netdev - Re: [PATCH bpf-next 09/13] bpf: add bpf_skb_adjust

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Date:   Thu, 21 Mar 2019 09:25:05 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next 09/13] bpf: add bpf_skb_adjust_room encap flags

On Wed, Mar 20, 2019 at 11:13 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Wed, Mar 20, 2019 at 10:49:40AM -0400, Willem de Bruijn wrote:
> > From: Willem de Bruijn <willemb@...gle.com>
> >
> > When pushing tunnel headers, annotate skbs in the same way as tunnel
> > devices.
> >
> > For GSO packets, the network stack requires certain fields set to
> > segment packets with tunnel headers. gro_gse_segment depends on
> > transport and inner mac header, for instance.
> >
> > Add an option to pass this information.
> >
> > Remove the restriction on len_diff to network header length, which
> > is too short, e.g., for GRE protocols.
> >
> > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> > ---
> >  include/uapi/linux/bpf.h | 14 +++++++++-
> >  net/core/filter.c        | 58 +++++++++++++++++++++++++++++++++++++---
> >  2 files changed, 67 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 0eda8f564a381..a444534cc88d7 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -2595,7 +2595,19 @@ enum bpf_func_id {
> >
> >  /* BPF_FUNC_skb_adjust_room flags. */
> >  #define BPF_F_ADJ_ROOM_FIXED_GSO     (1ULL << 0)
> > -#define BPF_F_ADJ_ROOM_MASK          (BPF_F_ADJ_ROOM_FIXED_GSO)
> > +
> > +#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 (1ULL << 1)
> > +#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV6 (1ULL << 2)
> > +#define BPF_F_ADJ_ROOM_ENCAP_L3_MASK (BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 | \
> > +                                      BPF_F_ADJ_ROOM_ENCAP_L3_IPV6)
> > +
> > +#define BPF_F_ADJ_ROOM_ENCAP_L4_GRE  (1ULL << 3)
> > +#define BPF_F_ADJ_ROOM_ENCAP_L4_UDP  (1ULL << 4)
> > +
> > +#define BPF_F_ADJ_ROOM_MASK          (BPF_F_ADJ_ROOM_FIXED_GSO | \
> > +                                      BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \
> > +                                      BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \
> > +                                      BPF_F_ADJ_ROOM_ENCAP_L4_UDP)
>
> The patches looks great.
> One small nit. Please move *_MASK out of uapi.
> When flags are added this uapi macro keeps changing
> which may break user space compiled with older macro.

Ah, good point. Thanks, Alexei. Will fix in v2.


> Essentially user space cannot rely on this macro and cannot use it.
> I think it's best to leave this macro for kernel internals.