[Xen-devel] Re: [PATCH 1/3] xen/blk[front|back]: Use the full FLUSH | FUA instead of just FLUSH.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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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