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

[Christoph Hellwig <hch@infradead.org>]

I've stated looking a bit at the code, and the architectural model
confuses me more than a bit.

A first thing that would be very helpful is an actual problem statement.
The only mention of a concrete use case is about containers, implying
that this about a client in one container/namespace with the server
or the servers in another containers/namespace.  Is that the main use
case, are there others?

I kinda deduct from that that the client and server probably do not
have the same view and access permissions to the underlying file
systems?  As this would defeat the use of NFS I suspect that is the
case, but it should probably be stated clearly somewhere.

Going from there I don't understand why we need multiple layers of
server bypass.  The normal way to do this in NFSv4 is to use pNFS
layout.

I.e. you add a pnfs localio layout that just does local reads
and writes for the I/O path.  We'd still need a way to find a good
in-kernel way to get the file structure, but compared to the two
separate layers of bypasses in the current code it should be
significantly simpler.