@@ -394,6 +394,50 @@ func (devices *DeviceSet) initMetaData() error {

 	return nil

 }

+func (devices *DeviceSet) incNextDeviceId() {

+	// Ids are 24bit, so wrap around

+	devices.NextDeviceId = (devices.NextDeviceId + 1) & 0xffffff

+}

+

+func (devices *DeviceSet) createDevice(deviceId *int) error {

+	for {

+		if err := devicemapper.CreateDevice(devices.getPoolDevName(), *deviceId); err != nil {

+			if devicemapper.DeviceIdExists(err) {

+				// Device Id already exists. Try a new one.

+				devices.incNextDeviceId()

+				*deviceId = devices.NextDeviceId

+				continue

+			}

+			log.Debugf("Error creating device: %s", err)

+			return err

+		}

+		break

+	}

+	devices.incNextDeviceId()

+	return nil

+}

+

+func (devices *DeviceSet) createSnapDevice(baseInfo *DevInfo, deviceId *int) error {

+	log.Debugf("[deviceset] createSnapDevice() DeviceId=%d", *deviceId)

+	defer log.Debugf("[deviceset] createSnapDevice() END DeviceId=%d", *deviceId)

+

+	for {

+		if err := devicemapper.CreateSnapDevice(devices.getPoolDevName(), *deviceId, baseInfo.Name(), baseInfo.DeviceId); err != nil {

+			if devicemapper.DeviceIdExists(err) {

+				// Device Id already exists. Try a new one.

+				devices.incNextDeviceId()

+				*deviceId = devices.NextDeviceId

+				continue

+			}

+			log.Debugf("Error creating snap device: %s", err)

+			return err

+		}

+		break

+	}

+	devices.incNextDeviceId()

+	return nil

+}

+

 func (devices *DeviceSet) loadMetadata(hash string) *DevInfo {

 	info := &DevInfo{Hash: hash, devices: devices}

@@ -439,20 +483,16 @@ func (devices *DeviceSet) setupBaseImage() error {

 	log.Debugf("Initializing base device-mapper thin volume")

-	id := devices.NextDeviceId

-

 	// Create initial device

-	if err := devicemapper.CreateDevice(devices.getPoolDevName(), &id); err != nil {

+	deviceId := devices.NextDeviceId

+	if err := devices.createDevice(&deviceId); err != nil {

 		return err

 	}

-	// Ids are 24bit, so wrap around

-	devices.NextDeviceId = (id + 1) & 0xffffff

-

-	log.Debugf("Registering base device (id %v) with FS size %v", id, devices.baseFsSize)

-	info, err := devices.registerDevice(id, "", devices.baseFsSize)

+	log.Debugf("Registering base device (id %v) with FS size %v", deviceId, devices.baseFsSize)

+	info, err := devices.registerDevice(deviceId, "", devices.baseFsSize)

 	if err != nil {

-		_ = devicemapper.DeleteDevice(devices.getPoolDevName(), id)

+		_ = devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

 		return err

 	}

@@ -751,6 +791,9 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {

 }

 func (devices *DeviceSet) AddDevice(hash, baseHash string) error {

+	log.Debugf("[deviceset] AddDevice() hash=%s basehash=%s", hash, baseHash)

+	defer log.Debugf("[deviceset] AddDevice END")

+

 	baseInfo, err := devices.lookupDevice(baseHash)

 	if err != nil {

 		return err

@@ -767,15 +810,11 @@ func (devices *DeviceSet) AddDevice(hash, baseHash string) error {

 	}

 	deviceId := devices.NextDeviceId

-

-	if err := devicemapper.CreateSnapDevice(devices.getPoolDevName(), &deviceId, baseInfo.Name(), baseInfo.DeviceId); err != nil {

+	if err := devices.createSnapDevice(baseInfo, &deviceId); err != nil {

 		log.Debugf("Error creating snap device: %s", err)

 		return err

 	}

-	// Ids are 24bit, so wrap around

-	devices.NextDeviceId = (deviceId + 1) & 0xffffff

-

 	if _, err := devices.registerDevice(deviceId, hash, baseInfo.Size); err != nil {

 		devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

 		log.Debugf("Error registering device: %s", err)

@@ -67,6 +67,7 @@ var (

 	ErrGetLoopbackBackingFile = errors.New("Unable to get loopback backing file")

 	ErrLoopbackSetCapacity    = errors.New("Unable set loopback capacity")

 	ErrBusy                   = errors.New("Device is Busy")

+	ErrDeviceIdExists         = errors.New("Device Id Exists")

 	dmSawBusy  bool

 	dmSawExist bool

@@ -97,6 +98,16 @@ type (

 	AddNodeType int

 )

+// Returns whether error conveys the information about device Id already

+// exist or not. This will be true if device creation or snap creation

+// operation fails if device or snap device already exists in pool.

