Re: [RFC PATCH 5/9] virtio_net: build xdp_buff with multi buffers

Jason Wang
2022-12-06T06:15:21Z

On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@linux.alibaba.com> wrote:
>
> Support xdp for multi buffer packets.
>
> Putting the first buffer as the linear part for xdp_buff,
> and the rest of the buffers as non-linear fragments to struct
> skb_shared_info in the tailroom belonging to xdp_buff.
>
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 74 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index cd65f85d5075..20784b1d8236 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -911,6 +911,80 @@ static struct sk_buff *receive_big(struct net_device *dev,
> return NULL;
> }
>
> +static int virtnet_build_xdp_buff(struct net_device *dev,
> + struct virtnet_info *vi,
> + struct receive_queue *rq,
> + struct xdp_buff *xdp,
> + void *buf,
> + unsigned int len,
> + unsigned int frame_sz,
> + u16 *num_buf,
> + unsigned int *xdp_frags_truesize,
> + struct virtnet_rq_stats *stats)
> +{
> + unsigned int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> + struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> + unsigned int truesize, headroom;
> + struct skb_shared_info *shinfo;
> + unsigned int xdp_frags_truesz = 0;
> + unsigned int cur_frag_size;
> + struct page *page;
> + skb_frag_t *frag;
> + int offset;
> + void *ctx;
> +
> + xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
> + xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
> + VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
> + shinfo = xdp_get_shared_info_from_buff(xdp);
> + shinfo->nr_frags = 0;
> + shinfo->xdp_frags_size = 0;
> +
> + if ((*num_buf - 1) > MAX_SKB_FRAGS)
> + return -EINVAL;
> +
> + while ((--*num_buf) >= 1) {
> + buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);

So this works only for a mergeable buffer, I wonder if it's worth it
to make it work for big mode as well. Or at least we can mention it as
a TODO somewhere and rename this function (with mergeable suffix).

Others look good.

Thanks

> + if (unlikely(!buf)) {
> + pr_debug("%s: rx error: %d buffers out of %d missing\n",
> + dev->name, *num_buf,
> + virtio16_to_cpu(vi->vdev, hdr->num_buffers));
> + dev->stats.rx_length_errors++;
> + return -EINVAL;
> + }
> +
> + if (!xdp_buff_has_frags(xdp))
> + xdp_buff_set_frags_flag(xdp);
> +
> + stats->bytes += len;
> + page = virt_to_head_page(buf);
> + offset = buf - page_address(page);
> + truesize = mergeable_ctx_to_truesize(ctx);
> + headroom = mergeable_ctx_to_headroom(ctx);
> +
> + cur_frag_size = truesize + (headroom ? (headroom + tailroom) : 0);
> + xdp_frags_truesz += cur_frag_size;
> + if (unlikely(len > truesize || cur_frag_size > PAGE_SIZE)) {
> + pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> + dev->name, len, (unsigned long)ctx);
> + dev->stats.rx_length_errors++;
> + return -EINVAL;
> + }
> +
> + frag = &shinfo->frags[shinfo->nr_frags++];
> + __skb_frag_set_page(frag, page);
> + skb_frag_off_set(frag, offset);
> + skb_frag_size_set(frag, len);
> + if (page_is_pfmemalloc(page))
> + xdp_buff_set_frag_pfmemalloc(xdp);
> +
> + shinfo->xdp_frags_size += len;
> + }
> +
> + *xdp_frags_truesize = xdp_frags_truesz;
> + return 0;
> +}
> +
> static struct sk_buff *receive_mergeable(struct net_device *dev,
> struct virtnet_info *vi,
> struct receive_queue *rq,
> --
> 2.19.1.6.gb485710b
>