netdev - Re: [PATCHv11 bpf-next 2/5] xdp: add a new helper for dev map multicast support

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Message-ID: <87o8mearu5.fsf@toke.dk>
Date:   Thu, 10 Sep 2020 11:44:50 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        David Ahern <dsahern@...il.com>
Cc:     Hangbin Liu <liuhangbin@...il.com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCHv11 bpf-next 2/5] xdp: add a new helper for dev map
 multicast support

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> On Wed, Sep 9, 2020 at 8:30 PM David Ahern <dsahern@...il.com> wrote:
>> >
>> > I think the packets modification (edit dst mac, add vlan tag, etc) should be
>> > done on egress, which rely on David's XDP egress support.
>>
>> agreed. The DEVMAP used for redirect can have programs attached that
>> update the packet headers - assuming you want to update them.
>
> Then you folks have to submit them as one set.
> As-is the programmer cannot achieve correct behavior.

The ability to attach a program to devmaps is already there. See:

fbee97feed9b ("bpf: Add support to attach bpf program to a devmap entry")

But now that you mention it, it does appear that this series is skipping
the hook that will actually run such a program. Didn't realise that was
in the caller of bq_enqueue() and not inside bq_enqueue() itself...

Hangbin, you'll need to add the hook for dev_map_run_prog() before
bq_enqueue(); see the existing dev_map_enqueue() function.

-Toke