netdev - Re: [PATCH net-next v2 20/33] vhost_net: also populate XDP frame size

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Date:   Wed, 6 May 2020 14:41:04 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, sameehj@...zon.com
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, zorik@...zon.com,
        akiyano@...zon.com, gtzalik@...zon.com,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        David Ahern <dsahern@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        steffen.klassert@...unet.com
Subject: Re: [PATCH net-next v2 20/33] vhost_net: also populate XDP frame size


On 2020/4/30 下午7:22, Jesper Dangaard Brouer wrote:
> In vhost_net_build_xdp() the 'buf' that gets queued via an xdp_buff
> have embedded a struct tun_xdp_hdr (located at xdp->data_hard_start)
> which contains the buffer length 'buflen' (with tailroom for
> skb_shared_info). Also storing this buflen in xdp->frame_sz, does not
> obsolete struct tun_xdp_hdr, as it also contains a struct
> virtio_net_hdr with other information.
>
> Cc: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>   drivers/vhost/net.c |    1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 2927f02cc7e1..516519dcc8ff 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -747,6 +747,7 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>   	xdp->data = buf + pad;
>   	xdp->data_end = xdp->data + len;
>   	hdr->buflen = buflen;
> +	xdp->frame_sz = buflen;
>   
>   	--net->refcnt_bias;
>   	alloc_frag->offset += buflen;


Hi Jesper:

As I said in v1, tun will do this for us (patch 19) via hdr->buflen. So 
it looks to me this is not necessary?

Thanks

>
>