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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Tue, 30 Mar 2021 13:39:27 -0700
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Subject: Re: [PATCH bpf-next 3/5] libbpf: add low level TC-BPF API
To:     Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc:     bpf <bpf@vger.kernel.org>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= <toke@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>,
        open list <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>,
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On Sun, Mar 28, 2021 at 1:11 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Sun, Mar 28, 2021 at 10:12:40AM IST, Andrii Nakryiko wrote:
> > Is there some succinct but complete enough documentation/tutorial/etc
> > that I can reasonably read to understand kernel APIs provided by TC
> > (w.r.t. BPF, of course). I'm trying to wrap my head around this and
> > whether API makes sense or not. Please share links, if you have some.
> >
>
> Hi Andrii,
>
> Unfortunately for the kernel API part, I couldn't find any when I was working
> on this. So I had to read the iproute2 tc code (tc_filter.c, f_bpf.c,
> m_action.c, m_bpf.c) and the kernel side bits (cls_api.c, cls_bpf.c, act_api.c,
> act_bpf.c) to grok anything I didn't understand. There's also similar code in
> libnl (lib/route/{act,cls}.c).
>
> Other than that, these resources were useful (perhaps you already went through
> some/all of them):
>
> https://docs.cilium.io/en/latest/bpf/#tc-traffic-control
> https://qmonnet.github.io/whirl-offload/2020/04/11/tc-bpf-direct-action/
> tc(8), and tc-bpf(8) man pages
>
> I hope this is helpful!

Thanks! I'll take a look. Sorry, I'm a bit behind with all the stuff,
trying to catch up.

I was just wondering if it would be more natural instead of having
_dev _block variants and having to specify __u32 ifindex, __u32
parent_id, __u32 protocol, to have some struct specifying TC
"destination"? Maybe not, but I thought I'd bring this up early. So
you'd have just bpf_tc_cls_attach(), and you'd so something like

bpf_tc_cls_attach(prog_fd, TC_DEV(ifindex, parent_id, protocol))

or

bpf_tc_cls_attach(prog_fd, TC_BLOCK(block_idx, protocol))

? Or it's taking it too far?

But even if not, I think detaching can be unified between _dev and
_block, can't it?

>
> --
> Kartikeya