Re: [PATCH] libbpf: export inline helpers as symbols for xsk

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>, "Björn Töpel" <bjorn@kernel.org>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH] libbpf: export inline helpers as symbols for xsk
Date: Mon, 26 Apr 2021 16:20:04 -0700	[thread overview]
Message-ID: <CAEf4BzaDbVpLvbOnkTKtzHVGq74TfBprLuZ6fJtYqJ+jFZN+Gw@mail.gmail.com> (raw)
In-Reply-To: <20210426202240.518961-1-memxor@gmail.com>

On Mon, Apr 26, 2021 at 1:22 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> This helps people writing language bindings to not have to rewrite C
> wrappers for inline functions in the headers. We force inline the
> definition from the header for C and C++ consumers, but also export a
> symbol in the library for others. This keeps the performance
> advantages similar to using static inline, while also allowing tools
> like Rust's bindgen to generate wrappers for the functions.
>
> Also see
> https://lore.kernel.org/bpf/CAJ8uoz0QqR97qEYYK=VVCE9A=V=k2tKnH6wNM48jeak2RAmL0A@mail.gmail.com/
> for some context.
>
> Also see https://github.com/xdp-project/xdp-tools/pull/97 for more
> discussion on the same.
>
> extern inline is used as it's slightly better since it warns when an
> inline definition is missing.
>
> The fvisibility attribute goes on the inline definition, as essentially
> it acts as a declaration for the function, while the extern inline
> declaration ends up acting as a definition.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

xsk is moving into libxdp, why not do this there, instead of exporting
a lot of symbols that we'll be deprecating very soon. It will also
incentivise customers to make a move more promptly.

Bjorn, Magnus, what's the status of libxsk in libxdp?

>  tools/lib/bpf/libbpf.map | 16 ++++++++++++++
>  tools/lib/bpf/xsk.c      | 24 +++++++++++++++++++++
>  tools/lib/bpf/xsk.h      | 45 +++++++++++++++++++++++-----------------
>  3 files changed, 66 insertions(+), 19 deletions(-)
>

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