netdev - Re: [PATCH bpf-next v5 2/3] bpf_xdp_redirect_map: Perform map lookup in eBPF helper

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Date:   Mon, 24 Jun 2019 09:41:12 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Toke Høiland-Jørgensen" <toke@...hat.com>
Cc:     netdev@...r.kernel.org,
        "Jesper Dangaard Brouer" <brouer@...hat.com>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "Alexei Starovoitov" <ast@...nel.org>,
        "David Miller" <davem@...emloft.net>
Subject: Re: [PATCH bpf-next v5 2/3] bpf_xdp_redirect_map: Perform map lookup
 in eBPF helper



On 22 Jun 2019, at 19:17, Toke Høiland-Jørgensen wrote:

> From: Toke Høiland-Jørgensen <toke@...hat.com>
>
> The bpf_redirect_map() helper used by XDP programs doesn't return any
> indication of whether it can successfully redirect to the map index it was
> given. Instead, BPF programs have to track this themselves, leading to
> programs using duplicate maps to track which entries are populated in the
> devmap.
>
> This patch fixes this by moving the map lookup into the bpf_redirect_map()
> helper, which makes it possible to return failure to the eBPF program. The
> lower bits of the flags argument is used as the return code, which means
> that existing users who pass a '0' flag argument will get XDP_ABORTED.
>
> With this, a BPF program can check the return code from the helper call and
> react by, for instance, substituting a different redirect. This works for
> any type of map used for redirect.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>