RE: Target record not to span PDUs?

[JP Raghavendra Rao <Jp.Raghavendra@sun.com>]

> The approach you propose adds processing burden to every action on a target
> side to put a key=action into a PDU.  I envision the target side having
> contiguous memory to formulate the entire text response, and it then sends
> this in sequential PDUs. 

I may have to disagree with this statement. The response is dynamic and
is based on the request (the keys that the initiator is interested in)
and it is already doing some work here, in decoding the key and deciding
an appropriate action/value for the key. Therefore, I don't believe it is
either difficult or too much work to adjust the PDU to contain a complete
key/value pair in one PDU. If they span multiple PDUs, the initiator
has to do additional to work to coalesce them into meaningful pairs,
and I don't see any major gains in trying to do that.

-JP

> 
> Bob,
> 
> The record in question is a key=value pair. What Tow was asking is a about
> a way to avoid having to "concatenate
> strings" from two Text responses that carry the SendTargets answers one
> after another and we have stated that
> explicitly now.
> 
> Julo
> 
> Robert Snively <rsnively@Brocade.COM>@ece.cmu.edu on 22-08-2001 19:00:18
> 
> Please respond to Robert Snively <rsnively@Brocade.COM>
> 
> Sent by:  owner-ips@ece.cmu.edu
> 
> 
> To:   Tow Wang <Tow_Wang@adaptec.com>, Julian Satran/Haifa/IBM@IBMIL
> cc:   "'ips@ece.cmu.edu'" <ips@ece.cmu.edu>
> Subject:  RE: Target record not to span PDUs?
> 
> 
> 
> It sounds like there may be some confusion between "physical
> data unit" (the TCP/IP frame) and "iSCSI Protocol Data Unit"
> (the messaging unit for iSCSI).  I cannot see where Tom's
> problem arises, since Protocol Data Units are very well
> behaved and should not have the problems he is discussing.
> You cannot complete Protocol Data Unit processing until you
> know you have all of them and that useful information does not
> span them.  The assembly of protocol data units into useful
> complete messages should be done at a layer below that where
> you interpret the contiguous bytes of data in the context of
> the complete messages.  I think as a general rule that any
> iSCSI action should be able to span PDUs, including the
> Target Record.
> 
> Bob
> 
> > -----Original Message-----
> > From: Tow Wang [mailto:Tow_Wang@adaptec.com]
> > Sent: Tuesday, August 21, 2001 7:07 PM
> > To: 'Julian Satran'
> > Cc: 'ips@ece.cmu.edu'
> > Subject: Target record not to span PDUs?
> >
> >
> > Julian (and all):
> >
> > Hello. This is regarding draft 07; could we require that
> > target records NOT span across
> > PDU's if a text response for SendTargets is very long? Upon
> > reading appendix E, it seems
> > that a response (of 4096 bytes in length) could end with:
> >
> > [Begin data segment]
> > ...
> > TargetName=I.got.chopped.4096
> > TargetAddress=10.1.1.45
> > [End data segment]
> >
> > In the above case, one could not determine whether the
> > address is IP V4 or V6. Even if it
> > had had enough space to put in the whole address, port and
> > group tag, one cannot parse and
> > process the record until inspecting the data segment of the
> > next text response PDU, and
> > this would involve cumulative buffering, back-parsing, etc. I
> > think the above complexity
> > could be avoided, as I can't imagine any single record
> > exceeding 4096 bytes in length.
> >
> > Tow Wang
> >
> >
>