netdev - Re: [PATCH v9 bpf-next 01/14] net: skbuff: add data_len field to skb_shared

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Message-ID: <20210629100852.56d995a6@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 29 Jun 2021 10:08:52 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        bpf <bpf@...r.kernel.org>, Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, shayagr@...zon.com,
        "Jubran, Samih" <sameehj@...zon.com>,
        John Fastabend <john.fastabend@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Saeed Mahameed <saeed@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Tirthendu <tirthendu.sarkar@...el.com>
Subject: Re: [PATCH v9 bpf-next 01/14] net: skbuff: add data_len field to
 skb_shared_info

On Tue, 29 Jun 2021 14:44:56 +0200 Lorenzo Bianconi wrote:
> > On Mon, Jun 14, 2021 at 5:50 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:  
> > >
> > > data_len field will be used for paged frame len for xdp_buff/xdp_frame.
> > > This is a preliminary patch to properly support xdp-multibuff
> > >
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > > ---
> > >  include/linux/skbuff.h | 5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > > index dbf820a50a39..332ec56c200d 100644
> > > --- a/include/linux/skbuff.h
> > > +++ b/include/linux/skbuff.h
> > > @@ -522,7 +522,10 @@ struct skb_shared_info {
> > >         struct sk_buff  *frag_list;
> > >         struct skb_shared_hwtstamps hwtstamps;
> > >         unsigned int    gso_type;
> > > -       u32             tskey;
> > > +       union {
> > > +               u32     tskey;
> > > +               u32     data_len;
> > > +       };
> > >  
> > 
> > Rather than use the tskey field why not repurpose the gso_size field?
> > I would think in the XDP paths that the gso fields would be unused
> > since LRO and HW_GRO would be incompatible with XDP anyway.
> 
> ack, I agree. I will fix it in v10.

Why is XDP mb incompatible with LRO? I thought that was one of the use
cases (mentioned by Willem IIRC).