libct/cg/sd: add renew dbus connection

[@kolyshkin: doc nits, use dbus.ErrClosed and isDbusError]

Signed-off-by: Shiming Zhang <wzshiming@foxmail.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/systemd/dbus.go

@@ -7,6 +7,8 @@ import (
 	"sync"
 
 	systemdDbus "github.com/coreos/go-systemd/v22/dbus"
+	dbus "github.com/godbus/dbus/v5"
+	"github.com/sirupsen/logrus"
 )
 
 type dbusConnManager struct {
@@ -57,3 +59,31 @@ func (d *dbusConnManager) newConnection() (*systemdDbus.Conn, error) {
 	}
 	return systemdDbus.NewWithContext(context.TODO())
 }
+
+// resetConnection resets the connection to its initial state
+// (so it can be reconnected if necessary).
+func (d *dbusConnManager) resetConnection(conn *systemdDbus.Conn) {
+	d.Lock()
+	defer d.Unlock()
+	if d.conn != nil && d.conn == conn {
+		d.conn.Close()
+		d.conn = nil
+	}
+}
+
+var errDbusConnClosed = dbus.ErrClosed.Error()
+
+// checkAndReconnect checks if the connection is disconnected,
+// and tries reconnect if it is.
+func (d *dbusConnManager) checkAndReconnect(conn *systemdDbus.Conn, err error) {
+	if !isDbusError(err, errDbusConnClosed) {
+		return
+	}
+	d.resetConnection(conn)
+
+	// Try to reconnect
+	_, err = d.getConnection()
+	if err != nil {
+		logrus.Warnf("Dbus disconnected and failed to reconnect: %s", err)
+	}
+}

libcontainer/cgroups/systemd/v1.go

@@ -173,6 +173,7 @@ func (m *legacyManager) Apply(pid int) error {
 	properties = append(properties, c.SystemdProps...)
 
 	if err := startUnit(dbusConnection, unitName, properties); err != nil {
+		m.dbus.checkAndReconnect(dbusConnection, err)
 		return err
 	}
 
@@ -376,6 +377,7 @@ func (m *legacyManager) Set(container *configs.Config) error {
 	}
 
 	if err := dbusConnection.SetUnitProperties(getUnitName(container.Cgroups), true, properties...); err != nil {
+		m.dbus.checkAndReconnect(dbusConnection, err)
 		_ = m.Freeze(targetFreezerState)
 		return err
 	}

libcontainer/cgroups/systemd/v2.go

@@ -288,6 +288,7 @@ func (m *unifiedManager) Apply(pid int) error {
 	properties = append(properties, c.SystemdProps...)
 
 	if err := startUnit(dbusConnection, unitName, properties); err != nil {
+		m.dbus.checkAndReconnect(dbusConnection, err)
 		return errors.Wrapf(err, "error while starting unit %q with properties %+v", unitName, properties)
 	}
 
@@ -462,6 +463,7 @@ func (m *unifiedManager) Set(container *configs.Config) error {
 	}
 
 	if err := dbusConnection.SetUnitProperties(getUnitName(m.cgroups), true, properties...); err != nil {
+		m.dbus.checkAndReconnect(dbusConnection, err)
 		_ = m.Freeze(targetFreezerState)
 		return errors.Wrap(err, "error while setting unit properties")
 	}