netdev - Re: [PATCH bpf-next 5/5] libbpf: add selftests for TC-BPF API

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Date:   Sat, 27 Mar 2021 16:17:16 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf@...r.kernel.org, brouer@...hat.com,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next 5/5] libbpf: add selftests for TC-BPF API

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> On Thu, Mar 25, 2021 at 05:30:03PM +0530, Kumar Kartikeya Dwivedi wrote:
>> This adds some basic tests for the low level bpf_tc_* API and its
>> bpf_program__attach_tc_* wrapper on top.
>
> *_block() apis from patch 3 and 4 are not covered by this selftest.
> Why were they added ? And how were they tested?
>
> Pls trim your cc. bpf@...r and netdev@...r would have been enough.
>
> My main concern with this set is that it adds netlink apis to libbpf while
> we already agreed to split xdp manipulation pieces out of libbpf.
> It would be odd to add tc apis now only to split them later.

We're not removing the ability to attach an XDP program via netlink from
libxdp, though. This is the equivalent for TC: the minimum support to
attach a program, and if you want to do more, you pull in another
library or roll your own.

I'm fine with cutting out more stuff and making this even more minimal
(e.g., remove the block stuff and only support attach/detach on ifaces),
but we figured we'd err on the side of including too much and getting
some feedback from others on which bits are the essential ones to keep,
and which can be dropped.

> I think it's better to start with new library for tc/xdp and have
> libbpf as a dependency on that new lib.
> For example we can add it as subdir in tools/lib/bpf/.

I agree for the higher-level stuff (though I'm not sure what that would
be for TC), but right now TC programs are the only ones that cannot be
attached by libbpf, which is annoying; that's what we're trying to fix.

-Toke