netdev - Re: [RFC bpf-next 4/5] iproute2: Allow compiling against libbpf

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Date:   Thu, 22 Aug 2019 12:43:56 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>, David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        andrii.nakryiko@...il.com
Subject: Re: [RFC bpf-next 4/5] iproute2: Allow compiling against libbpf

Daniel Borkmann <daniel@...earbox.net> writes:

> On 8/20/19 1:47 PM, Toke Høiland-Jørgensen wrote:
>> This adds a configure check for libbpf and renames functions to allow
>> lib/bpf.c to be compiled with it present. This makes it possible to
>> port functionality piecemeal to use libbpf.
>> 
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>>   configure          | 16 ++++++++++++++++
>>   include/bpf_util.h |  6 +++---
>>   ip/ipvrf.c         |  4 ++--
>>   lib/bpf.c          | 33 +++++++++++++++++++--------------
>>   4 files changed, 40 insertions(+), 19 deletions(-)
>> 
>> diff --git a/configure b/configure
>> index 45fcffb6..5a89ee9f 100755
>> --- a/configure
>> +++ b/configure
>> @@ -238,6 +238,19 @@ check_elf()
>>       fi
>>   }
>>   
>> +check_libbpf()
>> +{
>> +    if ${PKG_CONFIG} libbpf --exists; then
>> +	echo "HAVE_LIBBPF:=y" >>$CONFIG
>> +	echo "yes"
>> +
>> +	echo 'CFLAGS += -DHAVE_LIBBPF' `${PKG_CONFIG} libbpf --cflags` >> $CONFIG
>> +	echo 'LDLIBS += ' `${PKG_CONFIG} libbpf --libs` >>$CONFIG
>> +    else
>> +	echo "no"
>> +    fi
>> +}
>> +
>>   check_selinux()
>
> More of an implementation detail at this point in time, but want to
> make sure this doesn't get missed along the way: as discussed at
> bpfconf [0] best for iproute2 to handle libbpf support would be the
> same way of integration as pahole does, that is, to integrate it via
> submodule [1] to allow kernel and libbpf features to be in sync with
> iproute2 releases and therefore easily consume extensions we're adding
> to libbpf to aide iproute2 integration.

I can sorta see the point wrt keeping in sync with kernel features. But
how will this work with distros that package libbpf as a regular
library? Have you guys given up on regular library symbol versioning for
libbpf?

>    [0] http://vger.kernel.org/bpfconf2019.html#session-4

Thanks for that link! Didn't manage to find any of the previous
discussions on iproute2 compatibility.

-Toke