netdev - Re: [PATCH bpf-next 3/5] libbpf: add low level TC-BPF API

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Message-ID: <20210331093026.hbxjbu43dnlm6mr4@apollo>
Date:   Wed, 31 Mar 2021 15:02:29 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>,
        Jesper Dangaard Brouer <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>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/5] libbpf: add low level TC-BPF API

On Wed, Mar 31, 2021 at 02:41:40AM IST, Toke Høiland-Jørgensen wrote:
> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
>
> > On Sun, Mar 28, 2021 at 1:11 AM Kumar Kartikeya Dwivedi
> > <memxor@...il.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?
>
> Hmm, that's not a bad idea, actually. An earlier version of the series
> did have only a single set of functions, but with way too many
> arguments, which is why we ended up agreeing to split them. But
> encapsulating the destination in a separate struct and combining it with
> some helper macros might just make this work! I like it! Kumar, WDYT?
>

SGTM.

> -Toke
>

--
Kartikeya