netdev - Re: [PATCH bpf-next V3 2/6] bpf: bpf_fib_lookup return MTU value as output when looked up

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Date:   Thu, 8 Oct 2020 21:05:44 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        maze@...gle.com, lmb@...udflare.com, shaun@...era.io,
        Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, eyal.birger@...il.com
Subject: Re: [PATCH bpf-next V3 2/6] bpf: bpf_fib_lookup return MTU value as
 output when looked up

On 10/8/20 7:09 AM, Jesper Dangaard Brouer wrote:
> The BPF-helpers for FIB lookup (bpf_xdp_fib_lookup and bpf_skb_fib_lookup)
> can perform MTU check and return BPF_FIB_LKUP_RET_FRAG_NEEDED.  The BPF-prog
> don't know the MTU value that caused this rejection.
> 
> If the BPF-prog wants to implement PMTU (Path MTU Discovery) (rfc1191) it
> need to know this MTU value for the ICMP packet.
> 
> Patch change lookup and result struct bpf_fib_lookup, to contain this MTU
> value as output via a union with 'tot_len' as this is the value used for
> the MTU lookup.
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>  include/uapi/linux/bpf.h       |   11 +++++++++--
>  net/core/filter.c              |   17 ++++++++++++-----
>  tools/include/uapi/linux/bpf.h |   11 +++++++++--
>  3 files changed, 30 insertions(+), 9 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@...il.com>