perf evlist: Introduce perf_evlist__new_dummy constructor

For case where all we need is an evlist with just an "dummy" evsel,
like in some 'perf test' entries.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-q52le0pblm2k3ncvyilelr9z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.c

@@ -68,6 +68,18 @@ struct perf_evlist *perf_evlist__new_default(void)
 	return evlist;
 }
 
+struct perf_evlist *perf_evlist__new_dummy(void)
+{
+	struct perf_evlist *evlist = perf_evlist__new();
+
+	if (evlist && perf_evlist__add_dummy(evlist)) {
+		perf_evlist__delete(evlist);
+		evlist = NULL;
+	}
+
+	return evlist;
+}
+
 /**
  * perf_evlist__set_id_pos - set the positions of event ids.
  * @evlist: selected event list
@@ -248,6 +260,22 @@ error:
 	return -ENOMEM;
 }
 
+int perf_evlist__add_dummy(struct perf_evlist *evlist)
+{
+	struct perf_event_attr attr = {
+		.type	= PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_DUMMY,
+		.size	= sizeof(attr), /* to capture ABI version */
+	};
+	struct perf_evsel *evsel = perf_evsel__new(&attr);
+
+	if (evsel == NULL)
+		return -ENOMEM;
+
+	perf_evlist__add(evlist, evsel);
+	return 0;
+}
+
 static int perf_evlist__add_attrs(struct perf_evlist *evlist,
 				  struct perf_event_attr *attrs, size_t nr_attrs)
 {

tools/perf/util/evlist.h

@@ -67,6 +67,7 @@ struct perf_evsel_str_handler {
 
 struct perf_evlist *perf_evlist__new(void);
 struct perf_evlist *perf_evlist__new_default(void);
+struct perf_evlist *perf_evlist__new_dummy(void);
 void perf_evlist__init(struct perf_evlist *evlist, struct cpu_map *cpus,
 		       struct thread_map *threads);
 void perf_evlist__exit(struct perf_evlist *evlist);
@@ -81,6 +82,8 @@ int __perf_evlist__add_default_attrs(struct perf_evlist *evlist,
 #define perf_evlist__add_default_attrs(evlist, array) \
 	__perf_evlist__add_default_attrs(evlist, array, ARRAY_SIZE(array))
 
+int perf_evlist__add_dummy(struct perf_evlist *evlist);
+
 int perf_evlist__add_newtp(struct perf_evlist *evlist,
 			   const char *sys, const char *name, void *handler);