netdev - Re: [PATCH bpf-next 0/4] bpf: Generate helpers for pinning through bpf object skeleton

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Date:   Mon, 25 Apr 2022 23:45:21 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 0/4] bpf: Generate helpers for pinning through
 bpf object skeleton

On Sat, Apr 23, 2022 at 7:01 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> Currently there're helpers for allowing to open/load/attach BPF object
> through BPF object skeleton. Let's also add helpers for pinning through
> BPF object skeleton. It could simplify BPF userspace code which wants to
> pin the progs into bpffs.
>
> After this change, with command 'bpftool gen skeleton XXX.bpf.o', the
> helpers for pinning BPF prog will be generated in BPF object skeleton.
>
> The new helpers are named with __{pin, unpin}_prog, because it only pins
> bpf progs. If the user also wants to pin bpf maps, he can use
> LIBBPF_PIN_BY_NAME.

API says it's pinning programs, but really it's trying to pin links.
But those links might not even be created for non-auto-attachable
programs, and for others users might or might not set
<skel>.links.<prog_name> links.

There are lots of questions about this new functionality... But the
main one is why do we need it? What does it bring that's hard to do
otherwise?

>
> Yafang Shao (4):
>   libbpf: Define DEFAULT_BPFFS
>   libbpf: Add helpers for pinning bpf prog through bpf object skeleton
>   bpftool: Fix incorrect return in generated detach helper
>   bpftool: Generate helpers for pinning prog through bpf object skeleton
>
>  tools/bpf/bpftool/gen.c     | 18 ++++++++++-
>  tools/lib/bpf/bpf_helpers.h |  2 +-
>  tools/lib/bpf/libbpf.c      | 61 ++++++++++++++++++++++++++++++++++++-
>  tools/lib/bpf/libbpf.h      | 10 ++++--
>  tools/lib/bpf/libbpf.map    |  2 ++
>  5 files changed, 88 insertions(+), 5 deletions(-)
>
> --
> 2.17.1
>