ubuntu_bpf failed to build on Noble

[Po-Hsu Lin]

Test build failed since 6.8.0-19.19 (probably way more earlier, this is earliest one that I can see):

    CLNG-BPF [test_maps] test_tcpnotify_kern.bpf.o
    CLNG-BPF [test_maps] test_time_tai.bpf.o
    CLNG-BPF [test_maps] test_trace_ext.bpf.o
    CLNG-BPF [test_maps] test_trace_ext_tracing.bpf.o
    CLNG-BPF [test_maps] test_tracepoint.bpf.o
    CLNG-BPF [test_maps] test_trampoline_count.bpf.o
    CLNG-BPF [test_maps] test_tunnel_kern.bpf.o
  make[1]: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf'
  make: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests'
  stderr:
  Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'
  Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'
  progs/test_tunnel_kern.c:30:13: error: declaration of 'struct bpf_fou_encap' will not be visible outside of this function [-Werror,-Wvisibility]
     30 | struct bpf_fou_encap *encap, int type) __ksym;
        | ^
  progs/test_tunnel_kern.c:32:13: error: declaration of 'struct bpf_fou_encap' will not be visible outside of this function [-Werror,-Wvisibility]
     32 | struct bpf_fou_encap *encap) __ksym;
        | ^
  progs/test_tunnel_kern.c:741:23: error: variable has incomplete type 'struct bpf_fou_encap'
    741 | struct bpf_fou_encap encap = {};
        | ^
  progs/test_tunnel_kern.c:741:9: note: forward declaration of 'struct bpf_fou_encap'
    741 | struct bpf_fou_encap encap = {};
        | ^
  progs/test_tunnel_kern.c:765:43: error: use of undeclared identifier 'FOU_BPF_ENCAP_GUE'
    765 | ret = bpf_skb_set_fou_encap(skb, &encap, FOU_BPF_ENCAP_GUE);
        | ^
  progs/test_tunnel_kern.c:778:23: error: variable has incomplete type 'struct bpf_fou_encap'
    778 | struct bpf_fou_encap encap = {};
        | ^
  progs/test_tunnel_kern.c:778:9: note: forward declaration of 'struct bpf_fou_encap'
    778 | struct bpf_fou_encap encap = {};
        | ^
  progs/test_tunnel_kern.c:802:43: error: use of undeclared identifier 'FOU_BPF_ENCAP_FOU'
    802 | ret = bpf_skb_set_fou_encap(skb, &encap, FOU_BPF_ENCAP_FOU);
        | ^
  progs/test_tunnel_kern.c:816:23: error: variable has incomplete type 'struct bpf_fou_encap'
    816 | struct bpf_fou_encap encap = {};
        | ^
  progs/test_tunnel_kern.c:816:9: note: forward declaration of 'struct bpf_fou_encap'
    816 | struct bpf_fou_encap encap = {};
        | ^
  7 errors generated.
  make[1]: *** [Makefile:620: /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/test_tunnel_kern.bpf.o] Error 1
  make: *** [Makefile:180: all] Error 2

[Magali Lemes do Sacramento (magalilemes)]

Seems that it needs CONFIG_NET_FOU=y as per https://lore.kernel<email address hidden>/T/#m8b94d7590580d70a87755d1df3c72af7962912eb
and we have CONFIG_NET_FOU=m