netdev - Re: [PATCH bpf-next 2/3] bpftool: don't append / to the progtype

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Message-ID: <CAKH8qBt3_qpCLjviMr86EixBx+pVG5E4+ZZeHZpwO6G6wnrR+g@mail.gmail.com>
Date:   Tue, 26 Oct 2021 08:46:30 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH bpf-next 2/3] bpftool: don't append / to the progtype

On Mon, Oct 25, 2021 at 9:27 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Mon, Oct 25, 2021 at 8:59 AM Stanislav Fomichev <sdf@...gle.com> wrote:
> >
> > On Fri, Oct 22, 2021 at 10:05 AM John Fastabend
> > <john.fastabend@...il.com> wrote:
> > >
> > > Stanislav Fomichev wrote:
> > > > Otherwise, attaching with bpftool doesn't work with strict section names.
> > > >
> > > > Also, switch to libbpf strict mode to use the latest conventions
> > > > (note, I don't think we have any cli api guarantees?).
> > > >
> > > > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > > > ---
> > > >  tools/bpf/bpftool/main.c |  4 ++++
> > > >  tools/bpf/bpftool/prog.c | 15 +--------------
> > > >  2 files changed, 5 insertions(+), 14 deletions(-)
> > > >
> > > > diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
> > > > index 02eaaf065f65..8223bac1e401 100644
> > > > --- a/tools/bpf/bpftool/main.c
> > > > +++ b/tools/bpf/bpftool/main.c
> > > > @@ -409,6 +409,10 @@ int main(int argc, char **argv)
> > > >       block_mount = false;
> > > >       bin_name = argv[0];
> > > >
> > > > +     ret = libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
> > > > +     if (ret)
> > > > +             p_err("failed to enable libbpf strict mode: %d", ret);
> > > > +
> > >
> > > Would it better to just warn? Seems like this shouldn't be fatal from
> > > bpftool side?
> > >
> > > Also this is a potentially breaking change correct? Programs that _did_
> > > work in the unstrict might suddently fail in the strict mode? If this
> > > is the case whats the versioning plan? We don't want to leak these
> > > type of changes across multiple versions, idealy we have a hard
> > > break and bump the version.
> > >
> > > I didn't catch a cover letter on the series. A small
> > > note about versioning and upgrading bpftool would be helpful.
> >
> > Yeah, it is a breaking change, every program that has non-strict
> > section names will be rejected.
> >
> > I mentioned that in the bpftool's commit description:
> > Also, switch to libbpf strict mode to use the latest conventions
> > (note, I don't think we have any cli api guarantees?).
> >
> > So I'm actually not sure what's the best way to handle this migration
> > and whether we really provide any cli guarantees to the users. I was
> > always assuming that bpftool is mostly for debugging/introspection,
> > but not sure.
> >
> > As Andrii suggested in another email, I can add a flag to disable this
> > strict mode. Any better ideas?
>
> Maybe the other way around for the transition period. Add a --strict
> flag to turn on libbpf strict mode? This follows libbpf's opt-in
> approach to breaking change. We can also emit warnings when people are
> trying to pin programs and mention that they should switch to --strict
> as in some future version this will be the default. Would that be
> better for users?

Agreed, that sounds better for backwards compatibility. However, I'm
not sure when we set that --strict to 'true' by default. The same
moment libbpf loses non-strict behavior?