netdev - Re: [RFC bpf-next 0/5] Convert iproute2 to use libbpf (WIP)

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Date:   Wed, 21 Aug 2019 23:07:03 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [RFC bpf-next 0/5] Convert iproute2 to use libbpf (WIP)

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> On Tue, Aug 20, 2019 at 4:47 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> iproute2 uses its own bpf loader to load eBPF programs, which has
>> evolved separately from libbpf. Since we are now standardising on
>> libbpf, this becomes a problem as iproute2 is slowly accumulating
>> feature incompatibilities with libbpf-based loaders. In particular,
>> iproute2 has its own (expanded) version of the map definition struct,
>> which makes it difficult to write programs that can be loaded with both
>> custom loaders and iproute2.
>>
>> This series seeks to address this by converting iproute2 to using libbpf
>> for all its bpf needs. This version is an early proof-of-concept RFC, to
>> get some feedback on whether people think this is the right direction.
>>
>> What this series does is the following:
>>
>> - Updates the libbpf map definition struct to match that of iproute2
>>   (patch 1).
>
>
> Hi Toke,
>
> Thanks for taking a stab at unifying libbpf and iproute2 loaders. I'm
> totally in support of making iproute2 use libbpf to load/initialize
> BPF programs. But I'm against adding iproute2-specific fields to
> libbpf's bpf_map_def definitions to support this.
>
> I've proposed the plan of extending libbpf's supported features so
> that it can be used to load iproute2-style BPF programs earlier,
> please see discussions in [0] and [1].

Yeah, I've seen that discussion, and agree that longer term this is
probably a better way to do map-in-map definitions.

However, I view your proposal as complementary to this series: we'll
probably also want the BTF-based definition to work with iproute2, and
that means iproute2 needs to be ported to libbpf. But iproute2 needs to
be backwards compatible with the format it supports now, and, well, this
series is the simplest way to achieve that IMO :)

> I think instead of emulating iproute2 way of matching everything based
> on user-specified internal IDs, which doesn't provide good user
> experience and is quite easy to get wrong, we should support same
> scenarios with better declarative syntax and in a less error-prone
> way. I believe we can do that by relying on BTF more heavily (again,
> please check some of my proposals in [0], [1], and discussion with
> Daniel in those threads). It will feel more natural and be more
> straightforward to follow. It would be great if you can lend a hand in
> implementing pieces of that plan!
>
> I'm currently on vacation, so my availability is very sparse, but I'd
> be happy to discuss this further, if need be.

Happy to collaborate on your proposal when you're back from vacation;
but as I said above, I believe this is a complementary longer-term
thing...

-Toke