diff --git a/distribution/xfer/download.go b/distribution/xfer/download.go
index 6eddfac0dd..af1a3995d2 100644
--- a/distribution/xfer/download.go
+++ b/distribution/xfer/download.go
@@ -23,21 +23,21 @@ const maxDownloadAttempts = 5
 // layers.
 type LayerDownloadManager struct {
 	layerStore          layer.Store
-	tm                  TransferManager
+	tm                  *transferManager
 	waitDuration        time.Duration
 	maxDownloadAttempts int
 }
 
 // SetConcurrency sets the max concurrent downloads for each pull
 func (ldm *LayerDownloadManager) SetConcurrency(concurrency int) {
-	ldm.tm.SetConcurrency(concurrency)
+	ldm.tm.setConcurrency(concurrency)
 }
 
 // NewLayerDownloadManager returns a new LayerDownloadManager.
-func NewLayerDownloadManager(layerStore layer.Store, concurrencyLimit int, options ...func(*LayerDownloadManager)) *LayerDownloadManager {
+func NewLayerDownloadManager(layerStore layer.Store, concurrencyLimit int, options ...DownloadOption) *LayerDownloadManager {
 	manager := LayerDownloadManager{
 		layerStore:          layerStore,
-		tm:                  NewTransferManager(concurrencyLimit),
+		tm:                  newTransferManager(concurrencyLimit),
 		waitDuration:        time.Second,
 		maxDownloadAttempts: maxDownloadAttempts,
 	}
@@ -47,16 +47,19 @@ func NewLayerDownloadManager(layerStore layer.Store, concurrencyLimit int, optio
 	return &manager
 }
 
+// DownloadOption set options for the LayerDownloadManager.
+type DownloadOption func(*LayerDownloadManager)
+
 // WithMaxDownloadAttempts configures the maximum number of download
 // attempts for a download manager.
-func WithMaxDownloadAttempts(max int) func(*LayerDownloadManager) {
+func WithMaxDownloadAttempts(max int) DownloadOption {
 	return func(dlm *LayerDownloadManager) {
 		dlm.maxDownloadAttempts = max
 	}
 }
 
 type downloadTransfer struct {
-	Transfer
+	transfer
 
 	layerStore layer.Store
 	layer      layer.Layer
@@ -87,13 +90,17 @@ type DownloadDescriptor interface {
 	Close()
 }
 
-// DownloadDescriptorWithRegistered is a DownloadDescriptor that has an
-// additional Registered method which gets called after a downloaded layer is
-// registered. This allows the user of the download manager to know the DiffID
-// of each registered layer. This method is called if a cast to
-// DownloadDescriptorWithRegistered is successful.
-type DownloadDescriptorWithRegistered interface {
-	DownloadDescriptor
+// DigestRegisterer can be implemented by a DownloadDescriptor, and provides a
+// Registered method which gets called after a downloaded layer is registered.
+// This allows the user of the download manager to know the DiffID of each
+// registered layer. This method is called if a cast to DigestRegisterer is
+// successful.
+type DigestRegisterer interface {
+
+	// TODO existing implementations in distribution and builder-next swallow errors
+	// when registering the diffID. Consider changing the Registered signature
+	// to return the error.
+
 	Registered(diffID layer.DiffID)
 }
 
@@ -108,7 +115,7 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 	var (
 		topLayer       layer.Layer
 		topDownload    *downloadTransfer
-		watcher        *Watcher
+		watcher        *watcher
 		missingLayer   bool
 		transferKey    = ""
 		downloadsByKey = make(map[string]*downloadTransfer)
@@ -137,8 +144,7 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 					missingLayer = false
 					rootFS.Append(diffID)
 					// Register this repository as a source of this layer.
-					withRegistered, hasRegistered := descriptor.(DownloadDescriptorWithRegistered)
-					if hasRegistered { // As layerstore may set the driver
+					if withRegistered, ok := descriptor.(DigestRegisterer); ok { // As layerstore may set the driver
 						withRegistered.Registered(diffID)
 					}
 					continue
@@ -148,11 +154,11 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 
 		// Does this layer have the same data as a previous layer in
 		// the stack? If so, avoid downloading it more than once.
-		var topDownloadUncasted Transfer
+		var topDownloadUncasted transfer
 		if existingDownload, ok := downloadsByKey[key]; ok {
 			xferFunc := ldm.makeDownloadFuncFromDownload(descriptor, existingDownload, topDownload)
-			defer topDownload.Transfer.Release(watcher)
-			topDownloadUncasted, watcher = ldm.tm.Transfer(transferKey, xferFunc, progressOutput)
+			defer topDownload.transfer.release(watcher)
+			topDownloadUncasted, watcher = ldm.tm.transfer(transferKey, xferFunc, progressOutput)
 			topDownload = topDownloadUncasted.(*downloadTransfer)
 			continue
 		}
@@ -160,14 +166,14 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 		// Layer is not known to exist - download and register it.
 		progress.Update(progressOutput, descriptor.ID(), "Pulling fs layer")
 
