Re: [storm] iSER - one last issue: update

[Mallikarjun Chadalapaka <[e-mail]>]

I think we should go with [1] and [2a] that David outlined.  As Hemal said,
there were good reasons why RFC 5046 stipulated SendInvSE and SendSE, where
it did.  I would rather not weaken it, at least for the iWARP RCaP
ecosystem.

 

Mallikarjun

 

 

From: [e-mail] [mailto:[e-mail]] On Behalf Of
Tom Talpey
Sent: Tuesday, January 24, 2012 5:49 AM
To: [e-mail]; [e-mail]
Subject: Re: [storm] iSER - one last issue: update

 

[WG co-chair hat off]

 

> [2a] Leave things alone - if the RCaP supports Solicited Events, then the
"MUST"

> requirements for SendSE and SendInvSE apply as they did in RFC 5046.

 

The core issue here is the statement "if the RCaP supports Solicited
Events". Both the iWARP and Infiniband protocols support them. But
Infiniband does not require all adapters support them - the architecture
requires it for HCAs but leaves it optional for TCAs (Infiniband
architecture v1.2.1 table 319 on page 1045). Because this latter property
cannot be detected by the remote upper layer, it does not appear to be
possible to make an interoperable decision for all protocols and all
implementations.

 

That said, in the absence of any existing iSER-over-iWARP SendSE
implementations, I agree the entire discussion is effectively moot.

 

Tom.

 

From: [e-mail] [mailto:[e-mail]] On Behalf Of
[e-mail]
Sent: Monday, January 23, 2012 8:05 PM
To: [e-mail]
Subject: [storm] iSER - one last issue: update

 

[WG chair hat off]

 

This is a message intended for discussion and comments.

 

Looking for a way forward, this observation from Mike seems like a useful
place to start:

 

> This iSER update is meant to reflect running code and to generalize the
support of iSER over any RCaP, not just iWARP. 

 

RFC 5046 (iSER) was written on the assumption that the RCaP layer supports
Solicited

Event functionality.  I also read RFC 5040 as requiring RDMAP
implementations (part of

iWARP) to support Solicited Event functionality.

 

This first step seems easy:

 

[1] There are RCaPs that don't support Solicited Event functionality; those
RCaPs have

no choice - they MUST use Send (not SendSE) and SendInv (not SendInvSE).  

 


I would prefer to write iSER requirements in terms of whether the RCaP
supports

Solicited Event functionality as opposed to calling out iWARP explicitly as
having

different requirements.  OTOH, I'm prepared to listen to arguments to the
contrary.

 

Beyond that, I think there are two primary choices:

 

[2a] Leave things alone - if the RCaP supports Solicited Events, then the
"MUST"

requirements for SendSE and SendInvSE apply as they did in RFC 5046.

 

[2b] In the alternative, if there are iSER implementations for iWARP that
aren't using

SendSE and SendInvSE in accordance with RFC 5046's requirements, then we
need to change

those requirements to match the implementations.

 

I would hope we can agree on [1], and I believe that'll cover the InfiniBand
case, right?

 

For choosing between [2a] and [2b] it would help a lot to konw what iSER
over iWARP

implementations are actually doing (SendSE/SendInvSE vs. Send/SendInv).

 

*** Who is familiar with the iSER over iWARP implementation(s) ??? ***

 

In general, what do folks think ought to be done here - [2a], [2b] or
something else?

 

[WG chair hat on]

 

We do need to resolve this issue and reflect that resolution in a -09 iSER
draft before

RFC publication can be requested.

 

Thanks,
--David

 

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] ;
[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