SMP frame - issue with maximum number of valid data bytes

Rich Deglin richd at serverengines.com
Mon Jan 28 13:30:42 PST 2008


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Ah yes, Rob, but which tables are the correct ones, those in section 9 or
those in section 10? Or are you suggesting that both sets of tables be
reworked?
Thanks.
  _____  
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Elliott,
Robert (Server Storage)
Sent: Sunday, January 27, 2008 6:48 PM
To: t10 at t10.org
Subject: RE: SMP frame - issue with maximum number of valid data bytes
We don't really use "fill bytes" in SMP, since the request and response
frames are always defined as containing structures that are multiples of 4
bytes.	The only one that does not do so is the ZONED BROADCAST request, but
it already defines a "PAD" field on its own to round up to a multiple of 4
bytes.
Removing the "fill bytes" concept would be a good letter ballot comment on
sas2r14.
-- 
Rob Elliott, elliott at hp.com 
Hewlett-Packard Industry Standard Server Storage Advanced Technology 
  _____  
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Rich Deglin
Sent: Thursday, January 24, 2008 7:32 PM
To: t10 at t10.org
Subject: SMP frame - issue with maximum number of valid data bytes
SAS 2 (r13) section 9.4.3, I think, clearly shows that a maximum length SMP
RESPONSE frame consists of the following:
1 byte FRAME TYPE
1024 bytes RESPONSE BYTES
3 fill bytes
4 bytes CRC
In my reading of this section, this means that an SMP RESPONSE frame with a
maximum length RESPONSE BYTES field has NO MORE THAN 1025 valid data bytes
plus 3 fill bytes plus 4 CRC bytes = 1032 total bytes. The "header"
mentioned in section 10.4.3.2 is not shown here.
Section 10.4.3.2 conflicts with this. It states that a maximum length SMP
RESPONSE frame consists of the following:
1 byte FRAME TYPE
1 byte FUNCTION
1 byte FUNCTION RESULT
1 byte RESPONSE LENGTH
1024 bytes RESPONSE BYTES
0 fill bytes
4 bytes CRC
In my reading of this section, this means that an SMP RESPONSE frame with a
maximum length RESPONSE BYTES field has EXACTLY 1028 valid data bytes plus 0
fill bytes plus 4 CRC bytes = 1032 total bytes. A 4 byte "header" is
mentioned in the text of this section but is not explicitly defined, which I
would contend is an oversight in the document.
The SMP REQUEST frame descriptions demonstrate the same issue.
Please explain the apparent conflict. If there is a real problem here in the
spec, is a proposal necessary to correct it?
Also note that the same issues exist in the SAS 1.1 spec, but I am guessing
that no problems occurred in practice, due to the fact that the lengths of
the SAS 1.1 defined SMP REQUESTs and RESPONSEs do not get anywhere near the
limits.
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