netdev - Re: [RFC bpf-next v2 1/9] net: introduce __init_skb{,_data,

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Date:   Thu, 21 Mar 2019 13:56:40 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Stanislav Fomichev <sdf@...ichev.me>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Simon Horman <simon.horman@...ronome.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <peterpenkov96@...il.com>
Subject: Re: [RFC bpf-next v2 1/9] net: introduce __init_skb{,_data,_shinfo} helpers

On Thu, Mar 21, 2019 at 9:13 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> On Thu, Mar 21, 2019 at 12:01 PM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Thu, Mar 21, 2019 at 08:44:33AM -0700, Stanislav Fomichev wrote:
> > >
> > > If we can agree that we switch everything to xpd-like, do we deprecate the
> > > skb-one?
> >
> > This whole discussion that have been going on for long time is an indication
> > that initial bpf flow dissector concept was not thought through
> > and I regret on merging it in the first place.
> > Adding more hacks on top of it with fake skbs is not going to make it any better.
> > Since it's been in the official release we cannot remove it now.
>
> This patch set addresses the only open issue.
>
> That said, if direction is towards an alternative interface, then it would
> make sense for the new interface to supplant the existing one for all
> use-cases, even if that existing one cannot be removed.
>
> Essentially a BPF_PROG_TYPE_FLOW_DISSECTOR_RAW that
> takes a simpler context than skb. And either that or a program of
> type BPF_PROG_TYPE_FLOW_DISSECTOR can be attached in
> skb_flow_dissector_bpf_prog_attach, but not both.

another idea is to keep 'struct __sk_buff' as a context,
but have kernel side to be something like struct xdp_buff
and disallow access to fields of __sk_buff depending on
attach_type.
and do different ctx rewrite for __sk_buff->foo
depending on attach_type.