#ifndef __BPF_CORE_READ_H__
#define __BPF_CORE_READ_H__
+/*
+ * enum bpf_field_info_kind is passed as a second argument into
+ * __builtin_preserve_field_info() built-in to get a specific aspect of
+ * a field, captured as a first argument. __builtin_preserve_field_info(field,
+ * info_kind) returns __u32 integer and produces BTF field relocation, which
+ * is understood and processed by libbpf during BPF object loading. See
+ * selftests/bpf for examples.
+ */
+enum bpf_field_info_kind {
+ BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
+ BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
+};
+
+/*
+ * Convenience macro to check that field actually exists in target kernel's.
+ * Returns:
+ * 1, if matching field is present in target kernel;
+ * 0, if no matching field found.
+ */
+#define bpf_core_field_exists(field) \
+ __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
+
/*
* bpf_core_read() abstracts away bpf_probe_read() call and captures offset
* relocation for source address using __builtin_preserve_access_index()
* a relocation, which records BTF type ID describing root struct/union and an
* accessor string which describes exact embedded field that was used to take
* an address. See detailed description of this relocation format and
- * semantics in comments to struct bpf_offset_reloc in libbpf_internal.h.
+ * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
*
* This relocation allows libbpf to adjust BPF instruction to use correct
* actual field offset, based on target kernel BTF type that matches original