enhance preload timing issue

cmd/control/preload.go

@@ -14,6 +14,8 @@ import (
 	"github.com/codegangsta/cli"
 
 	dockerClient "github.com/docker/engine-api/client"
+	"github.com/docker/engine-api/types"
+	"github.com/rancher/os/config"
 	"github.com/rancher/os/docker"
 	"github.com/rancher/os/log"
 )
@@ -90,10 +92,17 @@ func PreloadImages(clientFactory func() (dockerClient.APIClient, error), imagesD
 			clientInitialized = true
 		}
 
-		log.Infof("Loading image %s", filename)
-		if _, err = client.ImageLoad(context.Background(), imageReader, false); err != nil {
+		var imageLoadResponse types.ImageLoadResponse
+		if imageLoadResponse, err = client.ImageLoad(context.Background(), imageReader, false); err != nil {
 			return err
 		}
+		cfg := config.LoadConfig()
+		if cfg.Rancher.PreloadWait {
+			if _, err := ioutil.ReadAll(imageLoadResponse.Body); err != nil {
+				return err
+			}
+		}
+
 		log.Infof("Finished to load image %s", filename)
 
 		log.Infof("Creating done stamp file for image %s", filename)

config/schema.go

@@ -55,7 +55,8 @@ var schema = `{
         "sysctl": {"type": "object"},
         "restart_services": {"type": "array"},
 	"hypervisor_service": {"type": "boolean"},
-        "shutdown_timeout": {"type": "integer"}
+        "shutdown_timeout": {"type": "integer"},
+	"preload_wait": {"type": "boolean"}
       }
     },
 

config/types.go

@@ -137,6 +137,7 @@ type RancherConfig struct {
 	RestartServices     []string                                  `yaml:"restart_services,omitempty"`
 	HypervisorService   bool                                      `yaml:"hypervisor_service,omitempty"`
 	ShutdownTimeout     int                                       `yaml:"shutdown_timeout,omitempty"`
+	PreloadWait         bool                                      `yaml:"preload_wait,omitempty"`
 }
 
 type UpgradeConfig struct {

scripts/schema.json

@@ -53,7 +53,8 @@
         "sysctl": {"type": "object"},
         "restart_services": {"type": "array"},
 	"hypervisor_service": {"type": "boolean"},
-	"shutdown_timeout": {"type": "integer"}
+	"shutdown_timeout": {"type": "integer"},
+	"preload_wait": {"type": "boolean"}
       }
     },