netdev - Re: [PATCH bpf-next 2/7] bpf/flow

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Message-ID: <CAPhsuW4rB3ZBrkCwo5yMHdSNNoE8qwho-5iTqR2cnN6HF76iEA@mail.gmail.com>
Date:   Wed, 24 Jul 2019 15:24:29 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [PATCH bpf-next 2/7] bpf/flow_dissector: document flags

On Wed, Jul 24, 2019 at 10:11 AM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> Describe what each input flag does and who uses it.
>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Petar Penkov <ppenkov@...gle.com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  Documentation/bpf/prog_flow_dissector.rst | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/Documentation/bpf/prog_flow_dissector.rst b/Documentation/bpf/prog_flow_dissector.rst
> index ed343abe541e..0f3f380b2ce4 100644
> --- a/Documentation/bpf/prog_flow_dissector.rst
> +++ b/Documentation/bpf/prog_flow_dissector.rst
> @@ -26,6 +26,7 @@ and output arguments.
>    * ``nhoff`` - initial offset of the networking header
>    * ``thoff`` - initial offset of the transport header, initialized to nhoff
>    * ``n_proto`` - L3 protocol type, parsed out of L2 header
> +  * ``flags`` - optional flags
>
>  Flow dissector BPF program should fill out the rest of the ``struct
>  bpf_flow_keys`` fields. Input arguments ``nhoff/thoff/n_proto`` should be
> @@ -101,6 +102,23 @@ can be called for both cases and would have to be written carefully to
>  handle both cases.
>
>
> +Flags
> +=====
> +
> +``flow_keys->flags`` might contain optional input flags that work as follows:
> +
> +* ``FLOW_DISSECTOR_F_PARSE_1ST_FRAG`` - tells BPF flow dissector to continue
> +  parsing first fragment; the default expected behavior is that flow dissector
> +  returns as soon as it finds out that the packet is fragmented;
> +  used by ``eth_get_headlen`` to estimate length of all headers for GRO.
> +* ``FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL`` - tells BPF flow dissector to stop
> +  parsing as soon as it reaches IPv6 flow label; used by ``___skb_get_hash``
> +  and ``__skb_get_hash_symmetric`` to get flow hash.
> +* ``FLOW_DISSECTOR_F_STOP_AT_ENCAP`` - tells BPF flow dissector to stop
> +  parsing as soon as it reaches encapsulated headers; used by routing
> +  infrastructure.
> +
> +
>  Reference Implementation
>  ========================
>
> --
> 2.22.0.657.g960e92d24f-goog
>