perf diff: Introduce fmt_to_data_file() helper

The fmt_to_data_file() is to retrieve struct data__file from
perf_hpp_fmt which is embedded in diff_hpp_fmt.  It'll be used by sort
callback functions later.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1420677949-6719-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-diff.c

@@ -390,6 +390,15 @@ static void perf_evlist__collapse_resort(struct perf_evlist *evlist)
 	}
 }
 
+static struct data__file *fmt_to_data_file(struct perf_hpp_fmt *fmt)
+{
+	struct diff_hpp_fmt *dfmt = container_of(fmt, struct diff_hpp_fmt, fmt);
+	void *ptr = dfmt - dfmt->idx;
+	struct data__file *d = container_of(ptr, struct data__file, fmt);
+
+	return d;
+}
+
 static struct hist_entry*
 get_pair_data(struct hist_entry *he, struct data__file *d)
 {
@@ -407,8 +416,7 @@ get_pair_data(struct hist_entry *he, struct data__file *d)
 static struct hist_entry*
 get_pair_fmt(struct hist_entry *he, struct diff_hpp_fmt *dfmt)
 {
-	void *ptr = dfmt - dfmt->idx;
-	struct data__file *d = container_of(ptr, struct data__file, fmt);
+	struct data__file *d = fmt_to_data_file(&dfmt->fmt);
 
 	return get_pair_data(he, d);
 }