Re: [PATCH v2] libata: add support for NCQ commands for SG interface

[Tejun Heo]

On Mon, Nov 16, 2015 at 08:47:19AM -0500, Mark Lord wrote:
> On 15-10-27 01:49 AM, vinayak.kale@xxxxxxxxx wrote:
> >From: Vinayak Kale <vinayak.kale@xxxxxxxxxxx>
> >
> >This patch is needed to make NCQ commands with FPDMA protocol value
> >(eg READ/WRITE FPDMA) work over SCSI Generic (SG) interface.
> ..
> >+	/* For NCQ commands with FPDMA protocol, copy the tag value */
> >+	if (tf->protocol == ATA_PROT_NCQ)
> >+		tf->nsect = qc->tag << 3;
> >+
> 
> 
> What prevents the qc-tag value here from conflicting with in-flight I/O
> using the exact same qc-tag ??

The SG command doesn't set the tag, it's being set from an allocated
qc which can't otherwise be in-flight.

Thanks.

-- 
tejun
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