linux-kernel - Re: [PATCH 1/1] block: rework flush sequencing for blk-mq

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Message-ID: <20140208005507.GA1766@kernel.org>
Date:	Sat, 8 Feb 2014 08:55:07 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] block: rework flush sequencing for blk-mq

On Fri, Feb 07, 2014 at 06:19:15AM -0800, Christoph Hellwig wrote:
> On Fri, Feb 07, 2014 at 09:18:27AM +0800, Shaohua Li wrote:
> > Reusing the tag for flush request is considered before. The problem is driver
> > need get a request from a tag, reusing tag breaks this. The possible solution
> > is we provide a blk_mq_tag_to_request, and force driver uses it. And in this
> > function, if tag equals to flush_rq tag, we return flush_request.
> 
> If we want to support tag to request reverse mapping we defintively
> need to do this in the core, at which point special casing flush_rq
> there is easy.
> 
> Which driver needs the reverse mapping? Neither virtio_blk nor null_blk
> seem to and I've not seen any other conversions submitted except for the
> scsi work.

Yep, none driver needs it. But reverse mapping is the one of the points we use
tag, so better we prepare it.

Thanks,
Shaohua
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