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

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2024-07-03 at 23:01 -0700, Christoph Hellwig wrote:
> On Wed, Jul 03, 2024 at 11:36:00AM -0400, Mike Snitzer wrote:
> > > When Mike presented LOCALIO to me at LSF, my initial suggestion
> > > was to use pNFS. I think Jeff had the same reaction.
> > 
> > No, Jeff suggested using a O_TMPFILE based thing for localio
> > handshake.  But he had the benefit of knowing NFSv3 important for the
> > intended localio usecase, so I'm not aware of him having pNFS design
> > ideas.
> 
> How does O_TMPFILE fit in here?  NFS doesn't even support O_TMPFILE.
> 

At LSF we were tossing around ideas about how to detect whether the
client and server were on the same host. My thinking was to have a
common fs (maybe even a tmpfs) that was exported by all of the servers
on the host and accessible by all of the containers on the host.

The client would then do an O_TMPFILE open in that tmpfs, write some
data to it (uuids or something) and determine the filehandle. Then it
could issue a v3 READ against the NFS server for that filehandle and if
it worked and the contents were as expected you could be sure you're on
the same host. The client could then just close the file and it would
be cleaned up.

The problem of course is that that requires having a fs that is
commonly accessible between all of the containers, which is a bit more
setup than is ideal.

The localio protocol (particularly with Neil's suggested improvements)
is really a better scheme I think.
-- 
Jeff Layton <jlayton@kernel.org>