cgroups: enhance support

Add a possibility to:
* Set a cgroup name for a service,

* Set a cgroup name prefix for services that don't have an explicit cgroup
name set by the previous feature.
This allows defining, for example, a root "services" cgroup, under which
children cgroups for particular services are kept,

* Add a service to a controller without needing to set any of its settings,

* Keep a service cgroup when it becomes empty (for example to keep between
service restarts some cgroup settings that were set outside OpenRC).

These functionalities allow configuration of a service cgroup name for v1
controllers and v2 (unified) hierarchy; the service name in the "openrc"
hierarchy is not affected by these settings.

The default values are set in a way so not to result in any change of
services cgroup behavior unless specifically configured in a different way
by an user.

Author: maciejsszmigiero

etc/rc.conf

@@ -232,6 +232,19 @@ rc_tty_number=12
 # It must be set to yes in this file if you want this functionality.
 #rc_cgroup_memory_use_hierarchy="NO"
 
+# Sets cgroup name for a service (for cgroups v1 controllers and cgroups v2).
+# If empty, the service name will be used with a "openrc_" prefix (the whole
+# name then optionally prefixed by rc_cgroup_name_prefix).
+# You'll most certainly want a different name for each service, so set this
+# setting in /etc/conf.d/foo (for a service named foo) instead of doing it here.
+# Could contain intermediate cgroups in the path, like "services/foo".
+#rc_cgroup_name=""
+
+# Sets cgroup name prefix for services that have rc_cgroup_name unset.
+# For example, with rc_cgroup_name_prefix="services" some service named "foo"
+# would get a cgroup name of "services/openrc_foo".
+#rc_cgroup_name_prefix=""
+
 # The following settings allow you to set up values for the cgroups version 1
 # controllers for your services.
 # They can be set in this file;, however, if you do this, the settings
@@ -246,6 +259,11 @@ rc_tty_number=12
 # cpu.shares 512
 # "
 #
+# You can also set a variable to a special "add" value, which will add
+# the service to the relevant controller without changing any of its settings.
+# For example, to just add your service to the cpu controller use:
+# rc_cgroup_cpu="add"
+#
 # For more information about the adjustments that can be made with
 # cgroups version 1, see Documentation/cgroups-v1/* in the linux kernel
 # source tree.
@@ -280,6 +298,13 @@ rc_tty_number=12
 # Set the pids controller settings for this service.
 #rc_cgroup_pids=""
 
+# Set this to YES if you do not want a service cgroup removed when it
+# becomes empty (for example if you want to keep between service restarts
+# some settings that were set outside OpenRC).
+# If you want a different setting for each service, place the setting in
+# /etc/conf.d/foo for service foo.
+# rc_cgroup_keep="NO"
+
 # Set this to YES if you want all of the processes in a service's cgroup
 # killed when the service is stopped or restarted.
 # Be aware that setting this to yes means all of a service's

sh/rc-cgroup.sh

@@ -11,6 +11,17 @@
 extra_stopped_commands="${extra_stopped_commands} cgroup_cleanup"
 description_cgroup_cleanup="Kill all processes in the cgroup"
 
+cgroup_name()
+{
+	if [ -z "${rc_cgroup_name}" ]; then
+		rc_cgroup_name="openrc_${RC_SVCNAME}"
+		[ -n "${rc_cgroup_name_prefix}" ] &&
+			rc_cgroup_name="${rc_cgroup_name_prefix}/${rc_cgroup_name}"
+	fi
+
+	printf "%s" "${rc_cgroup_name}"
+}
+
 cgroup_find_path()
 {
 	local OIFS name dir result
@@ -53,9 +64,16 @@ cgroup_set_values()
 	local controller h
 	controller="$1"
 	h=$(cgroup_find_path "$1")
-	cgroup="/sys/fs/cgroup/${1}${h}openrc_${RC_SVCNAME}"
+	cgroup="/sys/fs/cgroup/${1}${h}$(cgroup_name)"
 	[ -d "$cgroup" ] || mkdir -p "$cgroup"
 
+	if [ -w "$cgroup/tasks" ]; then
+		veinfo "$RC_SVCNAME: adding to $cgroup/tasks"
+		printf "%d" 0 > "$cgroup/tasks"
+	fi
+
+	[ "$2" = "add" ] && return 0
+
 	set -- $2
 	local name val
 	while [ -n "$1" ] && [ "$controller" != "cpuacct" ]; do
@@ -82,11 +100,6 @@ cgroup_set_values()
 		printf "%s" "$val" > "$cgroup/$name"
 	fi
 
-	if [ -w "$cgroup/tasks" ]; then
-		veinfo "$RC_SVCNAME: adding to $cgroup/tasks"
-		printf "%d" 0 > "$cgroup/tasks"
-	fi
-
 	return 0
 }
 
@@ -156,10 +169,12 @@ cgroup2_find_path()
 
 cgroup2_remove()
 {
+	yesno "${rc_cgroup_keep:-no}" && return 0
+
 	local cgroup_path rc_cgroup_path
 	cgroup_path="$(cgroup2_find_path)"
 	[ -z "${cgroup_path}" ] && return 0
-	rc_cgroup_path="${cgroup_path}/${RC_SVCNAME}"
+	rc_cgroup_path="${cgroup_path}/$(cgroup_name)"
 	[ ! -d "${rc_cgroup_path}" ] ||
 		[ ! -e "${rc_cgroup_path}"/cgroup.events ] &&
 		return 0
@@ -182,8 +197,8 @@ cgroup2_set_limits()
 	local cgroup_path
 	cgroup_path="$(cgroup2_find_path)"
 	[ -d "${cgroup_path}" ] || return 0
-	rc_cgroup_path="${cgroup_path}/${RC_SVCNAME}"
-	[ ! -d "${rc_cgroup_path}" ] && mkdir "${rc_cgroup_path}"
+	rc_cgroup_path="${cgroup_path}/$(cgroup_name)"
+	[ ! -d "${rc_cgroup_path}" ] && mkdir -p "${rc_cgroup_path}"
 	[ -f "${rc_cgroup_path}"/cgroup.procs ] &&
 		printf 0 > "${rc_cgroup_path}"/cgroup.procs
 	[ -z "${rc_cgroup_settings}" ] && return 0