-		var xferFunc DoFunc
+		var xferFunc doFunc
 		if topDownload != nil {
 			xferFunc = ldm.makeDownloadFunc(descriptor, "", topDownload)
-			defer topDownload.Transfer.Release(watcher)
+			defer topDownload.transfer.release(watcher)
 		} else {
 			xferFunc = ldm.makeDownloadFunc(descriptor, rootFS.ChainID(), nil)
 		}
-		topDownloadUncasted, watcher = ldm.tm.Transfer(transferKey, xferFunc, progressOutput)
+		topDownloadUncasted, watcher = ldm.tm.transfer(transferKey, xferFunc, progressOutput)
 		topDownload = topDownloadUncasted.(*downloadTransfer)
 		downloadsByKey[key] = topDownload
 	}
@@ -192,15 +198,15 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 
 	select {
 	case <-ctx.Done():
-		topDownload.Transfer.Release(watcher)
+		topDownload.transfer.release(watcher)
 		return rootFS, func() {}, ctx.Err()
-	case <-topDownload.Done():
+	case <-topDownload.done():
 		break
 	}
 
 	l, err := topDownload.result()
 	if err != nil {
-		topDownload.Transfer.Release(watcher)
+		topDownload.transfer.release(watcher)
 		return rootFS, func() {}, err
 	}
 
@@ -208,13 +214,13 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 	// base layer on Windows.
 	for range layers {
 		if l == nil {
-			topDownload.Transfer.Release(watcher)
+			topDownload.transfer.release(watcher)
 			return rootFS, func() {}, errors.New("internal error: too few parent layers")
 		}
 		rootFS.DiffIDs = append([]layer.DiffID{l.DiffID()}, rootFS.DiffIDs...)
 		l = l.Parent()
 	}
-	return rootFS, func() { topDownload.Transfer.Release(watcher) }, err
+	return rootFS, func() { topDownload.transfer.release(watcher) }, err
 }
 
 // makeDownloadFunc returns a function that performs the layer download and
@@ -222,10 +228,10 @@ func (ldm *LayerDownloadManager) Download(ctx context.Context, initialRootFS ima
 // complete before the registration step, and registers the downloaded data
 // on top of parentDownload's resulting layer. Otherwise, it registers the
 // layer on top of the ChainID given by parentLayer.
-func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor, parentLayer layer.ChainID, parentDownload *downloadTransfer) DoFunc {
-	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer {
+func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor, parentLayer layer.ChainID, parentDownload *downloadTransfer) doFunc {
+	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) transfer {
 		d := &downloadTransfer{
-			Transfer:   NewTransfer(),
+			transfer:   newTransfer(),
 			layerStore: ldm.layerStore,
 		}
 
@@ -247,7 +253,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 				// Did the parent download already fail or get
 				// cancelled?
 				select {
-				case <-parentDownload.Done():
+				case <-parentDownload.done():
 					_, err := parentDownload.result()
 					if err != nil {
 						d.err = err
@@ -267,7 +273,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 			defer descriptor.Close()
 
 			for {
-				downloadReader, size, err = descriptor.Download(d.Transfer.Context(), progressOutput)
+				downloadReader, size, err = descriptor.Download(d.transfer.context(), progressOutput)
 				if err == nil {
 					break
 				}
@@ -275,7 +281,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 				// If an error was returned because the context
 				// was cancelled, we shouldn't retry.
 				select {
-				case <-d.Transfer.Context().Done():
+				case <-d.transfer.context().Done():
 					d.err = err
 					return
 				default:
@@ -302,7 +308,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 							ticker.Stop()
 							break selectLoop
 						}
-					case <-d.Transfer.Context().Done():
+					case <-d.transfer.context().Done():
 						ticker.Stop()
 						d.err = errors.New("download cancelled during retry delay")
 						return
@@ -315,11 +321,11 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 
 			if parentDownload != nil {
 				select {
-				case <-d.Transfer.Context().Done():
+				case <-d.transfer.context().Done():
 					d.err = errors.New("layer registration cancelled")
 					downloadReader.Close()
 					return
-				case <-parentDownload.Done():
+				case <-parentDownload.done():
 				}
 
 				l, err := parentDownload.result()
@@ -331,7 +337,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 				parentLayer = l.ChainID()
 			}
 
