netdev - Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

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Date:   Thu, 22 Apr 2021 13:26:48 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Shaun Crampton <shaun@...era.io>
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>, bpf@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        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 v3 2/3] libbpf: add low level TC-BPF API

On 4/22/21 11:47 AM, Shaun Crampton wrote:
>> Nope, just get it from the prog itself.
> 
> Looks like the API returns the prog ID, so from that we can look up the prog
> and then get its tag? If so that meets our needs.  Alternatively, if
> the API allows
> for atomic replacement of a BPF program with another, that'd also work for us.

Both is the case: from prog ID you can already retrieve that same tag, and progs
can be atomically replaced with the current API code.

Exposing the tag in here otherwise feels just odd/wrong from a design PoV, explain
that to a user of this API on /why/ such field is in the tc API when it already
can be retrieved via bpf_prog_get_info_by_fd(), as in, what is so special on this
field in the tc API here (aside from legacy reasons when there was no mentioned
helper [which we don't need to support given it dates way too far back]) ... I
cannot. ;-) Hence lets drop it from there.

Thanks,
Daniel