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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Wed, 21 Nov 2018 14:03:59 +0100
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Subject: Re: [Qemu-devel] [[RFC v3 12/12] virtio: feature vhost-net support
 for packed ring
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To: wexu@redhat.com, qemu-devel@nongnu.org
Cc: jasowang@redhat.com, tiwei.bie@intel.com, jfreimann@redhat.com

Hi Wei,

On 10/11/18 4:08 PM, wexu@redhat.com wrote:
> From: Wei Xu <wexu@redhat.com>
> 
> (cherry picked from commit 305a2c4640c15c5717245067ab937fd10f478ee6)
> Signed-off-by: Wei Xu <wexu@redhat.com>
> (cherry picked from commit 46476dae6f44c6fef8802a4a0ac7d0d79fe399e3)
> Signed-off-by: Wei Xu <wexu@redhat.com>
> ---
>   hw/virtio/vhost.c          | 3 +++
>   hw/virtio/virtio.c         | 4 ++++
>   include/hw/virtio/virtio.h | 1 +
>   3 files changed, 8 insertions(+)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 9df2da3..de06d55 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -974,6 +974,9 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
>       }
>   
>       state.num = virtio_queue_get_last_avail_idx(vdev, idx);
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        state.num |= ((int)virtio_queue_packed_get_wc(vdev, idx)) << 31;

For next version, please note that we agreed to move the wrap counter
value at bit 15. DPDK vhost lib implemented it that way.