netdev - Re: [PATCH bpf-next V4 2/5] bpf: bpf_fib_lookup return MTU value as output when looked up

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Message-ID: <20201030180102.567d3751@carbon>
Date:   Fri, 30 Oct 2020 18:01:02 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     bpf@...r.kernel.org, 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,
        brouer@...hat.com
Subject: Re: [PATCH bpf-next V4 2/5] bpf: bpf_fib_lookup return MTU value as
 output when looked up

On Tue, 27 Oct 2020 11:15:31 -0600
David Ahern <dsahern@...il.com> wrote:

> On 10/27/20 10:26 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@...nel.org>

Thanks a lot for the review.  I didn't propagate-it-over in V5 of this
patch, as I changed the name of the output member from mtu to
mtu_result in V5.  Please review V5 and give your review consent.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer