Re: [storm] iSER - one last issue

[Michael Ko <[e-mail]>]

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
To: Tom Talpey ; [e-mail] ; [e-mail] ; 
[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]]
Sent: Thursday, January 19, 2012 8:09 AM
To: Hemal Shah; [e-mail]; [e-mail]; 
[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]]
Sent: Thursday, January 19, 2012 10:38 AM
To: Tom Talpey; [e-mail]; [e-mail]; 
[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]]
Sent: Thursday, January 19, 2012 5:51 AM
To: Hemal Shah; [e-mail]; [e-mail]; 
[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]] On Behalf Of 
Hemal Shah
Sent: Wednesday, January 18, 2012 6:56 PM
To: [e-mail]; [e-mail]; [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]] On Behalf Of 
[e-mail]
Sent: Wednesday, January 18, 2012 3:10 PM
To: [e-mail]; [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]]
Sent: Wednesday, January 18, 2012 2:22 PM
To: Black, David; [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]

To: [e-mail] ; [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