netdev - Re: [PATCH v2 6/9] virtio_net: transmit the multi-buffer xdp

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Date:   Tue, 27 Dec 2022 15:12:07 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v2 6/9] virtio_net: transmit the multi-buffer xdp


在 2022/12/20 22:14, Heng Qi 写道:
> This serves as the basis for XDP_TX and XDP_REDIRECT
> to send a multi-buffer xdp_frame.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 27 ++++++++++++++++++++++-----
>   1 file changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 40bc58fa57f5..9f31bfa7f9a6 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -563,22 +563,39 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   				   struct xdp_frame *xdpf)
>   {
>   	struct virtio_net_hdr_mrg_rxbuf *hdr;
> -	int err;
> +	struct skb_shared_info *shinfo;
> +	u8 nr_frags = 0;
> +	int err, i;
>   
>   	if (unlikely(xdpf->headroom < vi->hdr_len))
>   		return -EOVERFLOW;
>   
> -	/* Make room for virtqueue hdr (also change xdpf->headroom?) */
> +	if (unlikely(xdp_frame_has_frags(xdpf))) {
> +		shinfo = xdp_get_shared_info_from_frame(xdpf);
> +		nr_frags = shinfo->nr_frags;
> +	}
> +
> +	/* Need to adjust this to calculate the correct postion
> +	 * for shinfo of the xdpf.
> +	 */
> +	xdpf->headroom -= vi->hdr_len;


Any reason we need to do this here? (Or if it is, is it only needed for 
multibuffer XDP?)

Other looks good.

Thanks


>   	xdpf->data -= vi->hdr_len;
>   	/* Zero header and leave csum up to XDP layers */
>   	hdr = xdpf->data;
>   	memset(hdr, 0, vi->hdr_len);
>   	xdpf->len   += vi->hdr_len;
>   
> -	sg_init_one(sq->sg, xdpf->data, xdpf->len);
> +	sg_init_table(sq->sg, nr_frags + 1);
> +	sg_set_buf(sq->sg, xdpf->data, xdpf->len);
> +	for (i = 0; i < nr_frags; i++) {
> +		skb_frag_t *frag = &shinfo->frags[i];
> +
> +		sg_set_page(&sq->sg[i + 1], skb_frag_page(frag),
> +			    skb_frag_size(frag), skb_frag_off(frag));
> +	}
>   
> -	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
> -				   GFP_ATOMIC);
> +	err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
> +				   xdp_to_ptr(xdpf), GFP_ATOMIC);
>   	if (unlikely(err))
>   		return -ENOSPC; /* Caller handle free/refcnt */
>