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

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

On 4/28/21 12:36 AM, Toke Høiland-Jørgensen wrote:
> Daniel Borkmann <daniel@xxxxxxxxxxxxx> 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