Date:   Tue, 6 Dec 2022 13:36:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        "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>
Subject: Re: [RFC PATCH 4/9] virtio_net: remove xdp related info from page_to_skb()

On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
> For the clear construction of multi-buffer xdp_buff, we now remove the xdp
> processing interleaved with page_to_skb() before, and the logic of xdp and
> building skb from xdp will be separate and independent.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>

So I think the organization of this series needs some tweak.

If I was not not and if we do things like this, XDP support is
actually broken and it breaks bisection and a lot of other things.

We need make sure each patch does not break anything, it probably requires

1) squash the following patches or
2) having a new helper to do XDP stuffs after/before page_to_skb()

Thanks

> ---
>  drivers/net/virtio_net.c | 41 +++++++++-------------------------------
>  1 file changed, 9 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index d3e8c63b9c4b..cd65f85d5075 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -439,9 +439,7 @@ static unsigned int mergeable_ctx_to_truesize(void *mrg_ctx)
>  static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>                                    struct receive_queue *rq,
>                                    struct page *page, unsigned int offset,
> -                                  unsigned int len, unsigned int truesize,
> -                                  bool hdr_valid, unsigned int metasize,
> -                                  unsigned int headroom)
> +                                  unsigned int len, unsigned int truesize)
>  {
>         struct sk_buff *skb;
>         struct virtio_net_hdr_mrg_rxbuf *hdr;
> @@ -459,21 +457,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>         else
>                 hdr_padded_len = sizeof(struct padded_vnet_hdr);
>
> -       /* If headroom is not 0, there is an offset between the beginning of the
> -        * data and the allocated space, otherwise the data and the allocated
> -        * space are aligned.
> -        *
> -        * Buffers with headroom use PAGE_SIZE as alloc size, see
> -        * add_recvbuf_mergeable() + get_mergeable_buf_len()
> -        */
> -       truesize = headroom ? PAGE_SIZE : truesize;
> -       tailroom = truesize - headroom;
> -       buf = p - headroom;
> -
> +       buf = p;
>         len -= hdr_len;
>         offset += hdr_padded_len;
>         p += hdr_padded_len;
> -       tailroom -= hdr_padded_len + len;
> +       tailroom = truesize - hdr_padded_len - len;
>
>         shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> @@ -503,7 +491,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>         if (len <= skb_tailroom(skb))
>                 copy = len;
>         else
> -               copy = ETH_HLEN + metasize;
> +               copy = ETH_HLEN;
>         skb_put_data(skb, p, copy);
>
>         len -= copy;
> @@ -542,19 +530,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>                 give_pages(rq, page);
>
>  ok:
> -       /* hdr_valid means no XDP, so we can copy the vnet header */
> -       if (hdr_valid) {
> -               hdr = skb_vnet_hdr(skb);
> -               memcpy(hdr, hdr_p, hdr_len);
> -       }
> +       hdr = skb_vnet_hdr(skb);
> +       memcpy(hdr, hdr_p, hdr_len);
>         if (page_to_free)
>                 put_page(page_to_free);
>
> -       if (metasize) {
> -               __skb_pull(skb, metasize);
> -               skb_metadata_set(skb, metasize);
> -       }
> -
>         return skb;
>  }
>
> @@ -917,7 +897,7 @@ static struct sk_buff *receive_big(struct net_device *dev,
>  {
>         struct page *page = buf;
>         struct sk_buff *skb =
> -               page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0, 0);
> +               page_to_skb(vi, rq, page, 0, len, PAGE_SIZE);
>
>         stats->bytes += len - vi->hdr_len;
>         if (unlikely(!skb))
> @@ -1060,9 +1040,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>                                 rcu_read_unlock();
>                                 put_page(page);
>                                 head_skb = page_to_skb(vi, rq, xdp_page, offset,
> -                                                      len, PAGE_SIZE, false,
> -                                                      metasize,
> -                                                      headroom);
> +                                                      len, PAGE_SIZE);
>                                 return head_skb;
>                         }
>                         break;
> @@ -1116,8 +1094,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>         rcu_read_unlock();
>
>  skip_xdp:
> -       head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
> -                              metasize, headroom);
> +       head_skb = page_to_skb(vi, rq, page, offset, len, truesize);
>         curr_skb = head_skb;
>
>         if (unlikely(!curr_skb))
> --
> 2.19.1.6.gb485710b
>

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