Re: [PATCH v3] Add support for SCT Write Same

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On Tue, Jun 21, 2016 at 9:43 PM, Martin K. Petersen
<martin.petersen@xxxxxxxxxx> wrote:
>>>>>> "Shaun" == Shaun Tancheff <shaun@xxxxxxxxxxxx> writes:
>
> Shaun> SATA drives may support write same via SCT. This is useful for
> Shaun> setting the drive contents to a specific pattern (0's).
>
> As indicated a while back, my preference would be for you to add support
> for REPORT SUPPORTED OPERATION CODES. It's fine that you keep the RSOC
> response simple and only list WRITE SAME(10/16). But I want to avoid
> having different heuristics for libata's SCSI-ATA translation and for
> hardware controller ditto.
>
> Shaun> If UNMAP is not set or TRIM is not available
>
> Please do not conflate the two. We have the appropriate fallbacks at the
> block layer. It happens to be the same command descriptor but it is two
> very different implementations at the device level.
>
> If the UNMAP bit is set you need to issue a DSM TRIM. If the device does
> not support TRIM you need to return ILLEGAL REQUEST/INVALID FIELD IN
> CDB.
>
> If the UNMAP bit is not set then it's a regular WRITE SAME and should be
> issued using SCT WRITE SAME. If the device does not support SCT WRITE
> SAME you need to return ILLEGAL REQUEST/INVALID FIELD IN CDB.

Thanks for the clarification and the review.
I will work on support for REPORT SUPPORTED OPERATION CODES and
handle the WRITE SAME following the UNMAP as you described.

Thanks!

> --
> Martin K. Petersen      Oracle Linux Engineering



-- 
Shaun Tancheff
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