Re: [storm] iSER - one last issue

[<[e-mail]>]

[WG co chair hat on]

I think the implementation aspect of this discussion is useful.

I also want to remind everyone that the following text from the storm WG charter
(http://datatracker.ietf.org/wg/storm/charter/) is highly relevant to the
message usage topic under discussion:

  Stability is critical to the usage of these protocols, so backwards
  compatibility with existing implementations will be a requirement
  imposed on for all protocol changes and additions. Note that this is a
  requirement for implementation compatibility - if it is the case that
  all implementations of a protocol have done something different than
  what the RFC specifies, it is appropriate for a new RFC to document what
  the "running code" actually does and deprecate the unused original behavior.

I think it's ok for iSER's message usage requirements to vary between iWARP
and InfiniBand - such a difference could make it more difficult to run iSER
over an RCaP gateway between iWARP and InfiniBand, but I don't think there's
much interest in doing that.  OTOH, all changes to RFC5046 need justification
under the "all implementations of a protocol have done something different
than what the RFC specifies" condition quoted above.

Thanks,
--David (as WG co-chair)

From: Tom Talpey [mailto:[e-mail]]
Sent: Thursday, January 19, 2012 3:33 PM
To: Michael Ko; Hemal Shah; Black, David; [e-mail]
Subject: RE: iSER - one last issue

More precisely, are there any iSER *initiators* that *depend* on receiving solicited events over the iWARP RDMA transport? I believe this to be a very short list, if any. But I'd be ok with being proven wrong.



From: Michael Ko [mailto:[e-mail]]
Sent: Thursday, January 19, 2012 12:39 PM
To: Hemal Shah; Tom Talpey; [e-mail]; [e-mail]
Subject: Re: iSER - one last issue

For all RCaP layers, the Send message (or any variant) MUST be used, as opposed to using RDMA Read or Write to accomplish the task.  So a SHOULD for RCaP other than iWARP is incorrect.  RFC 5040 can mandate that all RDMAP messages be supported, but it is still up to implementation to decide what messages to use in any situation.  This iSER update is meant to reflect running code and to generalize the support of iSER over any RCaP, not just iWARP.  So the question is are there any running code that uses SendSE and SendInvSE for iSER.  Conversely, if the running code can get by using Send messages to accomplish the task, what is the point of mandating a MUST at this point for SendSE and SendInvSE?  Note that the receiver cannot completely rely on the sender for the Invalidate feature anyway.  The iSER layer at the initiator is required to explicitly invalidate the STag for bidirectional commands and abnormal completion of a command.  Even when automatic invalidation is used, the iSER layer is required to sanity checking the automatic invalidation.  In other words, the iSER spec puts the burden on the receiver for doing the right thing in handling the Send messages, and not relying on the sender for the mere convenience.

Mike
----- Original Message -----
From: Hemal Shah<mailto:[e-mail]>
To: Tom Talpey<mailto:[e-mail]> ; [e-mail]<mailto:[e-mail]> ; [e-mail]<mailto:[e-mail]> ; [e-mail]<mailto:[e-mail]>
Sent: Thursday, January 19, 2012 8:44 AM
Subject: RE: iSER - one last issue

Tom,

You are welcome! You are right about 7.3.4 as the only section mandating Send message.

I think your concern about specifying the requirement for the other RCaP implementation is valid. I suggest we should word the requirements as below:

"If the RCaP layer is as specified in [RFC5040] and [RFC5041], the SendSE message MUST be used. For any other RCaP layer, the Send message SHOULD be used. "

Hemal

From: Tom Talpey [mailto:[e-mail]]<mailto:[mailto:[e-mail]]>
Sent: Thursday, January 19, 2012 8:09 AM
To: Hemal Shah; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: iSER - one last issue

Thanks for pointing out that sentence in RFC5046 7.3.4. I believe it is the only such stipulation.

I'm ok with stating the requirement as RFC5046-over-RFC5040 compliance. But this new draft opens the door to alternative behaviors, therefore it needs to be stated more clearly. What's the requirement when SendSE is not supported? And, how does the receiver know what to expect?

In other words, if it's proposed that the statement be:
                "When the RCaP layer is as specified in [RFC5040] and [RFC5041], the SendSE message MUST be used."

... then what MUST be used when the RCaP is not? That statement needs to be made, too.


From: Hemal Shah [mailto:[e-mail]]<mailto:[mailto:[e-mail]]>
Sent: Thursday, January 19, 2012 10:38 AM
To: Tom Talpey; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: iSER - one last issue

Tom,

RFC5046 is very clear about the use of Send Message Type for iSCSI control-type PDU. For specific iSCSI PDUs, Section 7 mandates the use of Send, SendSE, or SendSEInv. Section 7 of RFC5046 clearly specifies the use of specific Send Message Type for each iSCSI control-type PDUs (Login, Logout, Text request, Text response...). Section 7.3.4 mandates the use of plain-old Send also as needed. For example, see text below from 7.3.4.

For unsolicited data, if the F bit is set to 0 in a SCSI Data-out
PDU, the iSER layer at the initiator MUST use a Send Message to send
the SCSI Data-out PDU.

Regarding your comment in the second paragraph below, RFC5040 expectation is all the RDMAP messages specified in RFC5040 are supported (if that is not the case then we cannot count on any of the other RDMAP messages to be supported). So, an implementation that does not support SendSE at the sender is not compliant with RFC5040. So, your second point does not apply.

