Subject: Re: [PATCH net v2] virtio-net: unbreak vq resizing when coalescing is not negotiated

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 31 Jul 2024 08:14:43 -0400

On Wed, Jul 31, 2024 at 08:07:17PM +0800, Heng Qi wrote:
> >From the virtio spec:
> 
> 	The driver MUST have negotiated the VIRTIO_NET_F_VQ_NOTF_COAL
> 	feature when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET
> 	and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET.
> 
> The driver must not send vq notification coalescing commands if
> VIRTIO_NET_F_VQ_NOTF_COAL is not negotiated. This limitation of course
> applies to vq resize.
> 
> Fixes: f61fe5f081cf ("virtio-net: fix the vq coalescing setting for vq resize")
> Signed-off-by: Heng Qi <[email-masked]>
> Reviewed-by: Xuan Zhuo <[email-masked]>
> Acked-by: Eugenio Pé rez <[email-masked]>
> Acked-by: Jason Wang <[email-masked]>
> ---
> v1->v2:
>  - Rephrase the subject.
>  - Put the feature check inside the virtnet_send_{r,t}x_ctrl_coal_vq_cmd().
> 
>  drivers/net/virtio_net.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0383a3e136d6..2b566d893ea3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3658,6 +3658,9 @@ static int virtnet_send_rx_ctrl_coal_vq_cmd(struct virtnet_info *vi,
>  {
>  	int err;
>  
> +	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> +		return -EOPNOTSUPP;
> +
>  	err = virtnet_send_ctrl_coal_vq_cmd(vi, rxq2vq(queue),
>  					    max_usecs, max_packets);
>  	if (err)
> @@ -3675,6 +3678,9 @@ static int virtnet_send_tx_ctrl_coal_vq_cmd(struct virtnet_info *vi,
>  {
>  	int err;
>  
> +	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> +		return -EOPNOTSUPP;
> +
>  	err = virtnet_send_ctrl_coal_vq_cmd(vi, txq2vq(queue),
>  					    max_usecs, max_packets);
>  	if (err)
> @@ -3743,7 +3749,7 @@ static int virtnet_set_ringparam(struct net_device *dev,
>  			err = virtnet_send_tx_ctrl_coal_vq_cmd(vi, i,
>  							       vi->intr_coal_tx.max_usecs,
>  							       vi->intr_coal_tx.max_packets);
> -			if (err)
> +			if (err && err != -EOPNOTSUPP)
>  				return err;
>  		}
>

So far so good.
  
> @@ -3758,7 +3764,7 @@ static int virtnet_set_ringparam(struct net_device *dev,
>  							       vi->intr_coal_rx.max_usecs,
>  							       vi->intr_coal_rx.max_packets);
>  			mutex_unlock(&vi->rq[i].dim_lock);
> -			if (err)
> +			if (err && err != -EOPNOTSUPP)
>  				return err;
>  		}
>  	}

I don't get this one. If resize is not supported, we pretend it
was successful? Why?

> -- 
> 2.32.0.3.g01195cf9f