package/cgroupfs-v2-mount: new package

Currently, the cgroupfs-mount package only mounts a cgroup v1 hierarchy,
but v1 is considered legacy and obsolete, while v2 has been around for a
while now, and is required by some packages (e.g. podman whines about
v1).

cgroupfs-mount has not had a release in almost 8 years now, and only the
occasional commit since then and until more than 3 years ago. It's not
going to evolve...

Add a new package with a simple-enough sysv startup script, that mounts
the cgroup v2 hierarchy filesystem. For systemd, there's nothing to do,
as systemd handles the mount by itself.

Since both cgroup v1 and v2 use the same mountpoint, we can't have both
enabled at the same time, and thus we restrict the v2 to be hidden when
v1 is enabled (quite a few packages select the v1; changing those would
require that they be validated against v2 first...)

Note that, due to limitations in Kconfig, cgroupfs-v2-mount will appear
indented below cgroupfs-mount, because it has a (negative) dependency on
it. This spurious indentation is unfortunate and annoying, but benign;
fixing that would require breaking the dependency with a random Kconfig
symbol, which we don't have, and which we decided not to introduce just
for this one use-case (well, there's host-gnupg and host-gnupg2 that
have the exact same issue, but meh...)

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Fiona Klute <fiona.klute@gmx.de>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/Config.in

@@ -2809,6 +2809,7 @@ menu "System tools"
 	source "package/balena-engine/Config.in"
 	source "package/bubblewrap/Config.in"
 	source "package/cgroupfs-mount/Config.in"
+	source "package/cgroupfs-v2-mount/Config.in"
 	source "package/circus/Config.in"
 	source "package/conmon/Config.in"
 	source "package/containerd/Config.in"

package/cgroupfs-v2-mount/Config.in

@@ -0,0 +1,10 @@
+config BR2_PACKAGE_CGROUPFS_V2_MOUNT
+	bool "cgroupfs-v2-mount"
+	depends on !BR2_INIT_SYSTEMD
+	depends on !BR2_PACKAGE_CGROUPFS_MOUNT
+	help
+	  Mount the cgroup v2 hierarchy filesystem.
+
+comment "cgroupfs-v2-mount is incompatible with cgroupfs-mount"
+	depends on !BR2_INIT_SYSTEMD
+	depends on BR2_PACKAGE_CGROUPFS_MOUNT

package/cgroupfs-v2-mount/S30cgroupfs2

@@ -0,0 +1,44 @@
+#!/bin/sh
+
+DAEMON=cgroupfs2
+
+start() {
+	printf 'Mounting %s: ' "${DAEMON}"
+	mkdir -p /sys/fs/cgroup
+	mount -t cgroup2 none /sys/fs/cgroup
+	status=$?
+	if [ "$status" -eq 0 ]; then
+		echo "OK"
+	else
+		echo "FAIL"
+	fi
+	return "$status"
+}
+
+stop() {
+	printf 'Unmounting %s: ' "${DAEMON}"
+	umount /sys/fs/cgroup
+	status=$?
+	if [ "$status" -eq 0 ]; then
+		echo "OK"
+	else
+		echo "FAIL"
+	fi
+	return "$status"
+}
+
+restart() {
+	stop
+	start
+}
+
+case "$1" in
+	start|stop|restart)
+		"$1";;
+	reload)
+		# Restart, since there is no true "reload" feature.
+		restart;;
+	*)
+		echo "Usage: $0 {start|stop|restart|reload}"
+		exit 1
+esac

package/cgroupfs-v2-mount/cgroupfs-v2-mount.mk

@@ -0,0 +1,20 @@
+################################################################################
+#
+# cgroupfs-v2-mount
+#
+################################################################################
+
+CGROUPFS_V2_MOUNT_VERSION =
+CGROUPFS_V2_MOUNT_SITE =
+
+define CGROUPFS_V2_MOUNT_LINUX_CONFIG_FIXUPS
+	$(call KCONFIG_ENABLE_OPT,CONFIG_CGROUPS)
+endef
+
+define CGROUPFS_V2_MOUNT_INSTALL_INIT_SYSV
+	$(INSTALL) -m 0755 -D \
+		$(CGROUPFS_V2_MOUNT_PKGDIR)/S30cgroupfs2 \
+		$(TARGET_DIR)/etc/init.d/S30cgroupfs2
+endef
+
+$(eval $(generic-package))