perf cgroup: Maintain cgroup hierarchy

Each cgroup is kept in the perf_env's cgroup_tree sorted by the cgroup
id.  Hist entries have cgroup id can compare it directly and later it
can be used to find a group name using this tree.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200325124536.2800725-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/cgroup.h b/tools/perf/util/cgroup.h
index 2ec11f0..e98d597 100644
--- a/tools/perf/util/cgroup.h
+++ b/tools/perf/util/cgroup.h
@@ -3,16 +3,19 @@
 #define __CGROUP_H__
 
 #include <linux/refcount.h>
+#include <linux/rbtree.h>
+#include "util/env.h"
 
 struct option;
 
 struct cgroup {
-	char *name;
-	int fd;
-	refcount_t refcnt;
+	struct rb_node		node;
+	u64			id;
+	char			*name;
+	int			fd;
+	refcount_t		refcnt;
 };
 
-
 extern int nr_cgroups; /* number of explicit cgroups defined */
 
 struct cgroup *cgroup__get(struct cgroup *cgroup);
@@ -26,4 +29,10 @@ void evlist__set_default_cgroup(struct evlist *evlist, struct cgroup *cgroup);
 
 int parse_cgroups(const struct option *opt, const char *str, int unset);
 
+struct cgroup *cgroup__findnew(struct perf_env *env, uint64_t id,
+			       const char *path);
+struct cgroup *cgroup__find(struct perf_env *env, uint64_t id);
+
+void perf_env__purge_cgroups(struct perf_env *env);
+
 #endif /* __CGROUP_H__ */