perf header: Add kerneldoc to 'struct perf_file_header'

Some of the values are a little strange so add documentation to
resolve ambiguity.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yanteng Si <siyanteng@loongson.cn>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20240829150154.37929-4-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.h

@@ -61,14 +61,28 @@ struct perf_file_section {
 	u64 size;
 };
 
+/**
+ * struct perf_file_header: Header representation on disk.
+ */
 struct perf_file_header {
+	/** @magic: Holds "PERFILE2". */
 	u64				magic;
+	/** @size: Size of this header - sizeof(struct perf_file_header). */
 	u64				size;
+	/**
+	 * @attr_size: Size of attrs entries - sizeof(struct perf_event_attr) +
+	 * sizeof(struct perf_file_section).
+	 */
 	u64				attr_size;
+	/** @attrs: Offset and size of file section holding attributes. */
 	struct perf_file_section	attrs;
+	/** @data: Offset and size of file section holding regular event data. */
 	struct perf_file_section	data;
-	/* event_types is ignored */
+	/** @event_types: Ignored. */
 	struct perf_file_section	event_types;
+	/**
+	 * @adds_features: Bitmap of features. The features are immediately after the data section.
+	 */
 	DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
 };