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

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Date:   Wed, 27 Apr 2022 00:09:22 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...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 Tue, Apr 26, 2022 at 2:45 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> 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.

Actually it should be bpf_object__pin_skeleton_link().

> 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?
>

See also my replyment to Daniel[1].
For the FD-based bpf objects, the userspace code is similar, so we can
abstract the userspace code into a common code, and then the developer
doesn't need to write the userspace code any more (if he doesn't have
some special userspace logical.).


[1]. https://lore.kernel.org/bpf/CAEf4BzbhODOBrE=unLOUpo40uUYz72BJX-+uJobiwhF9VFSizQ@mail.gmail.com/T/#m32dfc6343f2b4fba980c62686b245cb6e0133c2f


> >
> > 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
> >



-- 
Regards
Yafang