netdev - RE: [PATCH bpf-next] libbpf: stop using feature-detection Makefiles

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Date:   Wed, 03 Feb 2021 13:31:42 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com, daniel@...earbox.net
Cc:     andrii@...nel.org, kernel-team@...com,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: RE: [PATCH bpf-next] libbpf: stop using feature-detection Makefiles

Andrii Nakryiko wrote:
> Libbpf's Makefile relies on Linux tools infrastructure's feature detection
> framework, but libbpf's needs are very modest: it detects the presence of
> libelf and libz, both of which are mandatory. So it doesn't benefit much from
> the framework, but pays significant costs in terms of maintainability and
> debugging experience, when something goes wrong. The other feature detector,
> testing for the presernce of minimal BPF API in system headers is long
> obsolete as well, providing no value.
> 
> So stop using feature detection and just assume the presence of libelf and
> libz during build time. Worst case, user will get a clear and actionable
> linker error, e.g.:
> 
>   /usr/bin/ld: cannot find -lelf
> 
> On the other hand, we completely bypass recurring issues various users
> reported over time with false negatives of feature detection (libelf or libz
> not being detected, while they are actually present in the system).
> 
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> ---
>  tools/lib/bpf/.gitignore |  1 -
>  tools/lib/bpf/Makefile   | 47 ++++------------------------------------
>  2 files changed, 4 insertions(+), 44 deletions(-)

I've also hit these annoying cases at least once or twice.

Acked-by: John Fastabend <john.fastabend@...il.com>