linux-kernel - Re: [PATCH 1/3] xen/blk[front|back]: Use the full FLUSH

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Date:	Sat, 10 Sep 2011 20:33:06 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	JBeulich@...ell.com, jeremy.fitzhardinge@...rix.com,
	axboe@...nel.dk
Subject: Re: [PATCH 1/3] xen/blk[front|back]: Use the full FLUSH | FUA
 instead of just FLUSH.

On Sat, Sep 10, 2011 at 02:08:49PM -0400, Christoph Hellwig wrote:
> On Fri, Sep 09, 2011 at 02:30:59PM -0400, Konrad Rzeszutek Wilk wrote:
> > During a FLUSH we can pass sector number that we want to
> > have flushed - which is what FUA requests are.
> 
> No, that is not the case.
> 
> REQ_FLUSH without data		-> pure flush
> REQ_FLUSH with data		-> preflush plus write

Excellent. So we have been doing it right all along.

> REQ_FUA				-> write and ranged postflush

Ah, somehow I was thinking that you can't write data with a
REQ_FLUSH, but that is nonsense as the block/blk-flush.c
explains in great details.

Will drop this patch - and thanks for clarifying it!
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