diff --git a/graphdriver/devmapper/devmapper.go b/graphdriver/devmapper/devmapper.go
index de82bde0fd..89c36d45ad 100644
--- a/graphdriver/devmapper/devmapper.go
+++ b/graphdriver/devmapper/devmapper.go
@@ -187,7 +187,7 @@ func AttachLoopDevice(filename string) (*osFile, error) {
 }
 
 func getLoopbackBackingFile(file *osFile) (uint64, uint64, error) {
-	dev, inode, err := dmGetLoopbackBackingFile(file.Fd())
+	dev, inode, err := DmGetLoopbackBackingFile(file.Fd())
 	if err != 0 {
 		return 0, 0, ErrGetLoopbackBackingFile
 	}
@@ -195,8 +195,7 @@ func getLoopbackBackingFile(file *osFile) (uint64, uint64, error) {
 }
 
 func LoopbackSetCapacity(file *osFile) error {
-	err := dmLoopbackSetCapacity(file.Fd())
-	if err != 0 {
+	if err := DmLoopbackSetCapacity(file.Fd()); err != 0 {
 		return ErrLoopbackSetCapacity
 	}
 	return nil
diff --git a/graphdriver/devmapper/devmapper_wrapper.go b/graphdriver/devmapper/devmapper_wrapper.go
index 1f28412197..818c968bbf 100644
--- a/graphdriver/devmapper/devmapper_wrapper.go
+++ b/graphdriver/devmapper/devmapper_wrapper.go
@@ -148,26 +148,28 @@ type (
 )
 
 var (
-	DmAttachLoopDevice  = dmAttachLoopDeviceFct
-	DmGetBlockSize      = dmGetBlockSizeFct
-	DmGetLibraryVersion = dmGetLibraryVersionFct
-	DmGetNextTarget     = dmGetNextTargetFct
-	DmLogInitVerbose    = dmLogInitVerboseFct
-	DmSetDevDir         = dmSetDevDirFct
-	DmTaskAddTarget     = dmTaskAddTargetFct
-	DmTaskCreate        = dmTaskCreateFct
-	DmTaskDestroy       = dmTaskDestroyFct
-	DmTaskGetInfo       = dmTaskGetInfoFct
-	DmTaskRun           = dmTaskRunFct
-	DmTaskSetAddNode    = dmTaskSetAddNodeFct
-	DmTaskSetCookie     = dmTaskSetCookieFct
-	DmTaskSetMessage    = dmTaskSetMessageFct
-	DmTaskSetName       = dmTaskSetNameFct
-	DmTaskSetRo         = dmTaskSetRoFct
-	DmTaskSetSector     = dmTaskSetSectorFct
-	DmUdevWait          = dmUdevWaitFct
-	GetBlockSize        = getBlockSizeFct
-	LogWithErrnoInit    = logWithErrnoInitFct
+	DmAttachLoopDevice       = dmAttachLoopDeviceFct
+	DmGetBlockSize           = dmGetBlockSizeFct
+	DmGetLibraryVersion      = dmGetLibraryVersionFct
+	DmGetNextTarget          = dmGetNextTargetFct
+	DmLogInitVerbose         = dmLogInitVerboseFct
+	DmSetDevDir              = dmSetDevDirFct
+	DmTaskAddTarget          = dmTaskAddTargetFct
+	DmTaskCreate             = dmTaskCreateFct
+	DmTaskDestroy            = dmTaskDestroyFct
+	DmTaskGetInfo            = dmTaskGetInfoFct
+	DmTaskRun                = dmTaskRunFct
+	DmTaskSetAddNode         = dmTaskSetAddNodeFct
+	DmTaskSetCookie          = dmTaskSetCookieFct
+	DmTaskSetMessage         = dmTaskSetMessageFct
+	DmTaskSetName            = dmTaskSetNameFct
+	DmTaskSetRo              = dmTaskSetRoFct
+	DmTaskSetSector          = dmTaskSetSectorFct
+	DmUdevWait               = dmUdevWaitFct
+	GetBlockSize             = getBlockSizeFct
+	LogWithErrnoInit         = logWithErrnoInitFct
+	DmGetLoopbackBackingFile = dmGetLoopbackBackingFileFct
+	DmLoopbackSetCapacity    = dmLoopbackSetCapacityFct
 )
 
 func free(p *C.char) {
@@ -238,14 +240,14 @@ func dmTaskAddTargetFct(task *CDmTask,
 		C.uint64_t(start), C.uint64_t(size), Cttype, Cparams))
 }
 
-func dmGetLoopbackBackingFile(fd uintptr) (uint64, uint64, sysErrno) {
+func dmGetLoopbackBackingFileFct(fd uintptr) (uint64, uint64, sysErrno) {
 	var lo64 C.struct_loop_info64
 	_, _, err := sysSyscall(sysSysIoctl, fd, C.LOOP_GET_STATUS64,
 		uintptr(unsafe.Pointer(&lo64)))
 	return uint64(lo64.lo_device), uint64(lo64.lo_inode), sysErrno(err)
 }
 
-func dmLoopbackSetCapacity(fd uintptr) sysErrno {
+func dmLoopbackSetCapacityFct(fd uintptr) sysErrno {
 	_, _, err := sysSyscall(sysSysIoctl, fd, C.LOOP_SET_CAPACITY, 0)
 	return sysErrno(err)
 }
diff --git a/graphdriver/driver.go b/graphdriver/driver.go
index 211806e6c7..e44deb5a69 100644
--- a/graphdriver/driver.go
+++ b/graphdriver/driver.go
@@ -8,8 +8,6 @@ import (
 	"path"
 )
 
-var DefaultDriver string
-
 type InitFunc func(root string) (Driver, error)
 
 type Driver interface {
@@ -34,6 +32,7 @@ type Differ interface {
 }
 
 var (
+	DefaultDriver string
 	// All registred drivers
 	drivers map[string]InitFunc
 	// Slice of drivers that should be used in an order
@@ -64,14 +63,8 @@ func GetDriver(name, home string) (Driver, error) {
 	return nil, fmt.Errorf("No such driver: %s", name)
 }
 
-func New(root string) (Driver, error) {
-	var driver Driver
-	var lastError error
-
-	for _, name := range []string{
-		os.Getenv("DOCKER_DRIVER"),
-		DefaultDriver,
-	} {
+func New(root string) (driver Driver, err error) {
+	for _, name := range []string{os.Getenv("DOCKER_DRIVER"), DefaultDriver} {
 		if name != "" {
 			return GetDriver(name, root)
 		}
@@ -79,9 +72,8 @@ func New(root string) (Driver, error) {
 
 	// Check for priority drivers first
 	for _, name := range priority {
-		driver, lastError = GetDriver(name, root)
-		if lastError != nil {
-			utils.Debugf("Error loading driver %s: %s", name, lastError)
+		if driver, err = GetDriver(name, root); err != nil {
+			utils.Debugf("Error loading driver %s: %s", name, err)
 			continue
 		}
 		return driver, nil
@@ -89,11 +81,10 @@ func New(root string) (Driver, error) {
 
 	// Check all registered drivers if no priority driver is found
 	for _, initFunc := range drivers {
-		driver, lastError = initFunc(root)
-		if lastError != nil {
+		if driver, err = initFunc(root); err != nil {
 			continue
 		}
 		return driver, nil
 	}
-	return nil, lastError
+	return nil, err
 }