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

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Message-ID: <20151116153133.GA18894@mtj.duckdns.org>
Date:	Mon, 16 Nov 2015 10:31:33 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Mark Lord <kernel@...rt.ca>
Cc:	vinayak.kale@...il.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org, sumit.g.gupta@...gate.com,
	Vinayak Kale <vinayak.kale@...gate.com>
Subject: Re: [PATCH v2] libata: add support for NCQ commands for SG interface

On Mon, Nov 16, 2015 at 08:47:19AM -0500, Mark Lord wrote:
> On 15-10-27 01:49 AM, vinayak.kale@...il.com wrote:
> >From: Vinayak Kale <vinayak.kale@...gate.com>
> >
> >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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