SRP Sense Buffer Length (NO RESTRICTIONS IN PROTOCOLS)
rsnively at Brocade.COM
Wed Mar 13 13:02:12 PST 2002
* From the T10 Reflector (t10 at t10.org), posted by:
* Robert Snively <rsnively at brocade.com>
In skimming this, I thought you might like to know:
These are the requirements specified by FCP-2:
a) 126.96.36.199 requires additional CDB length to be a multiple of 4.
b) 188.8.131.52 and 9.2.2 require all data frames to
begin on a 4-byte boundary
as specified by their relative offset (and the FCP_XFER_RDY
parameters). The last one need not end on a
4-byte boundary, although in FC, pad bytes may
need to be included at the frame level. Implicitly,
all sequences except the last need to be 0 modulo 4 in length.
c) 8.3 requires retries start on 4-byte boundaries.
A requirement NOT made by FCP-2 is that the sense information
be a multiple of 4-bytes. There is no such requirement in
SPC-2, nor in FC-PLDA. There is similarly no requirement that
lengths be counted by units of 4. I could similarly find no
such limitation in SPI-4, since pad bytes are always available
to control ending boundaries.
I think this requirement comes from some previous out-of-context
discussions and is not necessary or desirable for SRP.
Bob Snively e-mail: rsnively at brocade.com
Brocade Communications Systems phone: 408 487 8135
1745 Technology Drive
San Jose, CA 95110
> -----Original Message-----
> From: Patrick Fitzpatrick [mailto:PFitzpatrick at jni.com]
> Sent: Thursday, March 07, 2002 3:46 PM
> To: 'Edward A. Gardner'; t10 at t10.org
> Subject: RE: SRP Sense Buffer Length
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Patrick Fitzpatrick <PFitzpatrick at JNI.com>
> Hi Edward,
> thanks for the background. I am fine with the clarification. It
> would have been nice for the SRP doc to have stated that the
> length should
> be rounded up and unspecified padded used. There is a possibility of
> confusion because of the rules for treating sense data when
> it will not fit
> within the IU, i.e truncate. This led me to infer that if
> sense data was not
> multiple of 4 bytes long that I should truncate the sense data.
> -----Original Message-----
> From: Edward A. Gardner [mailto:eag at ophidian.com]
> Sent: Thursday, March 07, 2002 3:41 PM
> To: Patrick Fitzpatrick; t10 at t10.org
> Subject: Re: SRP Sense Buffer Length
> > STP T10 Rev 10 Page 37 Line 30 states
> >SRP RSP IU: "The SENSE DATA LIST LENGTH field shall only
> contain lengths
> >that are a multiple of 4."
> >I am confused as to the reasoning for this because it seems
> that most sense
> >data is 18 bytes long. There is nothing to say what should
> be done is the
> >actual sense data is not a multiple of 4 bytes long. Should
> the data be
> >trunacated down to the lowest length multiple of 4 or should
> it be rounded
> >up. What happens to the (1 to 3) undefined bytes that are
> now in the sense
> >buffer if rounding up is the solution.
> >I do not see the need for this restriction, other than for
> alignment, but
> >sense data is at the end of the IU, alignment should not be an issue.
> The SENSE DATA LIST LENGTH field specifies the length of the
> SENSE DATA
> field, *not* the length of the sense data. The sense data is
> self-describing, including its own length field. When 18
> bytes of sense
> data are returned, the SENSE DATA field contains 18 bytes of
> sense data and
> two bytes of padding. SRP doesn't specify the contents of
> the padding.
> They are not part of the sense data.
> FCP/FCP-2 and SPI-n IUs share this "feature" and use almost identical
> wording. It arises from a requirement to keep FCP / SPI-n /
> SRP IUs 32-bit
> aligned. It is just unfortunate (and a historical accident)
> that standard
> sense data is 18 bytes, which is not 32-bit aligned.
> If you want to pursue this further, there is an SRP
> conference call at 9 AM
> PST tomorrow (Friday Mar 8).
> Edward A. Gardner eag at ophidian.com
> Ophidian Designs 719 593-8866 voice
> 1262 Hofstead Terrace 719 593-8989 fax
> Colorado Springs, CO 80907 719 210-7200 cell
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