Re: Using AF_XDP To Modify Outgoing Packets

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Tue, 31 Mar 2020 18:22:53 -0500
Christian Deacon <gamemann@gflclan.com> wrote:

> After looking into the TC Hook, it looks like this will work for my 
> case. I'll try to get a program made in the next few days or so.

If you want code examples of TC egress hook with BPF look at[1]:
 [1] https://github.com/xdp-project/xdp-cpumap-tc/

Notice that map pinning with libbpf have gotten easier (thanks to
Toke). This example does work (runs in production), it shares and reuse
maps between XDP and TC-bpf.  The example uses the old way to define
maps, and I recommend switching to the new BTF-based syntax instead
(requires LLVM 10), which defines ".maps" SEC, see example[2], and
notice "pinning" option, which obsoletes a lot of the map code in[1].

Attaching TC-bpf progs are different that XDP.  I've hidden the detail
in C-code function tc_egress_attach_bpf() (see[3]), which actually just
calls the "tc" command.  I was hoping that this would be replaced with a
libbpf call, like we have for XDP, but that have not happened.


[2] https://github.com/xdp-project/xdp-tools/blob/master/xdp-filter/xdpfilt_prog.h#L124-L131
[3] https://github.com/xdp-project/xdp-cpumap-tc/blob/master/src/common_user.c#L386
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

google keywords: tc qdisc clsact cls_bpf egress filter