On 10/30/19 4:12 PM, Bart Van Assche wrote:
On 10/30/19 1:30 AM, Hannes Reinecke wrote:
On 10/28/19 9:38 PM, Bart Van Assche wrote:
If the residual is changed from signed into unsigned, how is a SCSI
LLD expected to report the difference between residual overflow and
residual underflow to the SCSI core?
You don't have to. To quote RFC 3720 page 122:
bit 5 - (O) set for Residual Overflow. In this case, the Residual
Count indicates the number of bytes that were not transferred
because the initiator's Expected Data Transfer Length was not
sufficient. For a bidirectional operation, the Residual Count
contains the residual for the write operation.
IE the 'overflow' setting in the iSCSI command response is an
indicator that there _would_ be more data if the command request
_would_ have specified a larger buffer.
But as it didn't, the entire buffer was filled, and the overflow
counter is set.
Which, of course, is then ignored by the linux SCSI stack as the
request got all data, and the residual is set to zero.
Then it's left to the caller to re-send with a larger buffer if
required. But it's nothing the SCSI stack can nor should be attempting
on its own.
Hi Hannes,
I do not agree that reporting a residual overflow by calling
scsi_set_resid(..., 0) is acceptable. For reads a residual overflow
means that the length specified in the CDB (scsi_bufflen()) exceeds the
data buffer size (length of scsi_sglist()). I think it's dangerous to
report to the block layer that such requests completed successfully and
with residual zero.
But that is an error on submission, and should be aborted before it even
got send to the drive.
However, this does not relate to the residual, which is handled after
the command completes (and which sparked this entire thread ...).
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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HRB 21284 (AG Nürnberg)