-			reader := progress.NewProgressReader(ioutils.NewCancelReadCloser(d.Transfer.Context(), downloadReader), progressOutput, size, descriptor.ID(), "Extracting")
+			reader := progress.NewProgressReader(ioutils.NewCancelReadCloser(d.transfer.context(), downloadReader), progressOutput, size, descriptor.ID(), "Extracting")
 			defer reader.Close()
 
 			inflatedLayerData, err := archive.DecompressStream(reader)
@@ -351,7 +357,7 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 			}
 			if err != nil {
 				select {
-				case <-d.Transfer.Context().Done():
+				case <-d.transfer.context().Done():
 					d.err = errors.New("layer registration cancelled")
 				default:
 					d.err = fmt.Errorf("failed to register layer: %v", err)
@@ -360,15 +366,15 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 			}
 
 			progress.Update(progressOutput, descriptor.ID(), "Pull complete")
-			withRegistered, hasRegistered := descriptor.(DownloadDescriptorWithRegistered)
-			if hasRegistered {
+
+			if withRegistered, ok := descriptor.(DigestRegisterer); ok {
 				withRegistered.Registered(d.layer.DiffID())
 			}
 
 			// Doesn't actually need to be its own goroutine, but
 			// done like this so we can defer close(c).
 			go func() {
-				<-d.Transfer.Released()
+				<-d.transfer.released()
 				if d.layer != nil {
 					layer.ReleaseAndLog(d.layerStore, d.layer)
 				}
@@ -386,10 +392,10 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,
 // parentDownload. This function does not log progress output because it would
 // interfere with the progress reporting for sourceDownload, which has the same
 // Key.
-func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor DownloadDescriptor, sourceDownload *downloadTransfer, parentDownload *downloadTransfer) DoFunc {
-	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer {
+func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor DownloadDescriptor, sourceDownload *downloadTransfer, parentDownload *downloadTransfer) doFunc {
+	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) transfer {
 		d := &downloadTransfer{
-			Transfer:   NewTransfer(),
+			transfer:   newTransfer(),
 			layerStore: ldm.layerStore,
 		}
 
@@ -403,10 +409,10 @@ func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor Downloa
 			close(inactive)
 
 			select {
-			case <-d.Transfer.Context().Done():
+			case <-d.transfer.context().Done():
 				d.err = errors.New("layer registration cancelled")
 				return
-			case <-parentDownload.Done():
+			case <-parentDownload.done():
 			}
 
 			l, err := parentDownload.result()
@@ -420,10 +426,10 @@ func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor Downloa
 			// parentDownload finished, but wait for it explicitly
 			// to be sure.
 			select {
-			case <-d.Transfer.Context().Done():
+			case <-d.transfer.context().Done():
 				d.err = errors.New("layer registration cancelled")
 				return
-			case <-sourceDownload.Done():
+			case <-sourceDownload.done():
 			}
 
 			l, err = sourceDownload.result()
@@ -453,15 +459,14 @@ func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor Downloa
 				return
 			}
 
-			withRegistered, hasRegistered := descriptor.(DownloadDescriptorWithRegistered)
-			if hasRegistered {
+			if withRegistered, ok := descriptor.(DigestRegisterer); ok {
 				withRegistered.Registered(d.layer.DiffID())
 			}
 
 			// Doesn't actually need to be its own goroutine, but
 			// done like this so we can defer close(c).
 			go func() {
-				<-d.Transfer.Released()
+				<-d.transfer.released()
 				if d.layer != nil {
 					layer.ReleaseAndLog(d.layerStore, d.layer)
 				}
diff --git a/distribution/xfer/transfer.go b/distribution/xfer/transfer.go
index 82df793ebe..d5f96c8aea 100644
--- a/distribution/xfer/transfer.go
+++ b/distribution/xfer/transfer.go
@@ -19,8 +19,8 @@ func (e DoNotRetry) Error() string {
 	return e.Err.Error()
 }
 
