Subject: Re: [PATCH net-next v2 05/14] virtio_net: introduce xdp res enums

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 21 Apr 2023 03:00:15 -0400

On Tue, Apr 18, 2023 at 02:53:18PM +0800, Xuan Zhuo wrote:
> virtnet_xdp_handler() is to process all the logic related to XDP. The
> caller only needs to care about how to deal with the buf. So this commit
> introduces new enums:
> 
> 1. VIRTNET_XDP_RES_PASS: make skb by the buf
> 2. VIRTNET_XDP_RES_DROP: xdp return drop action or some error, caller
>    should release the buf
> 3. VIRTNET_XDP_RES_CONSUMED: xdp consumed the buf, the caller doesnot to
>    do anything
> 
> Signed-off-by: Xuan Zhuo <[email-masked]>

I am not excited about using virtio specific enums then translating
to standard ones.

> ---
>  drivers/net/virtio_net.c | 42 ++++++++++++++++++++++++++--------------
>  1 file changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0fa64c314ea7..4dfdc211d355 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -301,6 +301,15 @@ struct padded_vnet_hdr {
>  	char padding[12];
>  };
>  
> +enum {
> +	/* xdp pass */
> +	VIRTNET_XDP_RES_PASS,
> +	/* drop packet. the caller needs to release the page. */
> +	VIRTNET_XDP_RES_DROP,
> +	/* packet is consumed by xdp. the caller needs to do nothing. */
> +	VIRTNET_XDP_RES_CONSUMED,
> +};
> +
>  static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
>  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
>  
> @@ -803,14 +812,14 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  
>  	switch (act) {
>  	case XDP_PASS:
> -		return act;
> +		return VIRTNET_XDP_RES_PASS;
>  
>  	case XDP_TX:
>  		stats->xdp_tx++;
>  		xdpf = xdp_convert_buff_to_frame(xdp);
>  		if (unlikely(!xdpf)) {
>  			netdev_dbg(dev, "convert buff to frame failed for xdp\n");
> -			return XDP_DROP;
> +			return VIRTNET_XDP_RES_DROP;
>  		}
>  
>  		err = virtnet_xdp_xmit(dev, 1, &xdpf, 0);
> @@ -818,19 +827,20 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  			xdp_return_frame_rx_napi(xdpf);
>  		} else if (unlikely(err < 0)) {
>  			trace_xdp_exception(dev, xdp_prog, act);
> -			return XDP_DROP;
> +			return VIRTNET_XDP_RES_DROP;
>  		}
> +
>  		*xdp_xmit |= VIRTIO_XDP_TX;
> -		return act;
> +		return VIRTNET_XDP_RES_CONSUMED;
>  
>  	case XDP_REDIRECT:
>  		stats->xdp_redirects++;
>  		err = xdp_do_redirect(dev, xdp, xdp_prog);
>  		if (err)
> -			return XDP_DROP;
> +			return VIRTNET_XDP_RES_DROP;
>  
>  		*xdp_xmit |= VIRTIO_XDP_REDIR;
> -		return act;
> +		return VIRTNET_XDP_RES_CONSUMED;
>  
>  	default:
>  		bpf_warn_invalid_xdp_action(dev, xdp_prog, act);
> @@ -839,7 +849,7 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  		trace_xdp_exception(dev, xdp_prog, act);
>  		fallthrough;
>  	case XDP_DROP:
> -		return XDP_DROP;
> +		return VIRTNET_XDP_RES_DROP;
>  	}
>  }
>  
> @@ -987,17 +997,18 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  		act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
>  
>  		switch (act) {
> -		case XDP_PASS:
> +		case VIRTNET_XDP_RES_PASS:
>  			/* Recalculate length in case bpf program changed it */
>  			delta = orig_data - xdp.data;
>  			len = xdp.data_end - xdp.data;
>  			metasize = xdp.data - xdp.data_meta;
>  			break;
> -		case XDP_TX:
> -		case XDP_REDIRECT:
> +
> +		case VIRTNET_XDP_RES_CONSUMED:
>  			rcu_read_unlock();
>  			goto xdp_xmit;
> -		default:
> +
> +		case VIRTNET_XDP_RES_DROP:
>  			goto err_xdp;
>  		}
>  	}
> @@ -1324,18 +1335,19 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  		act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
>  
>  		switch (act) {
> -		case XDP_PASS:
> +		case VIRTNET_XDP_RES_PASS:
>  			head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
>  			if (unlikely(!head_skb))
>  				goto err_xdp_frags;
>  
>  			rcu_read_unlock();
>  			return head_skb;
> -		case XDP_TX:
> -		case XDP_REDIRECT:
> +
> +		case VIRTNET_XDP_RES_CONSUMED:
>  			rcu_read_unlock();
>  			goto xdp_xmit;
> -		default:
> +
> +		case VIRTNET_XDP_RES_DROP:
>  			break;
>  		}
>  err_xdp_frags:
> -- 
> 2.32.0.3.g01195cf9f