Re: [nfsv4] draft-ietf-nfsv4-rpcrdma-bidirection-03 review

[Chuck Lever <[e-mail]>]

> On May 27, 2016, at 8:24 AM, David Noveck <[e-mail]> wrote:
> 
> I wrote:
> > but I have a problem with writing the spec as if 
> > such situations don't exist.
> 
> I've been thinking more about this.  I think the problem lies in what I mean by 
> "the spec".  If that means "rfc566bis", then such situations cannot exist.
> rfc566bis seems to only deal with forward direction operation.  In such an environment, 
> if you are a client and you receive a message, it has to be a reply.  Similarly, if you are 
> server and you receive a message, it has to be a request.  So there is no occasion for the
> kind of ambiguity I'm concerned about.
> 
> On the other hand, if "the spec" means "the specification of RPC-over-RDMA Version One",
> in which multiple directions of operation can be supported, the ambiguity is unavoidable. If 
> you (client or server) receive a message you do not know a priori, whether it is a request or 
> a reply and there are situations in which the receiver cannot determine, given a malformed 
> message, whether it has received a malformed request or reply.

I left the existing language in rpcrdma-bidirection.
So Section 4.1 still has:

>    When message direction is not fully determined by context or by an
>    accompanying RPC message with a call direction field, it is not
>    possible to tell whether the header credit value is a request or
>    grant, or whether the value applies to the forward direction or
>    backward direction.  In such cases, the receiver MUST NOT use the
>    header’s credit value.


Adding the "RDMA_ERROR is responder-to-requester only"
to rfc5666bis, plus this from Section 5.1:

>    The rdma_vers field MUST contain the same value in backward and
>    forward direction Call messages on the same connection.


And this from Section 6:

>    Therefore, an Upper Layer Protocol consumer MUST NOT perform backward
>    direction ONC RPC operations unless the peer consumer has indicated
>    it is prepared to handle them.


All serve to close the largest windows of ambiguity we
know about. But true enough, there may be others.


--
Chuck Lever