-// Watcher is returned by Watch and can be passed to Release to stop watching.
-type Watcher struct {
+// watcher is returned by Watch and can be passed to Release to stop watching.
+type watcher struct {
 	// signalChan is used to signal to the watcher goroutine that
 	// new progress information is available, or that the transfer
 	// has finished.
@@ -34,18 +34,18 @@ type Watcher struct {
 	running chan struct{}
 }
 
-// Transfer represents an in-progress transfer.
-type Transfer interface {
-	Watch(progressOutput progress.Output) *Watcher
-	Release(*Watcher)
-	Context() context.Context
-	Close()
-	Done() <-chan struct{}
-	Released() <-chan struct{}
-	Broadcast(mainProgressChan <-chan progress.Progress)
+// transfer represents an in-progress transfer.
+type transfer interface {
+	watch(progressOutput progress.Output) *watcher
+	release(*watcher)
+	context() context.Context
+	close()
+	done() <-chan struct{}
+	released() <-chan struct{}
+	broadcast(mainProgressChan <-chan progress.Progress)
 }
 
-type transfer struct {
+type xfer struct {
 	mu sync.Mutex
 
 	ctx    context.Context
@@ -53,7 +53,7 @@ type transfer struct {
 
 	// watchers keeps track of the goroutines monitoring progress output,
 	// indexed by the channels that release them.
-	watchers map[chan struct{}]*Watcher
+	watchers map[chan struct{}]*watcher
 
 	// lastProgress is the most recently received progress event.
 	lastProgress progress.Progress
@@ -62,9 +62,9 @@ type transfer struct {
 
 	// running remains open as long as the transfer is in progress.
 	running chan struct{}
-	// released stays open until all watchers release the transfer and
-	// the transfer is no longer tracked by the transfer manager.
-	released chan struct{}
+	// releasedChan stays open until all watchers release the transfer and
+	// the transfer is no longer tracked by the transferManager.
+	releasedChan chan struct{}
 
 	// broadcastDone is true if the main progress channel has closed.
 	broadcastDone bool
@@ -77,12 +77,12 @@ type transfer struct {
 	broadcastSyncChan chan struct{}
 }
 
-// NewTransfer creates a new transfer.
-func NewTransfer() Transfer {
-	t := &transfer{
-		watchers:          make(map[chan struct{}]*Watcher),
+// newTransfer creates a new transfer.
+func newTransfer() transfer {
+	t := &xfer{
+		watchers:          make(map[chan struct{}]*watcher),
 		running:           make(chan struct{}),
-		released:          make(chan struct{}),
+		releasedChan:      make(chan struct{}),
 		broadcastSyncChan: make(chan struct{}),
 	}
 
@@ -95,7 +95,7 @@ func NewTransfer() Transfer {
 }
 
 // Broadcast copies the progress and error output to all viewers.
-func (t *transfer) Broadcast(mainProgressChan <-chan progress.Progress) {
+func (t *xfer) broadcast(mainProgressChan <-chan progress.Progress) {
 	for {
 		var (
 			p  progress.Progress
@@ -137,11 +137,11 @@ func (t *transfer) Broadcast(mainProgressChan <-chan progress.Progress) {
 
 // Watch adds a watcher to the transfer. The supplied channel gets progress
 // updates and is closed when the transfer finishes.
-func (t *transfer) Watch(progressOutput progress.Output) *Watcher {
+func (t *xfer) watch(progressOutput progress.Output) *watcher {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 
-	w := &Watcher{
+	w := &watcher{
 		releaseChan: make(chan struct{}),
 		signalChan:  make(chan struct{}),
 		running:     make(chan struct{}),
@@ -205,7 +205,7 @@ func (t *transfer) Watch(progressOutput progress.Output) *Watcher {
 // to be notified about the progress of the transfer. All calls to Watch must
 // be paired with later calls to Release so that the lifecycle of the transfer
 // is properly managed.
-func (t *transfer) Release(watcher *Watcher) {
+func (t *xfer) release(watcher *watcher) {
 	t.mu.Lock()
 	delete(t.watchers, watcher.releaseChan)
 
@@ -216,9 +216,9 @@ func (t *transfer) Release(watcher *Watcher) {
 			// while waiting for a previous watcher goroutine to
 			// finish.
 			select {
-			case <-t.released:
+			case <-t.releasedChan:
 			default:
-				close(t.released)
+				close(t.releasedChan)
 			}
 		} else {
 			t.cancel()
@@ -233,7 +233,7 @@ func (t *transfer) Release(watcher *Watcher) {
 
