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Date:   Tue, 27 Oct 2020 13:25:45 -0400
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Leon Romanovsky <leon@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-rdma@vger.kernel.org
Subject: Re: [PATCH 00/20] NFSD support for multiple RPC/RDMA chunks
Message-ID: <20201027172545.GB1644@fieldses.org>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Tue, Oct 27, 2020 at 09:24:54AM -0400, Chuck Lever wrote:
> Hi Leon-
> 
> > On Oct 27, 2020, at 2:08 AM, Leon Romanovsky <leon@kernel.org> wrote:
> > 
> > On Mon, Oct 26, 2020 at 02:53:53PM -0400, Chuck Lever wrote:
> >> This series implements support for multiple RPC/RDMA chunks per RPC
> >> transaction. This is one of the few remaining generalities that the
> >> Linux NFS/RDMA server implementation lacks.
> >> 
> >> There is currently one known NFS/RDMA client implementation that can
> >> send multiple chunks per RPC, and that is Solaris. Multiple chunks
> >> are rare enough that the Linux NFS/RDMA implementation has been
> >> successful without this support for many years.
> > 
> > So why do we need it? Solaris is dead, and like you wrote Linux systems
> > work without this feature just fine, what are the benefits? Who will use it?
> 
> The Linux NFS implementation is living. We can add the ability
> to provision multiple chunks per RPC to the Linux NFS client at
> any time.
> 
> Likewise any actively developed NFS/RDMA implementation can add
> this feature. The RPC/RDMA version 1 protocol does not have the
> ability to communicate the maximum number of chunks the server
> will accept per RPC.
> 
> Other server implementations do support multiple chunks per RPC.
> The Linux NFS/RDMA server implementation has always been incomplete
> in this regard.

Can the client can detect the server's lack of support and fall back, or
does the server's incompleteness violate the RFC in some way that can
actually cause a failure to interoperate?

--b.

> And the Linux NFS server implementation (the non-transport specific
> part) already supports multiple data payloads per NFSv4 COMPOUND.
> 
> 
> Restoring a little more of the cover letter:
> 
> >> Along with multiple chunk support, this series adds the following
> >> benefits:
> >> 
> >> - More robust input sanitization of RPC/RDMA headers
> >> - An internal representation of chunks that is agnostic to their
> >>  wire format
> 
> The Linux NFS/RDMA server implementation does need to have better
> input sanitization.
> 
> And there is a version 2 of RPC/RDMA under active development:
> 
> https://datatracker.ietf.org/doc/draft-ietf-nfsv4-rpcrdma-version-two/
> 
> Having some protocol version agnosticism in our transport might
> be necessary eventually.
> 
> --
> Chuck Lever
> 
>