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Date: Fri, 14 Jun 2013 10:23:02 -0400
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 04/13] virtio-blk: implement
	BlockDevOps->drain_threads_cb()
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Ping Fan Liu <pingfank@linux.vnet.ibm.com>, qemu-devel@nongnu.org

Il 14/06/2013 05:48, Stefan Hajnoczi ha scritto:
> Drain and stop the dataplane thread when bdrv_drain_all() is called.
> Note that the thread will be restarted in virtio_blk_handle_output() the
> next time the guest kicks the virtqueue.

Long term I still think we want to move towards

    aio_lock(bs)
    bdrv_drain(bs)
    ...
    aio_unlock(bs)

but this approach works well at this point.  It is a hack, but a very
smart one. :)

Add a comment in the code about what will start the dataplane thread,
though.

Paolo

> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/block/virtio-blk.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index cf12469..f9c2b79 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -618,8 +618,20 @@ static void virtio_blk_resize(void *opaque)
>      virtio_notify_config(vdev);
>  }
>  
> +static void virtio_blk_drain_threads(void *opaque)
> +{
> +#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
> +    VirtIOBlock *s = VIRTIO_BLK(opaque);
> +
> +    if (s->dataplane) {
> +        virtio_blk_data_plane_stop(s->dataplane);
> +    }
> +#endif
> +}
> +
>  static const BlockDevOps virtio_block_ops = {
>      .resize_cb = virtio_blk_resize,
> +    .drain_threads_cb = virtio_blk_drain_threads,
>  };
>  
>  void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk)
>