RE: Data in SCSI Response or SCSI Data

["Douglas Otis" <dotis@sanlight.net>]

Bob,

SAM-2
"As specified in clause 5, the application client may request autosense
service for any SCSI command. If supported
by the protocol and logical unit and requested by the application client,
the device server shall only return sense
data in this manner coincident with the completion of a command with a
status of CHECK CONDITION."

SSC
"If the suppress incorrect length indicator (SILI) bit is one and the FIXED
bit is zero, the device server shall:
a) Report CHECK CONDITION status for an incorrect length condition only if
the overlength condition
exists and the BLOCK LENGTH field in the mode parameter block descriptor is
nonzero (see SPC-2); or
b) not report CHECK CONDITION status if the only error is the underlength
condition, or if the only error
is the overlength condition and the BLOCK LENGTH field of the mode
parameters block descriptor is zero.

NOTE 9 Since the residue information normally provided in the INFORMATION
field of the sense data may not
be available when the SILI bit is set, other methods for determining the
actual block length should be used
(e.g. including length information in the data block).

If the SILI bit is one and the FIXED bit is one, the device server shall
terminate the command with CHECK
CONDITION status and the sense key shall be set to ILLEGAL REQUEST with an
additional sense code
and an additional sense code qualifier of INVALID FIELD IN CDB.

If the SILI bit is zero and an incorrect length block is read, CHECK
CONDITION status shall be returned
and the ILI and VALID bits shall be set to one in the sense data with an
additional sense code and an
additional sense code qualifier of NO ADDITIONAL SENSE INFORMATION. Upon
termination, the
logical position shall be after the incorrect length block (end-of-partition
side). If the FIXED bit is one, the
INFORMATION field shall be set to the requested transfer length minus the
actual number of blocks read
(not including the incorrect length block). If the FIXED bit is zero, the
INFORMATION field shall be set to the
requested transfer length minus the actual block length. Logical units that
do not support negative values
shall set the INFORMATION field to zero if the overlength condition exists."

From these definitions, do not expect any defined information regarding
residue without a Check Condition.  The residue of iSCSI within the Read PDU
0x45 is not SCSI related nor does it represent the underlength condition you
suggest.  Such underlength data is normally lost and uninteresting if the
SILI bit is set.

Doug

> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> Robert Reynolds
> Sent: Monday, September 11, 2000 8:07 AM
> To: 'Stephen Bailey'; ips@ece.cmu.edu
> Subject: RE: Data in SCSI Response or SCSI Data
>
>
> > -----Original Message-----
> > From: Stephen Bailey [mailto:steph@cs.uchicago.edu]
> > Sent: Wednesday, September 06, 2000 5:45 PM
> > To: ips@ece.cmu.edu
> > Subject: Re: Data in SCSI Response or SCSI Data
> >
> >
> > > When do you get GOOD status and residual counts on a read?
> > What is causing
> > > the target to get the length wrong?
> >
> > One example is an INQUIRY command.  The inquiry data length is
> > target-specific.  Typically the CDB allocation length (and DL) are set
> > to some arbitrary large value (0xff), and the target sends back
> > everything it has.  The transfer ends with success status.
> >
> > There can certainly be transfer residual and no SCSI error status.
>
>
>   Another example is on variable block tape reads.  The Initiator
>   uses an arbitrary size to read the block and the target sends all
>   the data in that block.  In many cases the amount of data returned
>   is less than the amount of data asked for but it is still a GOOD
>   status.
>
>     Bob
>