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

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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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