 // Done returns a channel which is closed if the transfer completes or is
 // cancelled. Note that having 0 watchers causes a transfer to be cancelled.
-func (t *transfer) Done() <-chan struct{} {
+func (t *xfer) done() <-chan struct{} {
 	// Note that this doesn't return t.ctx.Done() because that channel will
 	// be closed the moment Cancel is called, and we need to return a
 	// channel that blocks until a cancellation is actually acknowledged by
@@ -242,75 +242,66 @@ func (t *transfer) Done() <-chan struct{} {
 }
 
 // Released returns a channel which is closed once all watchers release the
-// transfer AND the transfer is no longer tracked by the transfer manager.
-func (t *transfer) Released() <-chan struct{} {
-	return t.released
+// transfer AND the transfer is no longer tracked by the transferManager.
+func (t *xfer) released() <-chan struct{} {
+	return t.releasedChan
 }
 
 // Context returns the context associated with the transfer.
-func (t *transfer) Context() context.Context {
+func (t *xfer) context() context.Context {
 	return t.ctx
 }
 
-// Close is called by the transfer manager when the transfer is no longer
+// Close is called by the transferManager when the transfer is no longer
 // being tracked.
-func (t *transfer) Close() {
+func (t *xfer) close() {
 	t.mu.Lock()
 	t.closed = true
 	if len(t.watchers) == 0 {
-		close(t.released)
+		close(t.releasedChan)
 	}
 	t.mu.Unlock()
 }
 
-// DoFunc is a function called by the transfer manager to actually perform
+// doFunc is a function called by the transferManager to actually perform
 // a transfer. It should be non-blocking. It should wait until the start channel
 // is closed before transferring any data. If the function closes inactive, that
-// signals to the transfer manager that the job is no longer actively moving
+// signals to the transferManager that the job is no longer actively moving
 // data - for example, it may be waiting for a dependent transfer to finish.
 // This prevents it from taking up a slot.
-type DoFunc func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer
-
-// TransferManager is used by LayerDownloadManager and LayerUploadManager to
-// schedule and deduplicate transfers. It is up to the TransferManager
-// implementation to make the scheduling and concurrency decisions.
-type TransferManager interface {
-	// Transfer checks if a transfer with the given key is in progress. If
-	// so, it returns progress and error output from that transfer.
-	// Otherwise, it will call xferFunc to initiate the transfer.
-	Transfer(key string, xferFunc DoFunc, progressOutput progress.Output) (Transfer, *Watcher)
-	// SetConcurrency set the concurrencyLimit so that it is adjustable daemon reload
-	SetConcurrency(concurrency int)
-}
+type doFunc func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) transfer
 
+// transferManager is used by LayerDownloadManager and LayerUploadManager to
+// schedule and deduplicate transfers. It is up to the transferManager
+// to make the scheduling and concurrency decisions.
 type transferManager struct {
 	mu sync.Mutex
 
 	concurrencyLimit int
 	activeTransfers  int
-	transfers        map[string]Transfer
+	transfers        map[string]transfer
 	waitingTransfers []chan struct{}
 }
 
-// NewTransferManager returns a new TransferManager.
-func NewTransferManager(concurrencyLimit int) TransferManager {
+// newTransferManager returns a new transferManager.
+func newTransferManager(concurrencyLimit int) *transferManager {
 	return &transferManager{
 		concurrencyLimit: concurrencyLimit,
-		transfers:        make(map[string]Transfer),
+		transfers:        make(map[string]transfer),
 	}
 }
 
-// SetConcurrency sets the concurrencyLimit
-func (tm *transferManager) SetConcurrency(concurrency int) {
+// setConcurrency sets the concurrencyLimit
+func (tm *transferManager) setConcurrency(concurrency int) {
 	tm.mu.Lock()
 	tm.concurrencyLimit = concurrency
 	tm.mu.Unlock()
 }
 
-// Transfer checks if a transfer matching the given key is in progress. If not,
+// transfer checks if a transfer matching the given key is in progress. If not,
 // it starts one by calling xferFunc. The caller supplies a channel which
 // receives progress output from the transfer.
-func (tm *transferManager) Transfer(key string, xferFunc DoFunc, progressOutput progress.Output) (Transfer, *Watcher) {
+func (tm *transferManager) transfer(key string, xferFunc doFunc, progressOutput progress.Output) (transfer, *watcher) {
 	tm.mu.Lock()
 	defer tm.mu.Unlock()
 
