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

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Date:   Tue, 04 Feb 2020 09:25:45 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        David Ahern <dsahern@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        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 Mon, Feb 3, 2020 at 8:53 PM David Ahern <dsahern@...il.com> wrote:
>>
>> On 2/3/20 8:41 PM, Andrii Nakryiko wrote:
>> > On Mon, Feb 3, 2020 at 5:46 PM David Ahern <dsahern@...il.com> wrote:
>> >>
>> >> On 2/3/20 5:56 PM, Andrii Nakryiko wrote:
>> >>> Great! Just to disambiguate and make sure we are in agreement, my hope
>> >>> here is that iproute2 can completely delegate to libbpf all the ELF
>> >>>
>> >>
>> >> iproute2 needs to compile and continue working as is when libbpf is not
>> >> available. e.g., add check in configure to define HAVE_LIBBPF and move
>> >> the existing code and move under else branch.
>> >
>> > Wouldn't it be better to statically compile against libbpf in this
>> > case and get rid a lot of BPF-related code and simplify the rest of
>> > it? This can be easily done by using libbpf through submodule, the
>> > same way as BCC and pahole do it.
>> >
>>
>> iproute2 compiles today and runs on older distributions and older
>> distributions with newer kernels. That needs to hold true after the move
>> to libbpf.
>
> And by statically compiling against libbpf, checked out as a
> submodule, that will still hold true, wouldn't it? Or there is some
> complications I'm missing? Libbpf is designed to handle old kernels
> with no problems.

My plan was to use the same configure test I'm using for xdp-tools
(where I in turn copied the structure of the configure script from
iproute2):

https://github.com/xdp-project/xdp-tools/blob/master/configure#L59

This will look for a system libbpf install and compile against it if it
is compatible, and otherwise fall back to a statically linking against a
git submodule.

We'll need to double-check that this will work on everything currently
supported by iproute2, and fix libbpf if there are any issues with that.
Not that I foresee any, but you never know :)

-Toke