devmapper: Fail init with ErrNotSupported if simple devmapper call fails

If we can't even get the current device mapper driver version, then
we cleanly fail the devmapper driver as not supported and fall back
on the next one.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

daemon/graphdriver/devmapper/deviceset.go

@@ -17,6 +17,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/dotcloud/docker/daemon/graphdriver"
 	"github.com/dotcloud/docker/pkg/label"
 	"github.com/dotcloud/docker/utils"
 )
@@ -506,6 +507,12 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 func (devices *DeviceSet) initDevmapper(doInit bool) error {
 	logInit(devices)
 
+	_, err := getDriverVersion()
+	if err != nil {
+		// Can't even get driver version, assume not supported
+		return graphdriver.ErrNotSupported
+	}
+
 	if err := os.MkdirAll(devices.metadataDir(), 0700); err != nil && !os.IsExist(err) {
 		return err
 	}

daemon/graphdriver/devmapper/devmapper.go

@@ -52,6 +52,7 @@ var (
 	ErrTaskAddTarget          = errors.New("dm_task_add_target failed")
 	ErrTaskSetSector          = errors.New("dm_task_set_sector failed")
 	ErrTaskGetInfo            = errors.New("dm_task_get_info failed")
+	ErrTaskGetDriverVersion   = errors.New("dm_task_get_driver_version failed")
 	ErrTaskSetCookie          = errors.New("dm_task_set_cookie failed")
 	ErrNilCookie              = errors.New("cookie ptr can't be nil")
 	ErrAttachLoopbackDevice   = errors.New("loopback mounting failed")
@@ -178,6 +179,14 @@ func (t *Task) GetInfo() (*Info, error) {
 	return info, nil
 }
 
+func (t *Task) GetDriverVersion() (string, error) {
+	res := DmTaskGetDriverVersion(t.unmanaged)
+	if res == "" {
+		return "", ErrTaskGetDriverVersion
+	}
+	return res, nil
+}
+
 func (t *Task) GetNextTarget(next uintptr) (nextPtr uintptr, start uint64,
 	length uint64, targetType string, params string) {
 
@@ -394,6 +403,17 @@ func getInfo(name string) (*Info, error) {
 	return task.GetInfo()
 }
 
+func getDriverVersion() (string, error) {
+	task := TaskCreate(DeviceVersion)
+	if task == nil {
+		return "", fmt.Errorf("Can't create DeviceVersion task")
+	}
+	if err := task.Run(); err != nil {
+		return "", err
+	}
+	return task.GetDriverVersion()
+}
+
 func getStatus(name string) (uint64, uint64, string, string, error) {
 	task, err := createTask(DeviceStatus, name)
 	if task == nil {

daemon/graphdriver/devmapper/devmapper_wrapper.go

@@ -93,6 +93,7 @@ var (
 	DmTaskCreate           = dmTaskCreateFct
 	DmTaskDestroy          = dmTaskDestroyFct
 	DmTaskGetInfo          = dmTaskGetInfoFct
+	DmTaskGetDriverVersion = dmTaskGetDriverVersionFct
 	DmTaskRun              = dmTaskRunFct
 	DmTaskSetAddNode       = dmTaskSetAddNodeFct
 	DmTaskSetCookie        = dmTaskSetCookieFct
@@ -184,6 +185,16 @@ func dmTaskGetInfoFct(task *CDmTask, info *Info) int {
 	return int(C.dm_task_get_info((*C.struct_dm_task)(task), &Cinfo))
 }
 
+func dmTaskGetDriverVersionFct(task *CDmTask) string {
+	buffer := C.malloc(128)
+	defer C.free(buffer)
+	res := C.dm_task_get_driver_version((*C.struct_dm_task)(task), (*C.char)(buffer), 128)
+	if res == 0 {
+		return ""
+	}
+	return C.GoString((*C.char)(buffer))
+}
+
 func dmGetNextTargetFct(task *CDmTask, next uintptr, start, length *uint64, target, params *string) uintptr {
 	var (
 		Cstart, Clength      C.uint64_t