RE: Target record not to span PDUs?

[Robert Snively <rsnively@Brocade.COM>]

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
> 
>