Merge branch 'selftests-bpf-use-local-types-for-kfunc-declarations'

Merge branch 'selftests-bpf-use-local-types-for-kfunc-declarations'

Gregory Bell says:

====================
selftests/bpf: Use local types for kfunc declarations

The xdp_flowtable and test_tunnel_kern selftests were previously
rewritten to compile with CONFIG_NF_FLOW_TABLE=m and CONFIG_NET_FOU=m.
While the compilation issues were resolved, the tests fail at
runtime. In test_tunnel_kern.c, struct bpf_fou_encap___local is
defined with the correct fields but the kfunc declarations still
reference the forward-declared struct bpf_fou_encap. Similarly,
xdp_flowtable.c uses a forward-declared struct flow_offload_tuple_rhash
as the return type for bpf_xdp_flow_lookup(). Clang emits these forward
declarations as BTF FWD types, which fail to resolve against the
module-defined STRUCT types at run time:

libbpf: extern (func ksym) 'bpf_xdp_flow_lookup': func_proto [51] incompatible with nf_flow_table [128640]
libbpf: extern (func ksym) 'bpf_skb_get_fou_encap': func_proto [79] incompatible with fou [135045]

This patch updates both selftests to use ___local type suffixes
for kernel struct type, replacing the forward declarations.

struct flow_offload_tuple_rhash___local is defined without fields
because the test only uses the returned pointer for a null check.
This avoids needing to locally define its nested types,
struct rhash_head and struct flow_offload_tuple.

I understand that fixing selftests for specific config options is
generally not a priority, but since these tests were already
rewritten to support these configs, they should work correctly
with them.

Fixes: d17f9b370df6 ("selftests/bpf: Fix compilation failure when CONFIG_NET_FOU!=y")
Fixes: eeb23b54e447 ("selftests/bpf: fix compilation failure when CONFIG_NF_FLOW_TABLE=m")
Signed-off-by: Gregory Bell <grbell@redhat.com>
change log:
[0] https://lore.kernel.org/all/cover.1776280396.git.grbell@redhat.com/
- Add BPF_NO_KFUNC_PROTOTYPES macro to test_tunnel_kern.c so the test compiles
  when CONFIG_NET_FOU=y. Without it the function prototypes conflict with vmlinux.h
====================

Link: https://patch.msgid.link/20260417154122.2558890-1-grbell@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>