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

From: Shaohua Li
Date: Fri Feb 07 2014 - 19:55:27 EST

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.

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