[PATCH 2/3] perf tools: Add cgroup_is_v2() helper

[Namhyung Kim <namhyung@kernel.org>]

The cgroup_is_v2() is to check if the given subsystem is mounted on
cgroup v2 or not.  It'll be used by BPF cgroup code later.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/cgroup.c | 19 +++++++++++++++++++
 tools/perf/util/cgroup.h |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/tools/perf/util/cgroup.c b/tools/perf/util/cgroup.c
index ef18c988c681..48ec79211270 100644
--- a/tools/perf/util/cgroup.c
+++ b/tools/perf/util/cgroup.c
@@ -9,6 +9,7 @@
 #include <linux/zalloc.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/statfs.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <string.h>
@@ -70,6 +71,24 @@ int read_cgroup_id(struct cgroup *cgrp)
 }
 #endif  /* HAVE_FILE_HANDLE */
 
+#ifndef CGROUP2_SUPER_MAGIC
+#define CGROUP2_SUPER_MAGIC  0x63677270
+#endif
+
+int cgroup_is_v2(const char *subsys)
+{
+	char mnt[PATH_MAX + 1];
+	struct statfs stbuf;
+
+	if (cgroupfs_find_mountpoint(mnt, PATH_MAX + 1, subsys))
+		return -1;
+
+	if (statfs(mnt, stbuf) < 0)
+		return -1;
+
+	return (stbuf.f_type == CGROUP2_SUPER_MAGIC);
+}
+
 static struct cgroup *evlist__find_cgroup(struct evlist *evlist, const char *str)
 {
 	struct evsel *counter;
diff --git a/tools/perf/util/cgroup.h b/tools/perf/util/cgroup.h
index 707adbe25123..1549ec2fd348 100644
--- a/tools/perf/util/cgroup.h
+++ b/tools/perf/util/cgroup.h
@@ -47,4 +47,6 @@ int read_cgroup_id(struct cgroup *cgrp)
 }
 #endif  /* HAVE_FILE_HANDLE */
 
+int cgroup_is_v2(const char *subsys);
+
 #endif /* __CGROUP_H__ */
-- 
2.32.0.272.g935e593368-goog