Re: [RFC PATCH 4/9] virtio_net: remove xdp related info from page_to_skb()

[Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>]

在 2022/12/6 下午1:36, Jason Wang 写道:
> On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>
> > Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> 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()

Your comments are informative, I'm going to make this patch more 
independent of
"[PATCH 9/9] virtio_net: support multi-buffer xdp", so that each patch 
doesn't break anything.

Thanks.

> 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