netdev - Re: [RFC bpf-next v2 7/9] bpf: when doing BPF_PROG_TEST

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Date:   Tue, 19 Mar 2019 22:14:43 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Network Development <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        simon.horman@...ronome.com, Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <peterpenkov96@...il.com>
Subject: Re: [RFC bpf-next v2 7/9] bpf: when doing BPF_PROG_TEST_RUN for flow
 dissector use no-skb mode

On Tue, Mar 19, 2019 at 6:21 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> Now that we have __flow_bpf_dissect which works on raw data (by
> constructing temporary on-stack skb), use it when doing
> BPF_PROG_TEST_RUN for flow dissector.
>
> This should help us catch any possible bugs due to missing shinfo on
> the per-cpu skb.
>
> Note that existing __skb_flow_bpf_dissect swallows L2 headers and returns
> nhoff=0, we need to preserve the existing behavior.
>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  net/bpf/test_run.c | 48 ++++++++++++++--------------------------------
>  1 file changed, 14 insertions(+), 34 deletions(-)
>

> @@ -300,9 +277,13 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
>         preempt_disable();
>         time_start = ktime_get_ns();
>         for (i = 0; i < repeat; i++) {
> -               retval = bpf_flow_dissect_skb(prog, skb,
> -                                             &flow_keys_dissector,
> -                                             &flow_keys);
> +               retval = bpf_flow_dissect(prog, data, eth->h_proto, ETH_HLEN,
> +                                         size, &flow_keys_dissector,
> +                                         &flow_keys);
> +               if (flow_keys.nhoff >= ETH_HLEN)
> +                       flow_keys.nhoff -= ETH_HLEN;
> +               if (flow_keys.thoff >= ETH_HLEN)
> +                       flow_keys.thoff -= ETH_HLEN;

why are these conditional?