netdev - Re: [bpf-next v3 9/9] samples/bpf: Add example of ipv4 and ipv6 forwarding in XDP

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Message-ID: <20180510092251.2dc1c904@redhat.com>
Date:   Thu, 10 May 2018 09:22:51 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org, borkmann@...earbox.net, ast@...nel.org,
        davem@...emloft.net, shm@...ulusnetworks.com,
        roopa@...ulusnetworks.com, toke@...e.dk, john.fastabend@...il.com,
        brouer@...hat.com, Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [bpf-next v3 9/9] samples/bpf: Add example of ipv4 and ipv6
 forwarding in XDP

On Wed,  9 May 2018 20:34:27 -0700
David Ahern <dsahern@...il.com> wrote:

> Simple example of fast-path forwarding. It has a serious flaw
> in not verifying the egress device index supports XDP forwarding.
> If the egress device does not packets are dropped.
> 
> Take this only as a simple example of fast-path forwarding.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> Acked-by: David S. Miller <davem@...emloft.net>

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>

I agree that sample program have this flaw, but it should not stop this
patchset. We need to find a more reliable way of detecting/verifying
that an egress device supports XDP forwarding, from within the BPF prog.

As this sample program hints, we could do a lookup in the devmap, to
get this info(?)

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