From 8c21d2acd33c2bbaba224e19fbef30a3ba8788df Mon Sep 17 00:00:00 2001
From: Solomon Hykes <solomon@dotcloud.com>
Date: Fri, 8 Nov 2013 02:49:32 +0000
Subject: [PATCH] Set DOCKER_DRIVER to override the choice of driver (aufs,
 devicemapper or dummy)

---
 graphdriver/driver.go | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/graphdriver/driver.go b/graphdriver/driver.go
index 1f777ccde7..bebbf02d3d 100644
--- a/graphdriver/driver.go
+++ b/graphdriver/driver.go
@@ -3,6 +3,7 @@ package graphdriver
 import (
 	"fmt"
 	"github.com/dotcloud/docker/archive"
+	"os"
 )
 
 
@@ -45,18 +46,27 @@ func Register(name string, initFunc InitFunc) error {
 	return nil
 }
 
+func getDriver(name, home string) (Driver, error) {
+	if initFunc, exists := drivers[name]; exists {
+		return initFunc(home)
+	}
+	return nil, fmt.Errorf("No such driver: %s", name)
+}
+
 func New(root string) (Driver, error) {
 	var driver Driver
 	var lastError error
+	// Use environment variable DOCKER_DRIVER to force a choice of driver
+	if name := os.Getenv("DOCKER_DRIVER"); name != "" {
+		return getDriver(name, root)
+	}
 	// Check for priority drivers first
 	for _, name := range priority {
-		if initFunc, exists := drivers[name]; exists {
-			driver, lastError = initFunc(root)
-			if lastError != nil {
-				continue
-			}
-			return driver, nil
+		driver, lastError = getDriver(name, root)
+		if lastError != nil {
+			continue
 		}
+		return driver, nil
 	}
 
 	// Check all registered drivers if no priority driver is found