Return-Path: Received: from newbox.ece.cmu.edu (localhost [127.0.0.1]) by newbox.ece.cmu.edu (Cyrus v2.1.12) with LMTP; Tue, 22 Jul 2003 13:26:46 -0400 X-Sieve: CMU Sieve 2.2 Received: from osgood.ece.cmu.edu (OSGOOD.ECE.CMU.EDU [128.2.129.25]) by newbox.ece.cmu.edu (Postfix) with ESMTP id 2CD363008 for ; Tue, 22 Jul 2003 13:26:46 -0400 (EDT) Received: by osgood.ece.cmu.edu (Postfix, from userid 953) id 8832CB9; Tue, 22 Jul 2003 13:26:45 -0400 (EDT) Received: from sos.ece.cmu.edu (SOS.ECE.CMU.EDU [128.2.129.27]) by osgood.ece.cmu.edu (Postfix) with ESMTP id 354A6A5; Tue, 22 Jul 2003 13:26:23 -0400 (EDT) Received: by sos.ece.cmu.edu (Postfix) id 213F089D9; Tue, 22 Jul 2003 13:26:06 -0400 (EDT) Delivered-To: ips-outgoing@sos.ece.cmu.edu Received: from bache.ece.cmu.edu (BACHE.ECE.CMU.EDU [128.2.129.23]) by sos.ece.cmu.edu (Postfix) with ESMTP id 0EF9989D8 for ; Tue, 22 Jul 2003 13:26:06 -0400 (EDT) Received: by bache.ece.cmu.edu (Postfix) id D234C7F; Tue, 22 Jul 2003 13:26:05 -0400 (EDT) Delivered-To: ips-outgoing@ece.cmu.edu Received: by bache.ece.cmu.edu (Postfix, from userid 953) id ADF607C; Tue, 22 Jul 2003 13:26:05 -0400 (EDT) Received: from sos.ece.cmu.edu (SOS.ECE.CMU.EDU [128.2.129.27]) by bache.ece.cmu.edu (Postfix) with ESMTP id E542E9F for ; Tue, 22 Jul 2003 13:25:57 -0400 (EDT) Received: by sos.ece.cmu.edu (Postfix, from userid 363) id 9CDA689DC; Tue, 22 Jul 2003 13:25:57 -0400 (EDT) X-Original-To: ips@sos.ece.cmu.edu Delivered-To: ips@sos.ece.cmu.edu Received: from bache.ece.cmu.edu (BACHE.ECE.CMU.EDU [128.2.129.23]) by sos.ece.cmu.edu (Postfix) with ESMTP id 87B3889D8 for ; Tue, 22 Jul 2003 13:25:55 -0400 (EDT) Received: by bache.ece.cmu.edu (Postfix) id 0BC147B; Tue, 22 Jul 2003 13:25:55 -0400 (EDT) Delivered-To: ips@ece.cmu.edu Received: by bache.ece.cmu.edu (Postfix, from userid 953) id D3A719C; Tue, 22 Jul 2003 13:25:54 -0400 (EDT) Received: from mail.ivivity.com (unknown [64.238.111.99]) by bache.ece.cmu.edu (Postfix) with ESMTP id A10237C for ; Tue, 22 Jul 2003 13:25:49 -0400 (EDT) Received: by atlops.ivivity.com with Internet Mail Service (5.5.2653.19) id <3460WZA7>; Tue, 22 Jul 2003 13:25:49 -0400 Message-ID: From: Eddy Quicksall To: Dean Scoville , Julian Satran Cc: ips@ece.cmu.edu Subject: RE: CDB/PDU inconsistencies and residual counts Date: Tue, 22 Jul 2003 13:25:48 -0400 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2653.19) Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C35076.4ACDF340" Sender: owner-ips@ece.cmu.edu Precedence: bulk X-Spam-Status: No, hits=-11.9 required=5.0 tests=BAYES_10,HTML_50_60,HTML_FONT_COLOR_BLUE,ORIGINAL_MESSAGE version=2.50 X-Spam-Level: X-Spam-Checker-Version: SpamAssassin 2.50 (1.173-2003-02-20-exp) This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. ------_=_NextPart_001_01C35076.4ACDF340 Content-Type: text/plain My take is this: The overflow/underflow is determined by the SCSI layer. This is because the "expected data transfer length" gives the size of the initiators buffer and the CDB gives the size of the "attempted transfer". If the target is attempting to transfer too much, that would be an overflow. In some transports (like parallel SCSI) this is not determined by the target but is determined by the initiator driver or host adapter. In this case the target will try to stay in data-in phase to transfer all of the data. The initiator sees this as an overflow. Eddy -----Original Message----- From: Dean Scoville [mailto:dean.scoville@qlogic.com] Sent: Tuesday, July 22, 2003 12:43 PM To: Julian Satran Cc: ips@ece.cmu.edu Subject: CDB/PDU inconsistencies and residual counts Julian, The overflow/underflow and residual count values in Data-in and SCSI Response PDUs are set by the target based on the expected transfer length for the command, but should these values be set based on the CDB (SCSI layer) or based on the PDU "expected data transfer length" field (iSCSI layer)? For example, suppose an initiator sends a 4 block SCSI Read command but for some reason thinks the block size is 1024 bytes when in actuality the disk has 512 byte blocks. The SCSI Command PDU would have an "expected data transfer length" of value of 4096 bytes, but the target would actually return 2048 bytes (based on the true block size). Should the target set the underflow bit and return a residual count (based on the iSCSI PDU), or should it return no underflow and no residual count (based on the SCSI CDB)? The question comes up because I was running some iSCSI protocol test scripts where the PDU "expected transfer length" and the transfer length in the CDB were inconsistent in one of the scripts. Another example would be if the "allocation length" field in the CDB for an Inquiry command doesn't match the "expected data transfer length" field in the SCSI Command PDU. The script was in error and should be fixed, is there a desired target behavior in such situations, given that the CDB fields are not typically parsed by the iSCSI layer, the SCSI device may know nothing about iSCSI PDUs, and some middle-layer may or may not know about both. If the initiator detects that an underflow has occurred, based solely on the amount of data received and the "expected data transfer field" in the iSCSI PDU, but the target did not report an underflow or residual count in the SCSI response, is the initiator allowed/expected to report an underflow to the upper layers? Thanks, Dean Scoville ------_=_NextPart_001_01C35076.4ACDF340 Content-Type: text/html Content-Transfer-Encoding: quoted-printable CDB/PDU inconsistencies and residual counts

