From b1ce4fa3b6b8c423716b4ee6cbb56d12a438d737 Mon Sep 17 00:00:00 2001
From: Vladimir Kobal <vlad@prokk.net>
Date: Thu, 6 May 2021 17:02:02 +0300
Subject: [PATCH] Check the version of the default cgroup mountpoint (#11102)

---
 collectors/cgroups.plugin/sys_fs_cgroup.c | 17 +++++++++++++++--
 configure.ac                              |  1 +
 libnetdata/libnetdata.h                   |  4 ++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/collectors/cgroups.plugin/sys_fs_cgroup.c b/collectors/cgroups.plugin/sys_fs_cgroup.c
index 332404a1b..eea4d9ae7 100644
--- a/collectors/cgroups.plugin/sys_fs_cgroup.c
+++ b/collectors/cgroups.plugin/sys_fs_cgroup.c
@@ -160,7 +160,20 @@ static enum cgroups_type cgroups_try_detect_version()
     if(!cgroups2_available)
         return CGROUPS_V1;
 
-    // 2. check systemd compiletime setting
+#if defined CGROUP2_SUPER_MAGIC
+    // 2. check filesystem type for the default mountpoint
+    char filename[FILENAME_MAX + 1];
+    snprintfz(filename, FILENAME_MAX, "%s%s", netdata_configured_host_prefix, "/sys/fs/cgroup");
+    struct statfs fsinfo;
+    if (!statfs(filename, &fsinfo)) {
+        if (fsinfo.f_type == CGROUP2_SUPER_MAGIC)
+            return CGROUPS_V2;
+        if (fsinfo.f_type == CGROUP_SUPER_MAGIC)
+            return CGROUPS_V1;
+    }
+#endif
+
+    // 3. check systemd compiletime setting
     if ((systemd_setting = cgroups_detect_systemd("systemd --version")) == SYSTEMD_CGROUP_ERR)
         systemd_setting = cgroups_detect_systemd(SYSTEMD_CMD_RHEL);
 
@@ -174,7 +187,7 @@ static enum cgroups_type cgroups_try_detect_version()
         return CGROUPS_V1;
     }
 
-    // 3. if we are unified as on Fedora (default cgroups2 only mode)
+    // 4. if we are unified as on Fedora (default cgroups2 only mode)
     //    check kernel command line flag that can override that setting
     f = fopen("/proc/cmdline", "r");
     if (!f) {
diff --git a/configure.ac b/configure.ac
index 03672c551..031351ab7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -249,6 +249,7 @@ AC_HEADER_RESOLV
 AC_CHECK_HEADERS_ONCE([sys/prctl.h])
 AC_CHECK_HEADERS_ONCE([sys/vfs.h])
 AC_CHECK_HEADERS_ONCE([sys/statfs.h])
+AC_CHECK_HEADERS_ONCE([linux/magic.h])
 AC_CHECK_HEADERS_ONCE([sys/statvfs.h])
 AC_CHECK_HEADERS_ONCE([sys/mount.h])
 
diff --git a/libnetdata/libnetdata.h b/libnetdata/libnetdata.h
index 5481d003b..77a1bbe7f 100644
--- a/libnetdata/libnetdata.h
+++ b/libnetdata/libnetdata.h
@@ -118,6 +118,10 @@ extern "C" {
 #include <sys/statfs.h>
 #endif
 
+#ifdef HAVE_LINUX_MAGIC_H
+#include <linux/magic.h>
+#endif
+
 #ifdef HAVE_SYS_MOUNT_H
 #include <sys/mount.h>
 #endif