add pre checkpoint

Signed-off-by: Zhuohan Chen <chen_zhuohan@163.com>

libpod/container_api.go

@@ -706,6 +706,13 @@ type ContainerCheckpointOptions struct {
 	// IgnoreVolumes tells the API to not export or not to import
 	// the content of volumes associated with the container
 	IgnoreVolumes bool
+	// Pre Checkpoint container and leave container running
+	PreCheckPoint bool
+	// Dump container with Pre Checkpoint images
+	WithPrevious bool
+	// ImportPrevious tells the API to restore container with two
+	// images. One is TargetFile, the other is ImportPrevious.
+	ImportPrevious string
 }
 
 // Checkpoint checkpoints a container
@@ -718,6 +725,12 @@ func (c *Container) Checkpoint(ctx context.Context, options ContainerCheckpointO
 		}
 	}
 
+	if options.WithPrevious {
+		if err := c.canWithPrevious(); err != nil {
+			return err
+		}
+	}
+
 	if !c.batched {
 		c.lock.Lock()
 		defer c.lock.Unlock()