My take is this:

 

=

The overflow/underflow is = determined by the SCSI layer. This is because the "expected data transfer length" gives the size of the initiators buffer and the CDB gives the size of = the "attempted transfer". If the target is attempting to transfer too much, that would be an overflow.

 

=

In some transports (like parallel = SCSI) this is not determined by the target but is determined by the initiator = driver or host adapter. In this case the target will try to stay in data-in = phase to transfer all of the data. The initiator sees this as an = overflow.

 

=

Eddy

 

=

-----Original = Message-----
From: Dean Scoville [mailto:dean.scoville@qlogic.com]
Sent: Tuesday, July 22, = 2003 12:43 PM
To: Julian Satran
Cc: ips@ece.cmu.edu
Subject: CDB/PDU = inconsistencies and residual counts

 

Julian,
The overflow/underflow and residual count values in Data-in and =
SCSI Response PDUs are set by the target based on the expected =
transfer length for the command, but should these values be set = based
on the CDB (SCSI layer) or based on the PDU "expected data transfer = length"
field (iSCSI layer)?

For example, suppose an initiator sends a 4 = block SCSI Read command
but for some reason thinks the block size is 1024 bytes when in = actuality
the disk has 512 byte blocks. The SCSI Command PDU would have an =
"expected data transfer length" of value of 4096 bytes, but the target = would
actually return 2048 bytes (based on the true block size). Should the = target
set the underflow bit and return a residual count (based on the iSCSI = PDU),
or should it return no underflow and no residual count (based on the SCSI = CDB)?

The question comes up because I was running = some iSCSI protocol test
scripts where the PDU "expected transfer length" and the transfer = length
in the CDB were inconsistent in one of the scripts. =

Another example would be if the = "allocation length" field in the CDB for
an Inquiry command doesn't match the "expected data transfer = length" field
in the SCSI Command PDU.

The script was in error and should be fixed, = is there a desired target
behavior in such situations, given that the CDB fields are not typically = parsed
by the iSCSI layer, the SCSI device may know nothing about iSCSI = PDUs,
and some middle-layer may or may not know about both. =

If the initiator detects that an underflow = has occurred, based solely on the
amount of data received and the "expected data transfer field" in = the iSCSI PDU,
but the target did not report an underflow or residual count in the SCSI = response,
is the initiator allowed/expected to report an underflow to the upper = layers?

Thanks,

Dean Scoville

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