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

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>,
	bpf@vger.kernel.org, brouer@redhat.com,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>, Shuah Khan <shuah@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next 5/5] libbpf: add selftests for TC-BPF API
Date: Sun, 28 Mar 2021 18:26:02 -0700	[thread overview]
Message-ID: <20210329012602.4zzysn2ewbarbn3d@ast-mbp> (raw)
In-Reply-To: <87h7kwaao3.fsf@toke.dk>

On Sat, Mar 27, 2021 at 04:17:16PM +0100, Toke Høiland-Jørgensen wrote:
> Alexei Starovoitov <alexei.starovoitov@gmail.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@vger and netdev@vger 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.

This is up to you. I'm trying to understand the motivation for *_block() apis.
I'm not taking a stance for/against them.

> > 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.

Sure. I wasn't saying that there is no place for these APIs in libbpf+.
Just that existing libbpf is already became a kitchen sink of features
that users are not going to use like static linking.
tc-api was a straw that broke the camel's back.
I think we must move static linking and skeleton out of libbpf before
the next release.