I hope that addresses your comments.

Hemal

From: Tom Talpey [mailto:[e-mail]]<mailto:[mailto:[e-mail]]>
Sent: Thursday, January 19, 2012 5:51 AM
To: Hemal Shah; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: iSER - one last issue

If using SendSE is so important here, when MUST a plain-old Send be used? There is no mention of any distinction in RFC5046 section 1.4.2 nor in this draft's section 2.4.2.

Even with a MUST on the SendSE, the behavior is indeterminate, since it would still be contingent on support for SendSE at the *sender*. This critical exception voids any normative requirement, even over iWARP. The strongest statement that can be made is SHOULD.

Tom.

From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]]<mailto:[mailto:[e-mail]]> On Behalf Of Hemal Shah
Sent: Wednesday, January 18, 2012 6:56 PM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [storm] iSER - one last issue

David and Mike,

I believe that the requirements should not be weakened and we should stick to the requirement in RFC5046.

RFC5046 required the use of specific Send Message Type for valid reasons.

In the case of requiring SendSE message use, the intent was to give a hint to the remote side to generate an event upon processing of SendSE message. For example, the SendSE is specifically carrying SCSI information that needs attention on the remote side e.g. SCSI command, Logout...

In the case of requiring SendInvSE Message, the intent was to invalidate the STag used in the data transfer as well as inform the remote side to generate an event. For example, mandating the use of SendInvSE for the SCSI response PDU for a SCSI Read limits the exposure of STag used in SCSI Read data transfer and avoids the explicit invalidation of the STag at the initiator. Plus, it allows the target to generate an event on the initiator upon the completion of SCSI Read command.

By relaxing RFC5046 requirements in the latest iSER draft, we will not only impact all iWARP based iSER implementations that rely on the use of specific Send Message Type for SCSI data transfers but also change the intended behavior of initiators and targets.

For iWARP, I strongly suggest that the iSER draft does not relax the requirements specified in RFC5046.

I hope that helps.

Hemal

From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]]<mailto:[mailto:[e-mail]]> On Behalf Of [e-mail]<mailto:[e-mail]>
Sent: Wednesday, January 18, 2012 3:10 PM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [storm] iSER - one last issue

Mike,

Thank you for the explanation, but I don't believe you've correctly stated
the intent of RFC 5046.  Here are some examples from RFC 5046's text:

1.5.  SCSI Read Overview

   The iSER Message is transferred to the target using a SendSE Message.

   The iSER layer at the target uses a SendInvSE Message to transfer the
   SCSI Response PDU back to the iSER layer at the initiator.

Similar language occurs in 1.6 SCSI Write Overview.

5.2.1.  Normal Connection Termination at the Initiator

   The iSER layer at the initiator MUST
   use a SendSE Message to send the Logout Request PDU to the target.

Similar language occurs in 5.2.2 for target side normal connection termination,
and more importantly in 7.3.1 SCSI Command:

   The iSER layer at the initiator MUST send the SCSI command in a
   SendSE Message to the target.

None of the quoted text permits use of Send instead of SendSE or SendInv
instead of SendInvSE.

What you propose to do effectively changes "MUST" to "should" (lower case,
weaker than "SHOULD"), and that sure looks like a change to RFC 5046.

Are there good implementation-based reasons to weaken these requirements now?

Does anyone else have a viewpoint on this topic?

Thanks,
--David

From: Michael Ko [mailto:[e-mail]]<mailto:[mailto:[e-mail]]>
Sent: Wednesday, January 18, 2012 2:22 PM
To: Black, David; [e-mail]<mailto:[e-mail]>
Subject: Re: iSER - one last issue

David,

Here is my rationale for using the lower case "should".

The intent of RFC5046 is that the Send Message type must be used instead of RDMA Reads or Writes.  The Solicited Event feature of the Send Message is provided as a convenience.  The receiver must still do the right thing in handling the Send Message regardless of whether the SE feature is used.  In other words, the sender is responsible for using the right format for the message (Send vs RDMA) but the receiver must not rely on the sender to determine how to handle the received message.  The same rationale goes for the Invalidate feature.

Mike
----- Original Message -----
From: [e-mail]<mailto:[e-mail]>
To: [e-mail]<mailto:[e-mail]> ; [e-mail]<mailto:[e-mail]>
Sent: Monday, January 16, 2012 2:06 PM
Subject: iSER - one last issue

Mike,

Thanks for getting the -08 version of the iSER draft posted.  I think that
draft addresses all of the open issues, but I have a question for the WG
about how to express the SendSE and SendInvSE requirements from RFC 5046.

The -08 version of the iSER draft expresses requirements for the SendSE
and SendInvSE messages (this is primarily for iSER over RDDP/iWARP) as:

The SendSE Message should be used if
supported by the RCaP layer (e.g., iWARP).

My reading of RFC 5046 is that its requirements are tighter - to accurately
reflect RFC 5046, I would replace "should" with "MUST" in the above text,
at least for iWARP.

In the alternative, if the "should"s remain, an explanatory item
needs to be added to the Appendix A list of changes from RFC 5046.

What do others think the right course of action is here, use "MUST" or
explain weakening of requirement to "should" ?

Thanks,
--David