Add boot.Loader state

This is to prevent an started container from restoring. It can
also be extended to other checks in the future.

Updates #1956

PiperOrigin-RevId: 627762283

runsc/boot/controller.go

@@ -222,6 +222,11 @@ type containerManager struct {
 func (cm *containerManager) StartRoot(cid *string, _ *struct{}) error {
 	log.Debugf("containerManager.StartRoot, cid: %s", *cid)
 	// Tell the root container to start and wait for the result.
+	return cm.onStart()
+}
+
+// onStart notifies that sandbox is ready to start and wait for the result.
+func (cm *containerManager) onStart() error {
 	cm.startChan <- struct{}{}
 	if err := <-cm.startResultChan; err != nil {
 		return fmt.Errorf("starting sandbox: %v", err)
@@ -461,6 +466,12 @@ type RestoreOpts struct {
 func (cm *containerManager) Restore(o *RestoreOpts, _ *struct{}) error {
 	log.Debugf("containerManager.Restore")
 
+	if cm.l.state == restoring {
+		return fmt.Errorf("restore is already in progress")
+	}
+	if cm.l.state == started {
+		return fmt.Errorf("cannot restore a started container")
+	}
 	if len(o.Files) == 0 {
 		return fmt.Errorf("at least one file must be passed to Restore")
 	}
@@ -480,6 +491,7 @@ func (cm *containerManager) Restore(o *RestoreOpts, _ *struct{}) error {
 	}
 
 	r := restorer{container: &cm.l.root, stateFile: stateFile}
+	cm.l.state = restoring
 
 	fileIdx := 1
 	if o.HavePagesFile {
@@ -510,14 +522,7 @@ func (cm *containerManager) Restore(o *RestoreOpts, _ *struct{}) error {
 	if err := r.restore(cm.l); err != nil {
 		return err
 	}
-
-	// Tell the root container to start and wait for the result.
-	cm.startChan <- struct{}{}
-	if err := <-cm.startResultChan; err != nil {
-		return fmt.Errorf("starting sandbox: %v", err)
-	}
-
-	return nil
+	return cm.onStart()
 }
 
 // Wait waits for the init process in the given container.

runsc/boot/loader.go

@@ -151,6 +151,18 @@ type containerInfo struct {
 	nvidiaDriverVersion string
 }
 
+type loaderState int
+
+const (
+	// created indicates that the Loader has been created, but not started yet.
+	created loaderState = iota
+	// started indicates that the Loader has been started.
+	started
+	// restoring indicates that the Loader has been created and is restoring
+	// containers. It will change to started after restore is completed.
+	restoring
+)
+
 // Loader keeps state needed to start the kernel and run the container.
 type Loader struct {
 	// k is the kernel.
@@ -192,6 +204,9 @@ type Loader struct {
 	// mu guards the fields below.
 	mu sync.Mutex
 
+	// state is guarded by mu.
+	state loaderState
+
 	// sharedMounts holds VFS mounts that may be shared between containers within
 	// the same pod. It is mapped by mount source.
 	sharedMounts map[string]*vfs.Mount
@@ -847,7 +862,11 @@ func (l *Loader) run() error {
 
 	log.Infof("Process should have started...")
 	l.watchdog.Start()
-	return l.k.Start()
+	if err := l.k.Start(); err != nil {
+		return err
+	}
+	l.state = started
+	return nil
 }
 
 // createSubcontainer creates a new container inside the sandbox.