[PATCH 1/3] selftests/hid: ensure we can compile the tests on kernels pre-6.3

[Benjamin Tissoires <bentiss@kernel.org>]

For the hid-bpf tests to compile, we need to have the definition of
struct hid_bpf_ctx. This definition is an internal one from the kernel
and it is supposed to be defined in the generated vmlinux.h.

This vmlinux.h header is generated based on the currently running kernel
or if the kernel was already compiled in the tree. If you just compile
the selftests without compiling the kernel beforehand and you are running
on a 6.2 kernel, you'll end up with a vmlinux.h without the hid_bpf_ctx
definition.

Use the clever trick from tools/testing/selftests/bpf/progs/bpf_iter.h
to force the definition of that symbol in case we don't find it in the
BTF.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 tools/testing/selftests/hid/progs/hid.c             |  3 ---
 tools/testing/selftests/hid/progs/hid_bpf_helpers.h | 20 ++++++++++++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/hid/progs/hid.c b/tools/testing/selftests/hid/progs/hid.c
index 88c593f753b5..1e558826b809 100644
--- a/tools/testing/selftests/hid/progs/hid.c
+++ b/tools/testing/selftests/hid/progs/hid.c
@@ -1,8 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2022 Red hat */
-#include "vmlinux.h"
-#include <bpf/bpf_helpers.h>
-#include <bpf/bpf_tracing.h>
 #include "hid_bpf_helpers.h"
 
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/hid/progs/hid_bpf_helpers.h b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
index 4fff31dbe0e7..749097f8f4d9 100644
--- a/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
+++ b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
@@ -5,6 +5,26 @@
 #ifndef __HID_BPF_HELPERS_H
 #define __HID_BPF_HELPERS_H
 
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define hid_bpf_ctx hid_bpf_ctx___not_used
+#include "vmlinux.h"
+#undef hid_bpf_ctx
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+
+struct hid_bpf_ctx {
+	__u32 index;
+	const struct hid_device *hid;
+	__u32 allocated_size;
+	enum hid_report_type report_type;
+	union {
+		__s32 retval;
+		__s32 size;
+	};
+};
+
 /* following are kfuncs exported by HID for HID-BPF */
 extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
 			      unsigned int offset,

-- 
2.39.1