libct/cg: allow Set(nil)

As the cgroup config is already supplied during Apply(), allow Set()
to accept nil -- in which case it uses the resources from the config.

While at it, don't forget to save the new resources into the manager's
internal state (previously only fs driver did that).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs/fs.go

@@ -276,7 +276,7 @@ func (m *manager) GetStats() (*cgroups.Stats, error) {
 
 func (m *manager) Set(r *configs.Resources) error {
 	if r == nil {
-		return nil
+		r = m.cgroups.Resources
 	}
 
 	// If Paths are set, then we are just joining cgroups paths
@@ -308,6 +308,7 @@ func (m *manager) Set(r *configs.Resources) error {
 		}
 	}
 
+	m.cgroups.Resources = r
 	return nil
 }
 

libcontainer/cgroups/fs2/fs2.go

@@ -164,6 +164,9 @@ func (m *manager) Path(_ string) string {
 }
 
 func (m *manager) Set(r *configs.Resources) error {
+	if r == nil {
+		r = m.config.Resources
+	}
 	if err := m.getControllers(); err != nil {
 		return err
 	}

libcontainer/cgroups/systemd/v1.go

@@ -337,6 +337,9 @@ func (m *legacyManager) Set(r *configs.Resources) error {
 	if m.cgroups.Paths != nil {
 		return nil
 	}
+	if r == nil {
+		r = m.cgroups.Resources
+	}
 	if r.Unified != nil {
 		return cgroups.ErrV1NoUnified
 	}
@@ -392,6 +395,7 @@ func (m *legacyManager) Set(r *configs.Resources) error {
 		}
 	}
 
+	m.cgroups.Resources = r
 	return nil
 }
 

libcontainer/cgroups/systemd/v2.go

@@ -426,6 +426,9 @@ func (m *unifiedManager) GetStats() (*cgroups.Stats, error) {
 }
 
 func (m *unifiedManager) Set(r *configs.Resources) error {
+	if r == nil {
+		r = m.cgroups.Resources
+	}
 	dbusConnection, err := getDbusConnection(m.rootless)
 	if err != nil {
 		return err
@@ -471,7 +474,12 @@ func (m *unifiedManager) Set(r *configs.Resources) error {
 	if err != nil {
 		return err
 	}
-	return fsMgr.Set(r)
+	if err := fsMgr.Set(r); err != nil {
+		return err
+	}
+
+	m.cgroups.Resources = r
+	return nil
 }
 
 func (m *unifiedManager) GetPaths() map[string]string {