linux-kernel - Re: [PATCH] virtio_blk: support barriers without FLUSH feature

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Message-Id: <201006161126.32894.rusty@rustcorp.com.au>
Date:	Wed, 16 Jun 2010 11:26:32 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christoph Hellwig <hch@....de>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_blk: support barriers without FLUSH feature

On Tue, 15 Jun 2010 10:13:48 pm Christoph Hellwig wrote:
> If we want to support barriers with the cache=writethrough mode in qemu
> we need to tell the block layer that we only need queue drains to
> implement a barrier.  Follow the model set by SCSI and IDE and assume
> that there is no volatile write cache if the host doesn't advertize it.
> While this might imply working barriers on old qemu versions or other
> hypervisors that actually have a volatile write cache this is only a
> cosmetic issue - these hypervisors don't guarantee any data integrity
> with or without this patch, but with the patch we at least provide
> data ordering.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

Thanks, applied.

Cheers,
Rusty.
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