Re: [PATCH] xdp: Remove unused events xdp_redirect_map and xdp_redirect_map_err

[Jesper Dangaard Brouer]

On 12/06/2025 12.54, Jesper Dangaard Brouer wrote:
> On 12/06/2025 12.30, Toke Høiland-Jørgensen wrote:
> > Steven Rostedt <rostedt@xxxxxxxxxxx> writes:
> >
> > > From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > >
> > > Each TRACE_EVENT() defined can take up around 5K of text and meta data
> > > regardless if they are used or not. New code is being developed that 
> > > will
> > > warn when a tracepoint is defined but not used.
> > >
> > > The trace events xdp_redirect_map and xdp_redirect_map_err are 
> > > defined but
> > > not used, but there's also a comment that states these are kept 
> > > around for
> > > backward compatibility. Which is interesting because since they are not
> > > used, any old BPF program that expects them to exist will get incorrect
> > > data (no data) when they use them. It's worse than not working, it's
> > > silently failing.
> > >
> > > Remove them as they will soon cause warnings, or if they really need to
> > > stick around, then code needs to be added to use them.
> > >
> > > Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> >
> > I guess that makes sense; I have no objections to getting rid of them.
> >
> > Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
>
> Make sense.
>
>
> Toke we have to check how XDP-tools handle when these tracepoints 
> disappears.

To Toke, notice that userspace tools expect this tracepoint to be
available will fail as below (for kernel release v6.16):

 $ sudo ./xdp-bench redirect mlx5p1 veth41
  libbpf: prog 'tp_xdp_redirect_map_err': failed to find kernel BTF 
type ID of 'xdp_redirect_map_err': -3
  libbpf: prog 'tp_xdp_redirect_map_err': failed to prepare load 
attributes: -3
  libbpf: prog 'tp_xdp_redirect_map_err': failed to load: -3
  libbpf: failed to load object 'xdp_redirect_basic'
 Failed to attach XDP program: No such process

IMHO this is a userspace problem, that needs to be more flexible and
adapt to this change.

This was changed in kernel v5.6 (Jan 2020) commit 1d233886dd90 ("xdp:
Use bulking for non-map XDP_REDIRECT and consolidate code paths").
So, I'm thinking that xdp-tools could just remove monitoring for these
tracepoints?

--Jesper