perf cgroup: Add evlist__findnew_cgroup()

Similar to machine__findnew_thread(), etc, i.e. try to find, get a
refcount if found and return it, otherwise return a new cgroup object.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-im1omevlihhyneiic4nl3g24@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cgroup.c

@@ -128,18 +128,21 @@ static struct cgroup *cgroup__new(char *name)
 	return NULL;
 }
 
+struct cgroup *evlist__findnew_cgroup(struct perf_evlist *evlist, char *name)
+{
+	struct cgroup *cgroup = evlist__find_cgroup(evlist, name);
+
+	return cgroup ?: cgroup__new(name);
+}
+
 static int add_cgroup(struct perf_evlist *evlist, char *str)
 {
 	struct perf_evsel *counter;
-	struct cgroup *cgrp = evlist__find_cgroup(evlist, str);
+	struct cgroup *cgrp = evlist__findnew_cgroup(evlist, str);
 	int n;
 
-	if (!cgrp) {
-		cgrp = cgroup__new(str);
-		if (!cgrp)
-			return -1;
-	}
-
+	if (!cgrp)
+		return -1;
 	/*
 	 * find corresponding event
 	 * if add cgroup N, then need to find event N

tools/perf/util/cgroup.h

@@ -18,6 +18,10 @@ extern int nr_cgroups; /* number of explicit cgroups defined */
 struct cgroup *cgroup__get(struct cgroup *cgroup);
 void cgroup__put(struct cgroup *cgroup);
 
+struct perf_evlist;
+
+struct cgroup *evlist__findnew_cgroup(struct perf_evlist *evlist, char *name);
+
 int parse_cgroups(const struct option *opt, const char *str, int unset);
 
 #endif /* __CGROUP_H__ */