Re: iSCSI: underrun with a check condition

[Santosh Rao <santoshr@cup.hp.com>]

Julian,

The initiator SCSI LLP would not know if the device server processed 
the command successfully or not, except for the u/o/resid information. If the
device server did not process the command and returned a RECOVERED ERROR check
condition on it, the host may process the completion as if the command had
completed successfully, since the resid field will be 0 and the u/o bits not
set.

Such behaviour can result in a corrupt read due to the read being completed
with success, but no data having been read into the read data buffer. 

SAM-2 Section 5.3.2 is only discussing SCSI status precedence. It does not
explain the resid reporting precedence compared to SCSI status. 

Regards,
Santosh



> 
> Santosh,
> 
> For any check condition in which the target did process the command this
> is the expected behavior.
> The example Eddy gave involves a target that due to ACA or BUSY does not
> initiate processing the command.
> In this case the target provider does not HAVE TO set the U/O bits (and
> the associated values).
> The relevant piece of information appears in SAM2 5.3.2 that indicates
> that status precedence.
> Obviously a target MAY set the U/O bits although  I doubt that an
> initiator will look them up.
> 
> Regards,
> Julo
> 
> 
> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu] On Behalf Of
> Santosh Rao
> Sent: 16 February, 2003 23:28
> To: Eddy Quicksall
> Cc: "Ips@Ece.Cmu.Edu (ips@ece.cmu.edu)"
> Subject: Re: iSCSI: underrun with a check condition
> 
> 
> Eddy,
> 
> Yes, anytime the amount of data transferred does not match the data
> transfer length specified, the target must set the U bit or O bit,
> depending on whether an underflow or overflow occurred.
> 
> A recovered error check condition may be returned as the response to a
> scsi command which was processed to completion. The recovered error
> indicates that a previous command completed successfully with some
> recovery action by the device server and the sense data provides
> additional details on that previous command.
> 
> The current command on which a recovered error check condition was
> returned may have been processed to completion, or experienced some
> underflow or overflow. This information must be conveyed by the target
> in the iscsi scsi response pdu using the appropriate fields to describe
> the underflow or overflow.
> 
> Thanks,
> Santosh
> 
> 
> > Should the target set the U bit when it gives a check condition to a 
> > data-in command?
> >  
> >  
> > Eddy
> 
> 


-- 
**************************
Santosh Rao
HP-UX SCSI Team,
Hewlett Packard, Cupertino
**************************