Re: [nfsv4] Review of draft-ietf-nfsv4-rfc5667bis-09

[Tom Talpey <[e-mail]>]

On 4/19/2017 11:14 AM, Chuck Lever wrote:
> Hi Tom-
>
>> On Apr 18, 2017, at 11:08 PM, Tom Talpey <[e-mail]> wrote:
>>
>> I noticed the same thing, and I'll add that the MUST reject condition
>> is very confusing because it allows an "or". In my opinion a MUST is
>> always a single requirement, never ambiguous.
>
> I agree this kind of thing is tricky. I wrote it as "the server MUST
> reject the RPC". That's the single requirement. The choice is how the
> rejection is conveyed to the client.

The statement "MUST reject" is not testable. So, while it may be
understood what is intended, there is nothing implementable in the
MUST. The "or" is a similar situation, it prescribes a choice, which
does not define a protocol.

>> Is there some reason you want to allow such a choice? I think you'll
>> find that, worded properly, it becomes actually much less implementable
>> and interoperable than you may think.
>
> The Solaris server can return an RPC-level error in cases like this.

Well, this is happening because the Solaris server is (probably) just
handing the chunk list up to the RPC layer, and it's the RPC (XDR)
processing that detects any problem.

On the other hand, an implementation could do the opposite, it could
process the chunks at the lower layer, before ever invoking RPC
processing. This would naturally lead to a non-RPC error.

The challenge in defining the protocol is to hide these possibilities.

> I think there are similar choices allowed in rfc5666bis. Let's say
> that in a perfect world, I would go with only ERR_CHUNK, but I'm
> documenting existing implementation behavior here.
>
> I'm not sure it matters to the client: both errors are permanent and
> the RPC is terminated on the client.
>
> I'm open to alternatives.

The icky way to do this is to split into two weak requirements.

    If an NFS version 4 client sends an RPC Call with a Read list that
    contains more chunks than an NFS version 4 server is prepared to
    process, the server SHOULD reject the request by responding with an
    RDMA_ERROR message with the rdma_err value set to ERR_CHUNK. The
    server MAY reject the RPC with an RDMA_MSG message containing an RPC
    Reply with an accept status of GARBAGE_ARGS.

This at least makes it clear which response is "preferred". And one
would hope a future draft would decide.

I have a second question though. How does the client determine what is
the actual error? As in, how many chunks were allowed? Does the upper
layer have to recover, and if so what are the implications?

Yes, I know 5667 did not explore this very well. Mea culpa.


Tom.



>> On 4/18/2017 6:32 PM, karen deitke wrote:
>>> Hi Chuck, its unclear what you mean by "is prepared to process" in the text below.
>>> Other than that, looks good.
>>>
>>> Karen
>>>
>>> 5.4.1
>>>   If an NFS version 4 client sends an RPC Call with a Write list that
>>>   contains more chunks than an NFS version 4 server is prepared to
>>>   process, the server MUST reject the RPC by responding with an
>>>   RDMA_ERROR message with the rdma_err value set to ERR_CHUNK.
>>>
>>>
>>>   If an NFS version 4 client sends an RPC Call with a Read list that
>>>   contains more chunks than an NFS version 4 server is prepared to
>>>   process, the server MUST reject the RPC by responding with an
>>>   RDMA_MSG message containing an RPC Reply with an accept status of
>>>   GARBAGE_ARGS, or with an RDMA_ERROR message with the rdma_err value
>>>   set to ERR_CHUNK.
>>>
>>>
>>> On 4/18/2017 1:21 PM, David Noveck wrote:
>>>> *Overall Evaluation*
>>>> *
>>>> *
>>>> Major improvement over RFC5667.  Almost ready to ship.  No technical
>>>> issues.
>>>>
>>>> A lot of my comments are basically editorial and are offered on a
>>>> take-it-or-lease-it basis.
>>>>
>>>> I think some clarification in Section 5.4.1 is needed although not
>>>> necessarily in the ways suggested below,
>>>>
>>>> *Comments by Section*
>>>> *5.4.1. Multiple DDP-eligible Data Items*
>>>> Giventhat READ_PLUS no longer has any DDP-eligible data items, the
>>>> situation described in the fifth bullet can no longer arise. I suggest
>>>> deleting the bullet.
>>>> The penultimate paragraph can be read as applying to some situations
>>>> in which it shouldn't and where the extra chunks would very naturally
>>>> ignored. For example, if you had on write chunk together with a READ
>>>> operation which failed, the server would have more chunks (i.e. one)
>>>> than the number it is prepared to process (i.e. zero). Suggest, as a
>>>> possible replacement:
>>>>
>>>>    Normally, when an NFS version 4 client sends an RPC Call with a
>>>>    Write list that contains multiple chunks. each such, when matched
>>>>    with a DDP-eligible data item in the response, directs the
>>>>    placement of the data item as specified by
>>>>    [I.D.-nfsv4-rfc5666bis]. When there are DDP-eligible data items
>>>>    matched to write chunks that an NFS version 4 server is not
>>>>    prepared to process, the server MUST reject the RPC by responding
>>>>    with an RDMA_ERROR message with the rdma_err value set to ERR_CHUNK.
>>>>
>>>> With regard to the last paragraph, I am curious that this paragraph,
>>>> unlike the previous one, allows GARBGEARGS. Is this so because that
>>>> would be allowed if the chunks in question had offsets other than
>>>> those that correspond to DDP-eligible data items? If so, please
>>>> consider the following possible replacement.
>>>>
>>>>    Normally, when an NFS version 4 client sends an RPC Call with a
>>>>    Read list that contains multiple chunks, each such, when properly
>>>>    matched with a DDP-eliigible data item in the request, directs the
>>>>    fetching of the the data item as specified by
>>>>    [I.D.-nfsv4-rfc5666bis]. When there are DDP-eligible data items
>>>>    matched to read chunks that an NFS version 4 server is not
>>>>    prepared to process, the server MUST reject the RPC by responding
>>>>    with an RDMA_ERROR message with the rdma_err value set to ERR_CHUNK.
>>>>
>>>> *5.6. Session-Related Considerations*
>>>> In the third sentence of the second paragraph, suggest replacing "no
>>>> different" by "not different".
>>>> In the last sentence of the last paragraph, suggest replacing "is not"
>>>> by "were not"
>>>>
>>>>
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> --
> Chuck Lever
>
>
>
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