netdev - Re: [PATCH bpf-next 3/3] libbpf: auto-generate list of BPF helper definitions

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Date:   Sat, 5 Oct 2019 19:29:43 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...com>
Cc:     Andrii Nakryiko <andriin@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [PATCH bpf-next 3/3] libbpf: auto-generate list of BPF helper definitions

On Sat, Oct 5, 2019 at 6:01 PM Alexei Starovoitov <ast@...com> wrote:
>
> On 10/5/19 11:24 AM, Andrii Nakryiko wrote:
> > On Sat, Oct 5, 2019 at 10:10 AM Alexei Starovoitov <ast@...com> wrote:
> >>
> >> On 10/5/19 12:59 AM, Andrii Nakryiko wrote:
> >>> Get rid of list of BPF helpers in bpf_helpers.h (irony...) and
> >>> auto-generate it into bpf_helpers_defs.h, which is now included from
> >>> bpf_helpers.h.
> >>>
> >>> Suggested-by: Alexei Starovoitov<ast@...com>
> >>> Signed-off-by: Andrii Nakryiko<andriin@...com>
> >>> ---
> >>>    tools/lib/bpf/Makefile           |    8 +-
> >>>    tools/lib/bpf/bpf_helpers.h      |  264 +--
> >>>    tools/lib/bpf/bpf_helpers_defs.h | 2677 ++++++++++++++++++++++++++++++
> >>>    3 files changed, 2685 insertions(+), 264 deletions(-)
> >>>    create mode 100644 tools/lib/bpf/bpf_helpers_defs.h
> >>
> >> Approach looks good to me.
> >> imo that's better than messing with macros.
> >>
> >> Using bpf_helpers_doc.py as part of build will help man pages too.
> >> I think we were sloppy documenting helpers, since only Quentin
> >> was running that script regularly.
> >
> > Yep, I agree, I had to fix few things, as well as (char *) vs (void *)
> > vs (__u8 *) differences were causing some extra warnings.
> > Please check the list of type translations whether they make sense.
>
> yes. These conversions make sense.

cool, thanks for checking!

> Only one sk_buff->__sk_buff won't work for too long.
> Once my btf vmlinux stuff lands both structs will be possible.

I guess it will have to be sk_buff -> void conversion then, but we'll
do it later.

>
> >>
> >> Only question is what is the reason to commit generated .h into git?
> >
> > So originally I didn't want to depend on system UAPI headers during
> > Github build. But now I recalled that we do have latest UAPI synced
> > into Github's include/ subdir, so that's not an obstacle really. We'll
> > just need to re-license bpf_helpers_doc.py (I don't think Quentin will
> > mind) and start syncing it to Github (not a big deal at all).
>
> github sync script can run make, grab generated .h,
> and check it in into github.

Haven't considered that. That will work as well, a bit more work for
me on sync script side, but that's ok.

>
> >
> > There is still a benefit in having it checked in: easy to spot if
> > script does something wrong and double-check the changes (after
> > initial big commit, of course).
> >
> > If you think that's not reason enough, let me know and I can drop it in v2.
>
> I don't remember too many cases when generated files were committed.
> My preference to keep it out of kernel git.
> github/libbpf is a pure mirror. That .h can be committed there.
> The whole thing is automatic, so we don't need to move .py
> into github too.
>

Yeah, makes sense, will submit v2 w/ bpf_helpers_defs.h added to .gitignore