Re: [nfsv4] Review of draft-ietf-nfsv4-rfc5667bis-06

[Tom Talpey <[e-mail]>]

On 2/26/2017 3:29 PM, Chuck Lever wrote:
>> On Feb 25, 2017, at 3:54 PM, David Noveck <[e-mail]> wrote:
>>
>>> RFC 5667 Section 4 says:
>>
>>>> Similarly, a single RDMA Read list entry MAY be posted by the client
>>>> to supply the opaque file data for a WRITE request or the pathname
>>>> for a SYMLINK request.
>>
>> Part of the problem here is that, as you discuss later, this statement is
>> ambiguous, as the meaning of "read list entry" is not clear.
>>
>>>> The server MUST ignore any Read list for
>>>> other NFS procedures,
>>
>> As I understand it, this statement cannot apply to PZRCs, and rfc5666bis
>> has already dealt with that issue.  So, if one tried to maintain this paragraph,
>> in something like the RFC5667-form, some modification would have been
>> necessary to avoid essentially preventing any use of PZRCs
>>
>>>> as well as additional Read list entries beyond
>>>> the first in the list.
>>
>>> I take "Read list entry" to mean Read chunk, composed of
>>> multiple list entries that share the same XDR position.
>>> This comports with similar language describing Write
>>> chunks where a single list entry is indeed allowed to
>>> have multiple segments.
>>
>> Makes sense to me.
>>
>>> However, the original intent might have been "single
>>> Read segment".
>>
>> It might have been but there is no way to be sure.
>
> We can ask Tom Talpey. If he does not recall, then
> we have no way to be sure.

I agree the paragraph in question could have been more clear. I'll
hazard a guess that it should have been written as "Read list" instead
of "Read list entry", meaning, an entire scatter list is provided.
This woud certainly match the semantic for the result of an ordinary
NFS Read.

I will also observe that the statement is a MAY. That is, it prescribes
no behavior, and offers a choice to the implementer. It does not rule
out the option of posting a list.

I think you guys need to stop worrying about writing these "rules"
down so literally. The only goal of RFC5667 was to isolate the tidbits
of NFS behaviors separate from the core rpcrdma transport. The
document makes relatively few MUST requirements.

Tom.