Proposal to augment MPA connection set up frame

I have a comment on MPA draft.
It now defines very nicely an
Initiator/Responder sequence.
But it looks deficient for a broad set of ULPs.
Most of the client-server ULP uses two type
of Responses: "accept" and "reject".
The MPA draft does not provide a way
to differentiate between these 2 responses.

Here is one example of an application use.
One of the common way the private data is used
is to negotiate RDMA Read credits for
a connection to be used by RDDP.
An Initiator passes in private data
a requested RDMA credits.
Responder either accepts a connection or
rejects a request specifying how many
RDMA Read credits it can support.

Currently the Responder has 2 legal choices.
One it can terminate a connection.
This does not convey any information to
the Initiator.

The second choice is to generate Responder
Frame even though RDMA Read credits
requested can not be satisfied.
This will establish connection but it can not
be used as intended by the Initiator.
Initiator can either tear down the established
stream mode connection or use connection
with Responder RDMA credits supported.
This is de-facto ULP protocol since Responder
Frame will include the RDMA Read credits
it can support. On top of that both sides
have to agree on the action they will take.

While ULP can use a protocol over private data
to differentiate between accept and reject,
given a commonality of this semantic for ULPs
we can use one bit from the Reserved area of
MPA frame for the Responder frame to differentiate
between accept and reject responses.

Proposal:
for Responder MPA frame the 1st Reserved bit
to be used as accept/reject bit. 0 for accept,
1 for reject.
The bit will be called Type (T) in figure 7.


Arkady Kanevsky                                email: [email protected]
Network Appliance                              phone: 781-768-5395
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