contrib/check-config.sh: support for cgroupv2

Before:

> Generally Necessary:
> - cgroup hierarchy: nonexistent??
>     (see https://github.com/tianon/cgroupfs-mount)

After:

> Generally Necessary:
> - cgroup hierarchy: cgroupv2

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

contrib/check-config.sh

@@ -155,18 +155,22 @@ echo
 echo 'Generally Necessary:'
 
 echo -n '- '
-cgroupSubsystemDir="$(awk '/[, ](cpu|cpuacct|cpuset|devices|freezer|memory)[, ]/ && $3 == "cgroup" { print $2 }' /proc/mounts | head -n1)"
-cgroupDir="$(dirname "$cgroupSubsystemDir")"
-if [ -d "$cgroupDir/cpu" ] || [ -d "$cgroupDir/cpuacct" ] || [ -d "$cgroupDir/cpuset" ] || [ -d "$cgroupDir/devices" ] || [ -d "$cgroupDir/freezer" ] || [ -d "$cgroupDir/memory" ]; then
-	echo "$(wrap_good 'cgroup hierarchy' 'properly mounted') [$cgroupDir]"
+if [ "$(stat -f -c %t /sys/fs/cgroup 2> /dev/null)" = '63677270' ]; then
+	echo "$(wrap_good 'cgroup hierarchy' 'cgroupv2')"
 else
-	if [ "$cgroupSubsystemDir" ]; then
-		echo "$(wrap_bad 'cgroup hierarchy' 'single mountpoint!') [$cgroupSubsystemDir]"
+	cgroupSubsystemDir="$(awk '/[, ](cpu|cpuacct|cpuset|devices|freezer|memory)[, ]/ && $3 == "cgroup" { print $2 }' /proc/mounts | head -n1)"
+	cgroupDir="$(dirname "$cgroupSubsystemDir")"
+	if [ -d "$cgroupDir/cpu" ] || [ -d "$cgroupDir/cpuacct" ] || [ -d "$cgroupDir/cpuset" ] || [ -d "$cgroupDir/devices" ] || [ -d "$cgroupDir/freezer" ] || [ -d "$cgroupDir/memory" ]; then
+		echo "$(wrap_good 'cgroup hierarchy' 'properly mounted') [$cgroupDir]"
 	else
-		wrap_bad 'cgroup hierarchy' 'nonexistent??'
+		if [ "$cgroupSubsystemDir" ]; then
+			echo "$(wrap_bad 'cgroup hierarchy' 'single mountpoint!') [$cgroupSubsystemDir]"
+		else
+			wrap_bad 'cgroup hierarchy' 'nonexistent??'
+		fi
+		EXITCODE=1
+		echo "    $(wrap_color '(see https://github.com/tianon/cgroupfs-mount)' yellow)"
 	fi
-	EXITCODE=1
-	echo "    $(wrap_color '(see https://github.com/tianon/cgroupfs-mount)' yellow)"
 fi
 
 if [ "$(cat /sys/module/apparmor/parameters/enabled 2> /dev/null)" = 'Y' ]; then