From mboxrd@z Thu Jan  1 00:00:00 1970
From: Asias He <asias@redhat.com>
Subject: Re: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk
Date: Mon, 30 Jul 2012 12:43:12 +0800
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig <hch@lst.de>
List-Id: virtualization@lists.linuxfoundation.org

On 07/28/2012 02:42 PM, Paolo Bonzini wrote:
>>> I'm not sure what the correct behavior for bio & cacheflush is, if
>>> any.
>>
>> REQ_FLUSH is not supported in the bio path.
>
> Ouch, that's correct:
>
> @@ -414,7 +529,7 @@ static void virtblk_update_cache_mode(struct virtio_device *vdev)
>   	u8 writeback = virtblk_get_cache_mode(vdev);
>   	struct virtio_blk *vblk = vdev->priv;
>
> -	if (writeback)
> +	if (writeback && !use_bio)
>   		blk_queue_flush(vblk->disk->queue, REQ_FLUSH);
>   	else
>   		blk_queue_flush(vblk->disk->queue, 0);
>
> then it is not safe against power losses.

Yes. Something like this:

   qemu -drive file=foo.img,cache=writeback/unsafe

is not safe against power losses also?

I think we can add REQ_FLUSH & REQ_FUA support to bio path and that 
deserves another patch.

-- 
Asias