From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: David Ahern <dsahern@gmail.com>
Cc: "Toke Høiland-Jørgensen" <toke@redhat.com>,
"Andrii Nakryiko" <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Kernel Team" <kernel-team@fb.com>,
"David Ahern" <dsahern@kernel.org>,
"Stephen Hemminger" <stephen@networkplumber.org>
Subject: Re: [PATCH v2 bpf-next 3/4] libbpf: deprecate legacy BPF map definitions
Date: Mon, 24 Jan 2022 08:21:46 -0800 [thread overview]
Message-ID: <CAEf4BzaiZz3mW97qXX=Ee5nQS=oRk8zOcv7LMw9r-P4w9k5RPA@mail.gmail.com> (raw)
In-Reply-To: <e58aabf9-af55-8eac-1047-b18801141d80@gmail.com>
On Fri, Jan 21, 2022 at 2:04 PM David Ahern <dsahern@gmail.com> wrote:
>
> On 1/21/22 1:43 PM, Toke Høiland-Jørgensen wrote:
> > Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:
> >
> >> On Thu, Jan 20, 2022 at 3:44 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>>
> >>> Andrii Nakryiko <andrii@kernel.org> writes:
> >>>
> >>>> Enact deprecation of legacy BPF map definition in SEC("maps") ([0]). For
> >>>> the definitions themselves introduce LIBBPF_STRICT_MAP_DEFINITIONS flag
> >>>> for libbpf strict mode. If it is set, error out on any struct
> >>>> bpf_map_def-based map definition. If not set, libbpf will print out
> >>>> a warning for each legacy BPF map to raise awareness that it goes
> >>>> away.
> >>>
> >>> We've touched upon this subject before, but I (still) don't think it's a
> >>> good idea to remove this support entirely: It makes it impossible to
> >>> write a loader that can handle both new and old BPF objects.
> >>>
> >>> So discourage the use of the old map definitions, sure, but please don't
> >>> make it completely impossible to load such objects.
> >>
> >> BTF-defined maps have been around for quite a long time now and only
> >> have benefits on top of the bpf_map_def way. The source code
> >> translation is also very straightforward. If someone didn't get around
> >> to update their BPF program in 2 years, I don't think we can do much
> >> about that.
> >>
> >> Maybe instead of trying to please everyone (especially those that
> >> refuse to do anything to their BPF programs), let's work together to
> >> nudge laggards to actually modernize their source code a little bit
> >> and gain some benefits from that along the way?
> >
> > I'm completely fine with nudging people towards the newer features, and
> > I think the compile-time deprecation warning when someone is using the
> > old-style map definitions in their BPF programs is an excellent way to
> > do that.
> >
> > I'm also fine with libbpf *by default* refusing to load programs that
> > use the old-style map definitions, but if the code is removed completely
> > it becomes impossible to write general-purpose loaders that can handle
> > both old and new programs. The obvious example of such a loader is
> > iproute2, the loader in xdp-tools is another.
> >
>
> I agree with Toke's response.
>
> 2 years is a very small amount of time when it comes to OS and kernel
> versions. Many companies base products on enterprise distributions and
> run them for 10+ years. During that time there will be needs to update
> some components - like kernel version or some tool but that is done with
> the least amount of churn possible. Every update has the potential to
> bring in unknown behavior changes. Requiring updates to entire tool
> chains, multiple tool sets and libraries to accommodate some deprecation
> will only hinder being able to update anything.
>
> Further, programs (e.g., debugging as just one example) can and will
> need to be used across many OS and kernel versions.
Which is why all the things that are being deprecated have better
alternatives that work *right now* with libbpf v0.x and will keep
working with v1.x.
next prev parent reply other threads:[~2022-01-24 16:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-20 6:05 [PATCH v2 bpf-next 0/4] libbpf: deprecate legacy BPF map definitions Andrii Nakryiko
2022-01-20 6:05 ` [PATCH v2 bpf-next 1/4] selftests/bpf: fail build on compilation warning Andrii Nakryiko
2022-01-20 6:05 ` [PATCH v2 bpf-next 2/4] selftests/bpf: convert remaining legacy map definitions Andrii Nakryiko
2022-01-20 6:05 ` [PATCH v2 bpf-next 3/4] libbpf: deprecate legacy BPF " Andrii Nakryiko
2022-01-20 11:44 ` Toke Høiland-Jørgensen
2022-01-20 19:13 ` Andrii Nakryiko
2022-01-21 20:43 ` Toke Høiland-Jørgensen
2022-01-21 22:04 ` David Ahern
2022-01-24 16:21 ` Andrii Nakryiko [this message]
2022-01-24 16:15 ` Andrii Nakryiko
2022-01-25 0:27 ` David Ahern
2022-01-25 5:41 ` Andrii Nakryiko
2022-01-25 12:10 ` Toke Høiland-Jørgensen
2022-01-25 20:52 ` John Fastabend
2022-01-25 21:52 ` Toke Høiland-Jørgensen
2022-01-25 22:35 ` John Fastabend
2022-01-26 0:01 ` Andrii Nakryiko
2022-01-26 2:02 ` David Ahern
2022-01-25 23:46 ` Andrii Nakryiko
2022-01-20 6:05 ` [PATCH v2 bpf-next 4/4] docs/bpf: update BPF map definition example Andrii Nakryiko
2022-01-25 20:52 ` [PATCH v2 bpf-next 0/4] libbpf: deprecate legacy BPF map definitions John Fastabend
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