Re: [PATCHv6 bpf-next 2/3] sample/bpf: add xdp_redirect_map_multicast test

On Fri, Jul 10, 2020 at 12:40:11AM +0200, Daniel Borkmann wrote:

quoted

+SEC("xdp_redirect_map_multi")
+int xdp_redirect_map_multi_prog(struct xdp_md *ctx)
+{
+	long *value;
+	u32 key = 0;
+
+	/* count packet in global counter */
+	value = bpf_map_lookup_elem(&rxcnt, &key);
+	if (value)
+		*value += 1;
+
+	return bpf_redirect_map_multi(&forward_map, &null_map,
+				      BPF_F_EXCLUDE_INGRESS);

Why not extending to allow use-case like ...

  return bpf_redirect_map_multi(&fwd_map, NULL, BPF_F_EXCLUDE_INGRESS);

... instead of requiring a dummy/'null' map?

I planed to let user set NULL, but the arg2_type is ARG_CONST_MAP_PTR, which
not allow NULL pointer.

Thanks
Hangbin