struct scsi_cmnd --> underflow

[Shailesh Parulekar]

Hi,

I am writing a SCSI LLD and have a query regarding handling of
underflow errors.

In function sd_prep_fn (sd.c) the code populates scsi command pointer
(SCpnt) and it's cmnd.
Going ahead it also sets the total length to be transferred in the
scsi data buffer (SCpnt->sdb.length = this_count * sdp->sector_size).
Here 'this_count' looks to be the nr_sectors. This assignment looks
fine too.
But later when assigning the 'underflow' field of SCpnt, the
assignment uses a hard-coded bit shift (SCpnt->underflow = this_count
<< 9). Is this valid? OR
should it be: SCpnt->underflow = this_count << sdp->sector_size?

So, if the sector size exported by the target device is greater than
512 (4K in our case), the SCpnt->underflow is not same as SCpnt-
>sdb.length. The later is 8 times bigger. So if I get a read of say 8K
the 'underflow' is set only to 1K. Now, if the target say returns only
2K of data for this read, the amount of data transferred is not less
than residual (1K in this case). So is the LLD not supposed to return
(DID_ERROR << 16) in 'result' for this case (assuming target returns
result == GOOD)?

Please let me know.

thanks,
--shailesh