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

["Martin K. Petersen" <martin.petersen@oracle.com>]

>>>>> "Shaun" == Shaun Tancheff <shaun@tancheff.com> 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.

-- 
Martin K. Petersen	Oracle Linux Engineering