perf tools: Allow creation of cgroup without open

This is a preparation for a test case of expanding events for multiple
cgroups.  Instead of using real system cgroup, the test will use fake
cgroups so it needs a way to have them without a open file descriptor.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200924124455.336326-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-stat.c

@@ -2235,7 +2235,7 @@ int cmd_stat(int argc, const char **argv)
 		}
 
 		if (evlist__expand_cgroup(evsel_list, stat_config.cgroup_list,
-					  &stat_config.metric_events) < 0)
+					  &stat_config.metric_events, true) < 0)
 			goto out;
 	}
 

tools/perf/util/cgroup.c

@@ -51,7 +51,7 @@ static struct cgroup *evlist__find_cgroup(struct evlist *evlist, const char *str
 	return NULL;
 }
 
-static struct cgroup *cgroup__new(const char *name)
+static struct cgroup *cgroup__new(const char *name, bool do_open)
 {
 	struct cgroup *cgroup = zalloc(sizeof(*cgroup));
 
@@ -61,9 +61,14 @@ static struct cgroup *cgroup__new(const char *name)
 		cgroup->name = strdup(name);
 		if (!cgroup->name)
 			goto out_err;
-		cgroup->fd = open_cgroup(name);
-		if (cgroup->fd == -1)
-			goto out_free_name;
+
+		if (do_open) {
+			cgroup->fd = open_cgroup(name);
+			if (cgroup->fd == -1)
+				goto out_free_name;
+		} else {
+			cgroup->fd = -1;
+		}
 	}
 
 	return cgroup;
@@ -79,7 +84,7 @@ struct cgroup *evlist__findnew_cgroup(struct evlist *evlist, const char *name)
 {
 	struct cgroup *cgroup = evlist__find_cgroup(evlist, name);
 
-	return cgroup ?: cgroup__new(name);
+	return cgroup ?: cgroup__new(name, true);
 }
 
 static int add_cgroup(struct evlist *evlist, const char *str)
@@ -197,7 +202,7 @@ int parse_cgroups(const struct option *opt, const char *str,
 }
 
 int evlist__expand_cgroup(struct evlist *evlist, const char *str,
-			  struct rblist *metric_events)
+			  struct rblist *metric_events, bool open_cgroup)
 {
 	struct evlist *orig_list, *tmp_list;
 	struct evsel *pos, *evsel, *leader;
@@ -240,7 +245,7 @@ int evlist__expand_cgroup(struct evlist *evlist, const char *str,
 			if (!name)
 				goto out_err;
 
-			cgrp = cgroup__new(name);
+			cgrp = cgroup__new(name, open_cgroup);
 			free(name);
 			if (cgrp == NULL)
 				goto out_err;

tools/perf/util/cgroup.h

@@ -26,7 +26,7 @@ struct rblist;
 
 struct cgroup *evlist__findnew_cgroup(struct evlist *evlist, const char *name);
 int evlist__expand_cgroup(struct evlist *evlist, const char *cgroups,
-			  struct rblist *metric_events);
+			  struct rblist *metric_events, bool open_cgroup);
 
 void evlist__set_default_cgroup(struct evlist *evlist, struct cgroup *cgroup);