Re: [PATCH v2 7/9] virtio_net: build skb from multi-buffer xdp

Jason Wang
2022-12-27T07:32:40Z

在 2022/12/20 22:14, Heng Qi 写道:
> This converts the xdp_buff directly to a skb, including
> multi-buffer and single buffer xdp. We'll isolate the
> construction of skb based on xdp from page_to_skb().
>
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 50 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 50 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9f31bfa7f9a6..4e12196fcfd4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -948,6 +948,56 @@ static struct sk_buff *receive_big(struct net_device *dev,
> return NULL;
> }
>
> +/* Why not use xdp_build_skb_from_frame() ?
> + * XDP core assumes that xdp frags are PAGE_SIZE in length, while in
> + * virtio-net there are 2 points that do not match its requirements:
> + * 1. The size of the prefilled buffer is not fixed before xdp is set.
> + * 2. When xdp is loaded, virtio-net has a hole mechanism (refer to
> + * add_recvbuf_mergeable()), which will make the size of a buffer
> + * exceed PAGE_SIZE.

Is point 2 still valid after patch 1?

Other than this:

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

> + */
> +static struct sk_buff *build_skb_from_xdp_buff(struct net_device *dev,
> + struct virtnet_info *vi,
> + struct xdp_buff *xdp,
> + unsigned int xdp_frags_truesz)
> +{
> + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> + unsigned int headroom, data_len;
> + struct sk_buff *skb;
> + int metasize;
> + u8 nr_frags;
> +
> + if (unlikely(xdp->data_end > xdp_data_hard_end(xdp))) {
> + pr_debug("Error building skb as missing reserved tailroom for xdp");
> + return NULL;
> + }
> +
> + if (unlikely(xdp_buff_has_frags(xdp)))
> + nr_frags = sinfo->nr_frags;
> +
> + skb = build_skb(xdp->data_hard_start, xdp->frame_sz);
> + if (unlikely(!skb))
> + return NULL;
> +
> + headroom = xdp->data - xdp->data_hard_start;
> + data_len = xdp->data_end - xdp->data;
> + skb_reserve(skb, headroom);
> + __skb_put(skb, data_len);
> +
> + metasize = xdp->data - xdp->data_meta;
> + metasize = metasize > 0 ? metasize : 0;
> + if (metasize)
> + skb_metadata_set(skb, metasize);
> +
> + if (unlikely(xdp_buff_has_frags(xdp)))
> + xdp_update_skb_shared_info(skb, nr_frags,
> + sinfo->xdp_frags_size,
> + xdp_frags_truesz,
> + xdp_buff_is_frag_pfmemalloc(xdp));
> +
> + return skb;
> +}
> +
> /* TODO: build xdp in big mode */
> static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> struct virtnet_info *vi,