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 07:54:11 -0400

On Fri, Apr 21, 2023 at 03:24:00PM +0800, Xuan Zhuo wrote:
> On Fri, 21 Apr 2023 03:00:15 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > 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.
> 
> 
> My fault, my expression is not very complete.
> 
> This is not a replacement, but just want to say, there are only three cases of
> virtnet_xdp_handler. Caller only needs to handle this three cases. Instead
> of paying attention to the detailed return results of XDP.
> 
> In addition, virtnet_xdp_handler returns XDP_TX, but in fact, the work of XDP_TX
> is already done in Virtnet_xdp_handler. Caller does not need to do anything for
> XDP_TX, giving people a feeling, XDP_TX does not need to be processed. I think
> it is not good.
> 
> Thanks.

I don't really get it, sorry. If it's possible to stick to
XDP return codes, that is preferable.

> 
> 
> >
> > > ---
> > >  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
> >