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SubjectRe: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk
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


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