RE>RE- SCSI-3 Reseved Field
Charles Monia, SHR3-2/W3, 237-6757 29-Apr-1994 1453
monia at starch.enet.dec.com
Fri Apr 29 11:54:18 PDT 1994
Jim McGrath wrote:
I do not see how the suggestions address Bob's original point - the sender
should be instructed not to set reserved bits, but the target (or logical unit -
in my devices they are one in the same) should not be required to check them.
Checking for reserved bits is a time consuming process (or gate consuming if
done in hardware) - I agree with Bob that there is little reason to perform this
cheack in the real world.
On parameter data, I do not think SCSI-2 requires any checking of parameter data
today. I would be opposed to an extension that would break de fecto SCSI-3
software (i.e. exiting SCSI-2 software).
I thought Bob's issue pertained to checking FCP data structures that would not
be visible to the logical unit. The purpose of the proposal was to define the
data structures for which testing was required in a way that clearly excludes
With regard to SCSI-2 requirements, the following is from rev 10h , pp 72 of
the SCSI-2 spec. I've included the major section headings to establish the
context in which the quoted paragraph appears.
"6. SCSI Commands and Status
6.1 Command Implementation Requirements
Reserved bits fields bytes and code values are set aside for future
standardization. Their use and interpretation may be specified by future
extensions to this standard. A reserved bit field or byte shall be set to zero
or in accrodance with a future extension to this standard. A target that
receives a reserved bit, field or byte that is not zero or receives a reserved
code value shall terminate the command with a CHECK CONDITION status. and the
sense key shall be set to ILLEGAL REQUEST. It shall also be acceptable for a
target to interpret a bit field, byte or code value in accordance with a future
extension to this standard."
As I read the above, the enforcement requirements seem to apply both to the
command descriptor block and parameter data. At least the proposed SCSI-3
wording was based on that assumption. At any rate, I believe some direction from
the committee is required here.
BTW: SAM goes out of its way to distinguish between "target" and "logical unit".
In a number of places within section 6 of the SCSI-2 spec, , the word "target"
is incorrectly used in place of "logical unit". I had assumed the use of target
in the quoted paragraph was another one of those instances.
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