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

[Tom Talpey <[e-mail]>]

On 5/8/2017 3:10 PM, Chuck Lever wrote:
>
>> On May 8, 2017, at 2:53 PM, Tom Talpey <[e-mail]> wrote:
>>
>> On 5/8/2017 1:34 PM, Chuck Lever wrote:
>>>
>>>> On May 8, 2017, at 9:58 AM, Chuck Lever <[e-mail]> wrote:
>>>>
>>>>>
>>>>> On May 8, 2017, at 8:35 AM, Tom Talpey <[e-mail]> wrote:
>>>>>
>>>>> On 5/4/2017 11:00 AM, Chuck Lever wrote:
>>>>>> I've tried to address your concerns, and I changed the segment count
>>>>>> limit to document what we know about the current Solaris implementations.
>>>>>> I liked the "be conservative in what you send" idea, but I couldn't find
>>>>>> a way to work it in that was not awkward.
>>>>>>
>>>>>> If this text is OK, I'll submit a fresh I-D revision after WGLC ends on
>>>>>> Friday.
>>>>>
>>>>> Well that wasn't enough time for me to respond since I was traveling
>>>>> from SambaXP in Germany, but the text does look better. The statement
>>>>> below makes no requirement on the server.
>>>>>
>>>>>> 5.4.2.  Chunk List Complexity
>>>>>> ...
>>>>>> To avoid encountering server chunk list complexity limits, NFS
>>>>>> version 4 clients SHOULD follow the below prescriptions when
>>>>>> constructing transport headers:
>>>>>>
>>>>>> o  The Read list can contain either a Position-Zero Read chunk, one
>>>>>>    Read chunk with a non-zero Position, or both.
>>>>>>
>>>>>> o  The Write list can contain no more than one Write chunk.
>>>>>>
>>>>>> o  Any chunk can contain up to sixteen RDMA segments.
>>>>>
>>>>> I would suggest the following modifications to the above.
>>>>>
>>>>> "In accordance with chunk list processing limits of existing
>>>>> server implementations, NFS Version 4 clients SHOULD maximally
>>>>> follow the below prescriptions when constructing requests to
>>>>> be transported by RPC-over-RDMA. Additionally, NFS Version 4
>>>>> servers SHOULD minimally be prepared to accept and process such
>>>>> requests."
>>>>
>>>> Actually I think "servers MUST be prepared" is appropriate here,
>>>> although IMO "clients should follow the below" implies the server
>>>> side requirements already. But no harm in making it explicit.
>>>>
>>>>
>>>>>> NFS version 4 clients wishing to send more complex chunk lists can
>>>>>> provide configuration interfaces to bound the complexity of NFS
>>>>>> version 4 COMPOUNDs, limit the number of elements in scatter-gather
>>>>>> operations, and avoid other sources of RPC-over-RDMA chunk overruns
>>>>>> at the receiving peer.
>>>>>>
>>>>>> An NFS Version 4 server has some flexibility in how it indicates that
>>>>>> an RPC-over-RDMA Version One message received from an NFS Version 4
>>>>>> client is valid but cannot be processed.  Examples include:
>>>>>
>>>>>
>>>>> Strongly suggest deleting the words "has some flexibility" and "Examples
>>>>> include". We've already had this discussion, so I will just suggest the
>>>>> following.
>>>>>
>>>>> "An NFS Version 4 server SHOULD return one of the following responses
>>>>> to a client which has sent a request containing RPC-over-RDMA chunks
>>>>> which cannot be processed due to exceeding server implementation
>>>>> limits"
>>>>
>>>> Both look fine to me. Spencer, if you're willing, I can replace -10
>>>> with a revision that includes these changes.
>>>
>>> Here's the new text. I'll wait for Tom to respond before cutting -11.
>>>
>>>
>>> 5.4.2.  Chunk List Complexity
>>>
>>>   The RPC-over-RDMA Version One protocol does not place any limit on
>>>   the number of chunks or segments that may appear in Read or Write
>>>   lists.  However, for various reasons NFS version 4 server
>>>   implementations often have practical limits on the number of chunks
>>>   or segments they are prepared to process in a single RPC transaction
>>>   conveyed via RPC-over-RDMA Version One.
>>>
>>>   These implementation limits are especially important when Kerberos
>>>   integrity or privacy is in use [RFC7861].  GSS services increase the
>>>   size of credential material in RPC headers, potentially requiring
>>>   more frequent use of Long messages.  This can increase the complexity
>>>   of chunk lists independent of the NFS version 4 COMPOUND being
>>>   conveyed.
>>>
>>>   In accordance with chunk list processing limits of existing server
>>>   implementations, NFS Version 4 clients SHOULD follow the
>>>   prescriptions listed below when constructing RPC-over-RDMA Version
>>>   One messages.  NFS Version 4 servers MUST be prepared to accept and
>>>   process such requests.
>>
>> My only comment is on the above paragraph, on which I had suggested
>> adding "maximally" and "minimally" in an attempt to convey that these
>> were not absolute requirements, i.e. no more, no less than the listed
>> values. That's not the intent, right?
>
> The server is required to accept the listed bullets at a minimum,
> and the client should not send more than the list bullets, but
> it can send more if it is confident the server supports it. And,
> the stated limits are based on existing implementations, not on
> any particular limit in the transport protocol.
>
> I think we agree on the intent.
>
>
>> Again, my suggestion is to state these as "safe" values, to be used by
>> the client when no other knowledge of the actual limits exists.
>
> I had some trouble with "safe" because it's kind of an undefined
> term in this context. My preference is the paragraph should state
> what it means directly.
>
> It still feels to me like "SHOULD follow" means it is OK for the
> client to exceed the stated limits. So the current text says the
> same thing with and without "maximally" or "minimally" and already
> conveys the above intent.
>
>
>> The server text is ok.
>>
>> Along those lines then, how about:
>>
>>  "In accordance with chunk list processing limits of existing server
>>   implementations, in the absence of explicit knowedge of the server's
>>   limits, NFS Version 4 clients SHOULD follow the prescriptions listed
>>   below when constructing RPC-over-RDMA Version One messages.  All NFS
>>   Version 4 servers MUST be prepared to accept and process such
>>   requests."
>
> My counter-offer ;-)
>
>    In the absence of explicit knowledge of the server’s limits, NFS
>    Version 4 clients SHOULD follow the prescriptions listed below when
>    constructing RPC-over-RDMA Version One messages.  NFS Version 4
>    servers MUST accept and process such requests.

We do agree on the intent, and this text is fine. I wasn't trying to
wordsmith; this text removes the previous ambiguity.

Tom.