netdev - Re: [PATCH bpf-next v2 2/9] tools: bpftool: install libbpf headers instead of including the dir

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Date:   Fri, 1 Oct 2021 15:55:41 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 2/9] tools: bpftool: install libbpf headers
 instead of including the dir

On Fri, Oct 1, 2021 at 4:09 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> Bpftool relies on libbpf, therefore it relies on a number of headers
> from the library and must be linked against the library. The Makefile
> for bpftool exposes these objects by adding tools/lib as an include
> directory ("-I$(srctree)/tools/lib"). This is a working solution, but
> this is not the cleanest one. The risk is to involuntarily include
> objects that are not intended to be exposed by the libbpf.
>
> The headers needed to compile bpftool should in fact be "installed" from
> libbpf, with its "install_headers" Makefile target. In addition, there
> is one header which is internal to the library and not supposed to be
> used by external applications, but that bpftool uses anyway.
>
> Adjust the Makefile in order to install the header files properly before
> compiling bpftool. Also copy the additional internal header file
> (nlattr.h), but call it out explicitly. Build (and install headers) in a
> subdirectory under bpftool/ instead of tools/lib/bpf/. When descending
> from a parent Makefile, this is configurable by setting the OUTPUT,
> LIBBPF_OUTPUT and LIBBPF_DESTDIR variables.
>
> Also adjust the Makefile for BPF selftests, so as to reuse the (host)
> libbpf compiled earlier and to avoid compiling a separate version of the
> library just for bpftool.
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  tools/bpf/bpftool/Makefile           | 27 ++++++++++++++++-----------
>  tools/testing/selftests/bpf/Makefile |  2 ++
>  2 files changed, 18 insertions(+), 11 deletions(-)
>

Looks good, but with Makefile no one can ever be sure :) Let's see how
this works in practice...

Acked-by: Andrii Nakryiko <andrii@...nel.org>

> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 1fcf5b01a193..78e42963535a 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -17,16 +17,16 @@ endif
>  BPF_DIR = $(srctree)/tools/lib/bpf/

[...]

> +# We need to copy nlattr.h which is not otherwise exported by libbpf, but still
> +# required by bpftool.
>  $(LIBBPF): FORCE | $(LIBBPF_OUTPUT)
> -       $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) $(LIBBPF_OUTPUT)libbpf.a
> +       $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) \
> +               DESTDIR=$(LIBBPF_DESTDIR) prefix= \
> +               $(LIBBPF_OUTPUT)libbpf.a install_headers

s/$(LIBBPF_OUTPUT)libbpf.a/$(LIBBPF)/ ?

> +       $(call QUIET_INSTALL, bpf/nlattr.h)
> +       $(Q)install -m 644 -t $(LIBBPF_INCLUDE)/bpf/ $(BPF_DIR)nlattr.h
>
>  $(LIBBPF_BOOTSTRAP): FORCE | $(LIBBPF_BOOTSTRAP_OUTPUT)
>         $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) \

[...]