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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: Target record not to span PDUs?Julian, Not to be pedantic, but, again, the arbitrary decision to avoid the concatenation adds burden to the target side and restricts the future capability of key=values that exceed the max text PDU length. Again, the host side will need to buffer the input until it has all arrived anyway. Is there a stronger technical reason for this other than the avoidance of concatenation? 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. Having to search for where a key=value pair spans the PDU boundary is work. Furthermore, being able to span PDUs facilitates a simpler specification. Maybe Tow can explain the burden of concatenation. If Tow really doesn't care, can we go back to allowing the records to span PDUs? Does anyone else care about this? Stephen -----Original Message----- From: Julian Satran [mailto:Julian_Satran@il.ibm.com] Sent: Thursday, August 23, 2001 2:01 PM To: ips@ece.cmu.edu Subject: RE: Target record not to span PDUs? 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 > >
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