+// Current implementation is little crude as it scans the error string

+// for exact pattern match. Replacing it with more robust implementation

+// is desirable.

+func DeviceIdExists(err error) bool {

+	return fmt.Sprint(err) == fmt.Sprint(ErrDeviceIdExists)

+}

+

 func (t *Task) destroy() {

 	if t != nil {

 		DmTaskDestroy(t.unmanaged)

@@ -528,33 +539,29 @@ func ResumeDevice(name string) error {

 	return nil

 }

-func CreateDevice(poolName string, deviceId *int) error {

-	log.Debugf("[devmapper] CreateDevice(poolName=%v, deviceId=%v)", poolName, *deviceId)

-

-	for {

-		task, err := TaskCreateNamed(DeviceTargetMsg, poolName)

-		if task == nil {

-			return err

-		}

+func CreateDevice(poolName string, deviceId int) error {

+	log.Debugf("[devmapper] CreateDevice(poolName=%v, deviceId=%v)", poolName, deviceId)

+	task, err := TaskCreateNamed(DeviceTargetMsg, poolName)

+	if task == nil {

+		return err

+	}

-		if err := task.SetSector(0); err != nil {

-			return fmt.Errorf("Can't set sector %s", err)

-		}

+	if err := task.SetSector(0); err != nil {

+		return fmt.Errorf("Can't set sector %s", err)

+	}

-		if err := task.SetMessage(fmt.Sprintf("create_thin %d", *deviceId)); err != nil {

-			return fmt.Errorf("Can't set message %s", err)

-		}

+	if err := task.SetMessage(fmt.Sprintf("create_thin %d", deviceId)); err != nil {

+		return fmt.Errorf("Can't set message %s", err)

+	}

-		dmSawExist = false // reset before the task is run

-		if err := task.Run(); err != nil {

-			if dmSawExist {

-				// Already exists, try next id

-				*deviceId++

-				continue

-			}

+	dmSawExist = false // reset before the task is run

+	if err := task.Run(); err != nil {

+		// Caller wants to know about ErrDeviceIdExists so that it can try with a different device id.

+		if dmSawExist {

+			return ErrDeviceIdExists

+		} else {

 			return fmt.Errorf("Error running CreateDevice %s", err)

 		}

-		break

 	}

 	return nil

 }

@@ -607,7 +614,7 @@ func ActivateDevice(poolName string, name string, deviceId int, size uint64) err

 	return nil

 }

-func CreateSnapDevice(poolName string, deviceId *int, baseName string, baseDeviceId int) error {

+func CreateSnapDevice(poolName string, deviceId int, baseName string, baseDeviceId int) error {

 	devinfo, _ := GetInfo(baseName)

 	doSuspend := devinfo != nil && devinfo.Exists != 0

@@ -617,44 +624,39 @@ func CreateSnapDevice(poolName string, deviceId *int, baseName string, baseDevic

 		}

 	}

-	for {

-		task, err := TaskCreateNamed(DeviceTargetMsg, poolName)

-		if task == nil {

-			if doSuspend {

-				ResumeDevice(baseName)

-			}

-			return err

+	task, err := TaskCreateNamed(DeviceTargetMsg, poolName)

+	if task == nil {

+		if doSuspend {

+			ResumeDevice(baseName)

 		}

+		return err

+	}

-		if err := task.SetSector(0); err != nil {

-			if doSuspend {

-				ResumeDevice(baseName)

-			}

-			return fmt.Errorf("Can't set sector %s", err)

+	if err := task.SetSector(0); err != nil {

+		if doSuspend {

+			ResumeDevice(baseName)

 		}

+		return fmt.Errorf("Can't set sector %s", err)

+	}

-		if err := task.SetMessage(fmt.Sprintf("create_snap %d %d", *deviceId, baseDeviceId)); err != nil {

-			if doSuspend {

-				ResumeDevice(baseName)

-			}

-			return fmt.Errorf("Can't set message %s", err)

+	if err := task.SetMessage(fmt.Sprintf("create_snap %d %d", deviceId, baseDeviceId)); err != nil {

+		if doSuspend {

+			ResumeDevice(baseName)

 		}

+		return fmt.Errorf("Can't set message %s", err)

+	}

-		dmSawExist = false // reset before the task is run

-		if err := task.Run(); err != nil {

-			if dmSawExist {

-				// Already exists, try next id

-				*deviceId++

-				continue

-			}

-

-			if doSuspend {

-				ResumeDevice(baseName)

-			}

+	dmSawExist = false // reset before the task is run

+	if err := task.Run(); err != nil {

+		if doSuspend {

+			ResumeDevice(baseName)

+		}

+		// Caller wants to know about ErrDeviceIdExists so that it can try with a different device id.

+		if dmSawExist {

+			return ErrDeviceIdExists

+		} else {

 			return fmt.Errorf("Error running DeviceCreate (createSnapDevice) %s", err)

 		}

-

-		break

 	}

 	if doSuspend {