netdev - Re: [PATCH bpf-next 1/2] bpf: Add flag BPF_F_NO_TUNNEL_KEY to bpf_skb_set_tunnel

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Date:   Mon, 19 Dec 2022 22:24:39 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     Christian Ehrig <cehrig@...udflare.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        Joanne Koong <joannelkoong@...il.com>,
        Kui-Feng Lee <kuifeng@...com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Kaixi Fan <fankaixi.li@...edance.com>,
        Shmulik Ladkani <shmulik@...anetworks.com>,
        Paul Chaignon <paul@...valent.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: Add flag BPF_F_NO_TUNNEL_KEY to
 bpf_skb_set_tunnel_key()

On Sun, Dec 18, 2022 at 06:17 AM +01, Christian Ehrig wrote:
> This patch allows to remove TUNNEL_KEY from the tunnel flags bitmap
> when using bpf_skb_set_tunnel_key by providing a BPF_F_NO_TUNNEL_KEY
> flag. On egress, the resulting tunnel header will not contain a tunnel
> key if the protocol and implementation supports it.
>
> At the moment bpf_tunnel_key wants a user to specify a numeric tunnel
> key. This will wrap the inner packet into a tunnel header with the key
> bit and value set accordingly. This is problematic when using a tunnel
> protocol that supports optional tunnel keys and a receiving tunnel
> device that is not expecting packets with the key bit set. The receiver
> won't decapsulate and drop the packet.
>
> RFC 2890 and RFC 2784 GRE tunnels are examples where this flag is
> useful. It allows for generating packets, that can be decapsulated by
> a GRE tunnel device not operating in collect metadata mode or not
> expecting the key bit set.
>
> Signed-off-by: Christian Ehrig <cehrig@...udflare.com>
> ---

Reviewed-by: Jakub Sitnicki <jakub@...udflare.com>