Re: [RFC] libata new EH document

Jeff Garzik
2005-09-01T02:22:35Z

Tejun Heo wrote:
> IMHO, it's a good idea to maintain one qc to one ATA/ATAPI command
> mapping as long as possible. And, in the suggested framework, it's
> guaranteed that no other command can come inbetween CHECK_SENSE and
> REQUEST_SENSE.
>
> Requesting sense from EH, calling scsi_decide_disposition() on the
> sense and following the verdict should achieve the same effect as
> emulating autosense. Is there any compelling reason to break one qc to
> one command mapping?

Yes, you should have one qc <-> one ATA/ATAPI command. That's why, in
the NCQ scenario, I wanted to make sure that one qc was always reserved
for error handling: REQUEST SENSE or READ LOG EXT, most importantly.

For SAT layer MODE SELECT translations, that implies multiple calls to
qc_new/qc_issue/qc_complete before completing the overall SCSI command.
The same for handling sata_sil mod15write: I am beginning to feel
like the mod15write workaround might be best implemented in a manner
that caused libata-scsi (not sata_sil) to create/issue/complete multiple
ATA commands.

The only problem you run into is that a qc may be active during EH, when
you need another qc. So avoiding recursive details becomes an issue.

Jeff