perf cpu_map: Add cpu_map__empty_new function

Adding cpu_map__empty_new interface to create empty cpumap with given
size. The cpumap entries are initialized with -1.

It'll be used for caching cpu_map in following patches.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1445784728-21732-2-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cpumap.c

@@ -203,6 +203,23 @@ struct cpu_map *cpu_map__dummy_new(void)
 	return cpus;
 }
 
+struct cpu_map *cpu_map__empty_new(int nr)
+{
+	struct cpu_map *cpus = malloc(sizeof(*cpus) + sizeof(int) * nr);
+
+	if (cpus != NULL) {
+		int i;
+
+		cpus->nr = nr;
+		for (i = 0; i < nr; i++)
+			cpus->map[i] = -1;
+
+		atomic_set(&cpus->refcnt, 1);
+	}
+
+	return cpus;
+}
+
 static void cpu_map__delete(struct cpu_map *map)
 {
 	if (map) {

tools/perf/util/cpumap.h

@@ -15,6 +15,7 @@ struct cpu_map {
 };
 
 struct cpu_map *cpu_map__new(const char *cpu_list);
+struct cpu_map *cpu_map__empty_new(int nr);
 struct cpu_map *cpu_map__dummy_new(void);
 struct cpu_map *cpu_map__read(FILE *file);
 size_t cpu_map__fprintf(struct cpu_map *map, FILE *fp);