netdev - Re: [PATCH RFC 6/9] veth: Add ndo_xdp

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Date:   Wed, 25 Apr 2018 22:24:52 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toshiaki Makita <toshiaki.makita1@...il.com>
Cc:     brouer@...hat.com, netdev@...r.kernel.org,
        Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Subject: Re: [PATCH RFC 6/9] veth: Add ndo_xdp_xmit

On Tue, 24 Apr 2018 23:39:20 +0900
Toshiaki Makita <toshiaki.makita1@...il.com> wrote:

> +static int veth_xdp_xmit(struct net_device *dev, struct xdp_frame *frame)
> +{
> +	struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
> +	int headroom = frame->data - (void *)frame;
> +	struct net_device *rcv;
> +	int err = 0;
> +
> +	rcv = rcu_dereference(priv->peer);
> +	if (unlikely(!rcv))
> +		return -ENXIO;
> +
> +	rcv_priv = netdev_priv(rcv);
> +	/* xdp_ring is initialized on receive side? */
> +	if (rcu_access_pointer(rcv_priv->xdp_prog)) {
> +		err = xdp_ok_fwd_dev(rcv, frame->len);
> +		if (unlikely(err))
> +			return err;
> +
> +		err = veth_xdp_enqueue(rcv_priv, veth_xdp_to_ptr(frame));
> +	} else {
> +		struct sk_buff *skb;
> +
> +		skb = veth_build_skb(frame, headroom, frame->len, 0);
> +		if (unlikely(!skb))
> +			return -ENOMEM;
> +
> +		/* Get page ref in case skb is dropped in netif_rx.
> +		 * The caller is responsible for freeing the page on error.
> +		 */
> +		get_page(virt_to_page(frame->data));

I'm not sure you can make this assumption, that xdp_frames coming from
another device driver uses a refcnt based memory model. But maybe I'm
confused, as this looks like an SKB receive path, but in the
ndo_xdp_xmit().


> +		if (unlikely(veth_forward_skb(rcv, skb, false) != NET_RX_SUCCESS))
> +			return -ENXIO;
> +
> +		/* Put page ref on success */
> +		page_frag_free(frame->data);
> +	}
> +
> +	return err;
> +}


-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer