Re: [nfsv4] Clean up for rpcrdma-version-two Read chunks

David Noveck <davenoveck@gmail.com> Tue, 05 May 2020 00:59 UTC

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From: David Noveck <davenoveck@gmail.com>
Date: Mon, 04 May 2020 20:59:29 -0400
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To: Chuck Lever <chuck.lever@oracle.com>
Cc: NFSv4 <nfsv4@ietf.org>
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Subject: Re: [nfsv4] Clean up for rpcrdma-version-two Read chunks
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On Mon, May 4, 2020, 12:13 PM Chuck Lever <chuck.lever@oracle.com> wrote:

> Two weeks ago, I presented on the status of
> draft-ietf-nfsv4-rpcrdma-version-two.
> The slides are here:
>
>
> https://datatracker.ietf.org/meeting/interim-2020-nfsv4-01/materials/slides-interim-2020-nfsv4-01-sessa-ietf-107-rpc-rdma-v2.pdf
>
> On slide 18, I described three situations involving Read chunks that do
> not appear
> to be adequately covered by RFC 8166 ("Remote Direct Memory Access
> Transport for
> Remote Procedure Call Version 1"). I'd like to propose modifications to the
> rpcrdma-version-two draft to address these cases:
>
>
> > RPC/RDMA v1 allows a position zero Read chunk to appear in an RDMA_MSG
> type Call.
> > Where does a Responder put the inline portion of such a message?
>
> I propose that in RPC/RDMA version 2, a Responder MUST return
> RDMA2_ERR_BAD_XDR if
> a Requester sends a Read list containing a position zero Read chunk as
> part of
> header type other than RDMA2_NOMSG.
>

Agree.


>
> > RPC/RDMA v1 does not explicitly require an RDMA_NOMSG type Call to have
> a position
> > zero Read chunk. Does such a message have gaps? Are they zero-filled?
>
>
> I propose that in RPC/RDMA version 2, a Responder MUST return
> RDMA2_ERR_BAD_XDR if
> a Requester sends an RDMA2_NOMSG header type whose Read list does not
> include a
> position zero Read chunk.
>

As stated, this would forbid NOMSG bring used to send a long reply.  I
think the text to address this needs to be careful not to foreclose that.
Your text above uses the word "requester" assuming this is sufficient but
the only way a peer receiving message could determine whether it was sent
by a requester or responder is my looking at the message, which,in this
case, does not exist.

>
>
> > RPC/RDMA v1 does not prevent or prohibit overlapping Read chunks. Is the
> correct
> > response ERR_CHUNK?
>
> A protocol change would be needed to totally prevent the expression of
> overlapping
> Read chunks. Maybe it's a little too late to address that in RPC/RDMA
> version 2.
>

I think you mean version 1.  Nobody seems up to do rfc8166bis.

>
> I propose that in RPC/RDMA version 2, a Responder MUST return
> RDMA2_ERR_BAD_XDR if
> a Requester sends a Read list with chunks whose offsets and lengths result
> in the
> same message byte position appearing in more than one Read chunk.
>

This would require sorting by the receiver. It might be better to place
responsibility on the sender to sort these.


> Comments/concerns?
>
> --
> Chuck Lever
>
>
>
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