Add flag to set default graph driver

Remove the env var DOCKER_DRIVER

config.go

@@ -16,6 +16,7 @@ type DaemonConfig struct {
 	BridgeIface                 string
 	DefaultIp                   net.IP
 	InterContainerCommunication bool
+	GraphDriver                 string
 }
 
 // ConfigFromJob creates and returns a new DaemonConfig object
@@ -37,5 +38,6 @@ func ConfigFromJob(job *engine.Job) *DaemonConfig {
 	}
 	config.DefaultIp = net.ParseIP(job.Getenv("DefaultIp"))
 	config.InterContainerCommunication = job.GetenvBool("InterContainerCommunication")
+	config.GraphDriver = job.Getenv("GraphDriver")
 	return &config
 }

docker/docker.go

@@ -38,6 +38,7 @@ func main() {
 	flEnableIptables := flag.Bool("iptables", true, "Disable iptables within docker")
 	flDefaultIp := flag.String("ip", "0.0.0.0", "Default ip address to use when binding a containers ports")
 	flInterContainerComm := flag.Bool("icc", true, "Enable inter-container communication")
+	flGraphDriver := flag.String("graph-driver", "", "For docker to use a specific graph driver")
 
 	flag.Parse()
 
@@ -82,6 +83,7 @@ func main() {
 		job.Setenv("BridgeIface", *bridgeName)
 		job.Setenv("DefaultIp", *flDefaultIp)
 		job.SetenvBool("InterContainerCommunication", *flInterContainerComm)
+		job.Setenv("GraphDriver", *flGraphDriver)
 		if err := job.Run(); err != nil {
 			log.Fatal(err)
 		}

graphdriver/driver.go

@@ -4,10 +4,11 @@ import (
 	"fmt"
 	"github.com/dotcloud/docker/archive"
 	"github.com/dotcloud/docker/utils"
-	"os"
 	"path"
 )
 
+var DefaultDriver string
+
 type InitFunc func(root string) (Driver, error)
 
 type Driver interface {
@@ -64,9 +65,9 @@ func GetDriver(name, home string) (Driver, error) {
 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)
+
+	if DefaultDriver != "" {
+		return GetDriver(DefaultDriver, root)
 	}
 	// Check for priority drivers first
 	for _, name := range priority {

runtime.go

@@ -637,6 +637,10 @@ func NewRuntime(config *DaemonConfig) (*Runtime, error) {
 }
 
 func NewRuntimeFromDirectory(config *DaemonConfig) (*Runtime, error) {
+
+	// Set the default driver
+	graphdriver.DefaultDriver = config.GraphDriver
+
 	// Load storage driver
 	driver, err := graphdriver.New(config.Root)
 	if err != nil {