Unify rootfs validation

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>

libcontainer/configs/validate/validator.go

@@ -46,6 +46,12 @@ func (v *ConfigValidator) Validate(config *configs.Config) error {
 // rootfs validates if the rootfs is an absolute path and is not a symlink
 // to the container's root filesystem.
 func (v *ConfigValidator) rootfs(config *configs.Config) error {
+	if _, err := os.Stat(config.Rootfs); err != nil {
+		if os.IsNotExist(err) {
+			return fmt.Errorf("rootfs (%s) does not exist", config.Rootfs)
+		}
+		return err
+	}
 	cleaned, err := filepath.Abs(config.Rootfs)
 	if err != nil {
 		return err

utils_linux.go

@@ -179,13 +179,6 @@ func createContainer(context *cli.Context, id string, spec *specs.Spec) (libcont
 		return nil, err
 	}
 
-	if _, err := os.Stat(config.Rootfs); err != nil {
-		if os.IsNotExist(err) {
-			return nil, fmt.Errorf("rootfs (%q) does not exist", config.Rootfs)
-		}
-		return nil, err
-	}
-
 	factory, err := loadFactory(context)
 	if err != nil {
 		return nil, err