Add systemd resource budgets with TOML profiles

internal/budget/bus.go

@@ -0,0 +1,113 @@
+package budget
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/godbus/dbus/v5"
+)
+
+const api = "org.freedesktop.systemd1"
+const noUnit = api + ".NoSuchUnit"
+const noPID = "org.freedesktop.DBus.Error.UnixProcessIdUnknown"
+
+type unit struct {
+	Name        string
+	Description string
+	Load        string
+	Active      string
+	Sub         string
+	Following   string
+	Path        dbus.ObjectPath
+	Job         uint32
+	JobType     string
+	JobPath     dbus.ObjectPath
+}
+
+type unitState struct {
+	Active string
+	Group  string
+}
+
+type unitCtl interface {
+	Units() ([]unit, error)
+	Group(string) (string, error)
+	Set(string, []property) error
+	Start(string, []property) error
+	State(string) (unitState, error)
+	Stop(string) error
+}
+
+type manager struct {
+	conn *dbus.Conn
+	obj  dbus.BusObject
+}
+
+type auxiliary struct {
+	Name       string
+	Properties []property
+}
+
+func connect() (*manager, error) {
+	conn, err := dbus.ConnectSessionBus()
+	if err != nil {
+		return nil, err
+	}
+	return &manager{conn: conn, obj: conn.Object(api, "/org/freedesktop/systemd1")}, nil
+}
+
+func busError(err error, name string) bool {
+	var e dbus.Error
+	return errors.As(err, &e) && e.Name == name
+}
+
+func (m *manager) Units() ([]unit, error) {
+	var units []unit
+	err := m.obj.Call(api+".Manager.ListUnits", 0).Store(&units)
+	return units, err
+}
+
+func (m *manager) object(name string) (dbus.BusObject, error) {
+	var path dbus.ObjectPath
+	if err := m.obj.Call(api+".Manager.GetUnit", 0, name).Store(&path); err != nil {
+		return nil, err
+	}
+	return m.conn.Object(api, path), nil
+}
+
+func (m *manager) Group(name string) (string, error) {
+	obj, err := m.object(name)
+	if err != nil {
+		return "", err
+	}
+	kind := name[strings.LastIndex(name, ".")+1:]
+	kind = strings.ToUpper(kind[:1]) + kind[1:]
+	var group string
+	err = obj.StoreProperty(api+"."+kind+".ControlGroup", &group)
+	return group, err
+}
+
+func (m *manager) Set(name string, values []property) error {
+	return m.obj.Call(api+".Manager.SetUnitProperties", 0, name, true, values).Err
+}
+
+func (m *manager) Start(name string, values []property) error {
+	return m.obj.Call(api+".Manager.StartTransientUnit", 0, name, "fail", values, []auxiliary{}).Err
+}
+
+func (m *manager) State(name string) (unitState, error) {
+	obj, err := m.object(name)
+	if err != nil {
+		return unitState{}, err
+	}
+	var state unitState
+	if err = obj.StoreProperty(api+".Unit.ActiveState", &state.Active); err != nil {
+		return unitState{}, err
+	}
+	err = obj.StoreProperty(api+".Scope.ControlGroup", &state.Group)
+	return state, err
+}
+
+func (m *manager) Stop(name string) error {
+	return m.obj.Call(api+".Manager.StopUnit", 0, name, "replace").Err
+}