netdev - Re: [PATCH bpf-next v4 2/3] libbpf: add low level TC-BPF API

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Date:   Wed, 28 Apr 2021 00:40:06 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        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>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 2/3] libbpf: add low level TC-BPF API

On 4/28/21 12:36 AM, Toke Høiland-Jørgensen wrote:
> Daniel Borkmann <daniel@...earbox.net> writes:
[...]
>> Small addendum:
>>
>>       DECLARE_LIBBPF_OPTS(bpf_tc_hook, hook, .ifindex = 42, .which = BPF_TC_INGRESS|BPF_TC_EGRESS);
>>
>>       err = bpf_tc_hook_create(&hook);
>>       [...]
>>
>> ... is also possible, of course, and then both bpf_tc_hook_{create,destroy}() are symmetric.
> 
> It should be allowed, but it wouldn't actually make any difference which
> combination of TC_INGRESS and TC_EGRESS you specify, as long as one of
> them is set, right? I.e., we just attach the clsact qdisc in both
> cases...

Yes, that is correct, for the bpf_tc_hook_create() whether you pass in BPF_TC_INGRESS,
BPF_TC_EGRESS or BPF_TC_INGRESS|BPF_TC_EGRESS, you'll end up creating clsact qdisc in
either of the three cases. Only the bpf_tc_hook_destroy() differs between all of them.

Thanks,
Daniel