pinetainer: add cgroups init script

This script sets up the cgroup v2 hierarchy that will be used
for resource control between the system software and the virtual
machines.

board/pinetainer/rootfs-overlay/etc/init.d/S00cgroups.sh

@@ -0,0 +1,109 @@
+#!/bin/sh
+
+# The directory where the cgroup2 hierarchy will be mounted
+readonly CGROUP_HIERARCHY_MOUNTPOINT=/sys/fs/cgroup
+
+# The cgroup por system (i.e. non VM) processes
+readonly SYSTEM_CGROUP=system
+
+# The total number of CPU shares that will be distributed between the system and Pinetainers,
+# via the cpu controller of cgroupsv2
+readonly TOTAL_CPU_SHARES=1000
+
+# The total number of IOPS shares that will be distributed between the system and Pinetainers,
+# via the io controller of cgroupsv2
+readonly TOTAL_IOPS_SHARES=1000
+
+# System processes can use at least this percentage of the CPU time.
+# 8% is equivalent to ~33% of a CPU core
+readonly MINIMUM_SYSTEM_CPU_ALLOCATION=8
+
+# System processes can use at least this percentage of the IO throughput
+readonly MINIMUM_SYSTEM_IOPS_ALLOCATION=10
+
+# The maximum amount of memory that processes in the system cgroup are allowed to use,
+# in MiB, with a M suffix. If this threshold is exceeded, the OOM killer will kill processes
+# cin the group to restore available memory. The processes in the cgroup will be put under
+# high memory pressure when only less than the 25% of this memory is available
+readonly MAXIMUM_SYSTEM_MEMORY=192M
+
+# Limit the maximum number of processes that processes in the system cgroup can spawn.
+readonly MAXIMUM_SYSTEM_PIDS=512
+
+# The file that represents high-level status information about the cgroups configuration
+# in the system
+readonly CGROUPS_INITIALIZED_STATUS_FILE=/run/cgroups_status
+
+start() {
+	printf 'Setting up cgroups: '
+
+	if
+	# Mount hierarchy and controllers
+	mount -t cgroup2 cgroup2 "$CGROUP_HIERARCHY_MOUNTPOINT" && \
+	echo '+cpu +io +memory +pids' > "$CGROUP_HIERARCHY_MOUNTPOINT/cgroup.subtree_control" && \
+	mkdir "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP" && \
+	# Move all proccesses to the system cgroup. This includes some kernel threads
+	for pid in $(ps -A -o pid=); do
+		echo "$pid" > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/cgroup.procs" || true
+	done && \
+	# Now setup the system cgroup controllers
+	echo $(((TOTAL_CPU_SHARES * MINIMUM_SYSTEM_CPU_ALLOCATION) / 100)) > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/cpu.weight" && \
+	echo $(((TOTAL_IOPS_SHARES * MINIMUM_SYSTEM_IOPS_ALLOCATION) / 100)) > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/io.bfq.weight" && \
+	maximum_system_memory_megs="${MAXIMUM_SYSTEM_MEMORY%M}" && \
+	high_system_memory_megs=$(((maximum_system_memory_megs * 3) / 4)) && \
+	low_system_memory_megs=$((maximum_system_memory_megs / 2)) && \
+	echo "${maximum_system_memory_megs}M" > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/memory.max" && \
+	echo "${high_system_memory_megs}M" > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/memory.high" && \
+	echo "${low_system_memory_megs}M" > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/memory.low" && \
+	echo $MAXIMUM_SYSTEM_PIDS > "$CGROUP_HIERARCHY_MOUNTPOINT/$SYSTEM_CGROUP/pids.max" && \
+	# Create cgroup status file
+	touch "$CGROUPS_INITIALIZED_STATUS_FILE"
+	then
+		echo 'OK'
+	else
+		echo 'FAIL'
+	fi
+}
+
+# We read words from input files on purpose
+# shellcheck disable=SC2013
+stop() {
+	printf 'Tearing down cgroups: '
+
+	if if [ -f "$CGROUPS_INITIALIZED_STATUS_FILE" ]; then
+		# Remove cgroup status file
+		rm -f "$CGROUPS_INITIALIZED_STATUS_FILE" && \
+		# Move all processes to the root cgroup
+		for pid in $(ps -A -o pid=); do
+			echo "$pid" > "$CGROUP_HIERARCHY_MOUNTPOINT/cgroup.procs" || true
+		done && \
+		# Remove all children cgroups
+		find "$CGROUP_HIERARCHY_MOUNTPOINT"/* -type d -exec rm {} \; && \
+		# Remove all the controllers. This also resets their configuration
+		shell_options_restore_cmds="$(set +o)" && \
+		set -f && \
+		for controller in $(cat "$CGROUP_HIERARCHY_MOUNTPOINT/cgroup.controllers"); do
+			echo "-$controller" > "$CGROUP_HIERARCHY_MOUNTPOINT/cgroup.subtree_control"
+		done && \
+		eval "$shell_options_restore_cmds" && \
+		# Umount the cgroup hierarchy
+		umount "$CGROUP_HIERARCHY_MOUNTPOINT"
+	fi; then
+		echo 'OK'
+	else
+		echo 'FAIL'
+	fi
+}
+
+restart() {
+	stop && start
+}
+
+case "$1" in
+	start)			start;;
+	stop)			stop;;
+	restart|reload)	restart;;
+	status)			[ -f "$CGROUPS_INITIALIZED_STATUS_FILE" ];;
+	*)				echo "Usage: $0 {start|stop|restart|reload|status}"
+					exit 1
+esac