netdev - Re: [PATCH bpf-next v2 00/10] tools: Use consistent libbpf include paths everywhere

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Message-ID: <20200115211900.h44pvhe57szzzymc@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 15 Jan 2020 13:19:02 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kselftest@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH bpf-next v2 00/10] tools: Use consistent libbpf include
 paths everywhere

On Wed, Jan 15, 2020 at 03:12:48PM +0100, Toke Høiland-Jørgensen wrote:
> The recent commit 6910d7d3867a ("selftests/bpf: Ensure bpf_helper_defs.h are
> taken from selftests dir") broke compilation against libbpf if it is installed
> on the system, and $INCLUDEDIR/bpf is not in the include path.
> 
> Since having the bpf/ subdir of $INCLUDEDIR in the include path has never been a
> requirement for building against libbpf before, this needs to be fixed. One
> option is to just revert the offending commit and figure out a different way to
> achieve what it aims for. However, this series takes a different approach:
> Changing all in-tree users of libbpf to consistently use a bpf/ prefix in
> #include directives for header files from libbpf.

I don't think such approach will work in all cases.
Consider the user installing libbpf headers into /home/somebody/include/bpf/,
passing that path to -I and trying to build bpf progs
that do #include "bpf_helpers.h"...
In the current shape of libbpf everything will compile fine,
but after patch 8 of this series the compiler will not find bpf/bpf_helper_defs.h.
So I think we have no choice, but to revert that part of Andrii's patch.
Note that doing #include "" for additional library headers is a common practice.
There was nothing wrong about #include "bpf_helper_defs.h" in bpf_helpers.h.