a
change to get accepted. That is up the the people with M: in front of
their email address. I believe that any council that either of us give
will considered with genuine interest, but making demands seems out of
place.

Thanks,
NeilBrown