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 [off-list ref] writes:

quoted

On Sun, Mar 28, 2021 at 1:11 AM Kumar Kartikeya Dwivedi
[off-list ref] wrote:

quoted

On Sun, Mar 28, 2021 at 10:12:40AM IST, Andrii Nakryiko wrote:

quoted

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