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    Re: iSCSI: underrun with a check condition



    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
    **************************
    


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Last updated: Mon Feb 17 07:19:09 2003
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