@@ -319,24 +310,24 @@ func (tm *transferManager) Transfer(key string, xferFunc DoFunc, progressOutput
 		if !present {
 			break
 		}
-		// Transfer is already in progress.
-		watcher := xfer.Watch(progressOutput)
+		// transfer is already in progress.
+		watcher := xfer.watch(progressOutput)
 
 		select {
-		case <-xfer.Context().Done():
+		case <-xfer.context().Done():
 			// We don't want to watch a transfer that has been cancelled.
 			// Wait for it to be removed from the map and try again.
-			xfer.Release(watcher)
+			xfer.release(watcher)
 			tm.mu.Unlock()
 			// The goroutine that removes this transfer from the
 			// map is also waiting for xfer.Done(), so yield to it.
 			// This could be avoided by adding a Closed method
-			// to Transfer to allow explicitly waiting for it to be
+			// to transfer to allow explicitly waiting for it to be
 			// removed the map, but forcing a scheduling round in
 			// this very rare case seems better than bloating the
 			// interface definition.
 			runtime.Gosched()
-			<-xfer.Done()
+			<-xfer.done()
 			tm.mu.Lock()
 		default:
 			return xfer, watcher
@@ -355,8 +346,8 @@ func (tm *transferManager) Transfer(key string, xferFunc DoFunc, progressOutput
 
 	mainProgressChan := make(chan progress.Progress)
 	xfer := xferFunc(mainProgressChan, start, inactive)
-	watcher := xfer.Watch(progressOutput)
-	go xfer.Broadcast(mainProgressChan)
+	watcher := xfer.watch(progressOutput)
+	go xfer.broadcast(mainProgressChan)
 	tm.transfers[key] = xfer
 
 	// When the transfer is finished, remove from the map.
@@ -368,14 +359,14 @@ func (tm *transferManager) Transfer(key string, xferFunc DoFunc, progressOutput
 				tm.inactivate(start)
 				tm.mu.Unlock()
 				inactive = nil
-			case <-xfer.Done():
+			case <-xfer.done():
 				tm.mu.Lock()
 				if inactive != nil {
 					tm.inactivate(start)
 				}
 				delete(tm.transfers, key)
 				tm.mu.Unlock()
-				xfer.Close()
+				xfer.close()
 				return
 			}
 		}
diff --git a/distribution/xfer/transfer_test.go b/distribution/xfer/transfer_test.go
index f8f8e96fe0..305bb91662 100644
--- a/distribution/xfer/transfer_test.go
+++ b/distribution/xfer/transfer_test.go
@@ -9,15 +9,15 @@ import (
 )
 
 func TestTransfer(t *testing.T) {
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) Transfer {
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) transfer {
 			select {
 			case <-start:
 			default:
 				t.Errorf("%s: transfer function not started even though concurrency limit not reached", id)
 			}
 
-			xfer := NewTransfer()
+			xfer := newTransfer()
 			go func() {
 				for i := 0; i <= 10; i++ {
 					progressChan <- progress.Progress{ID: id, Action: "testing", Current: int64(i), Total: 10}
@@ -29,7 +29,7 @@ func TestTransfer(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(5)
+	tm := newTransferManager(5)
 	progressChan := make(chan progress.Progress)
 	progressDone := make(chan struct{})
 	receivedProgress := make(map[string]int64)
@@ -47,15 +47,15 @@ func TestTransfer(t *testing.T) {
 
 	// Start a few transfers
 	ids := []string{"id1", "id2", "id3"}
-	xfers := make([]Transfer, len(ids))
-	watchers := make([]*Watcher, len(ids))
+	xfers := make([]transfer, len(ids))
+	watchers := make([]*watcher, len(ids))
 	for i, id := range ids {
-		xfers[i], watchers[i] = tm.Transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
+		xfers[i], watchers[i] = tm.transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
 	}
 
 	for i, xfer := range xfers {
-		<-xfer.Done()
-		xfer.Release(watchers[i])
+		<-xfer.done()
+		xfer.release(watchers[i])
 	}
 	close(progressChan)
 	<-progressDone
@@ -68,12 +68,12 @@ func TestTransfer(t *testing.T) {
 }
 
 func TestConcurrencyLimit(t *testing.T) {
-	concurrencyLimit := 3
+	const concurrencyLimit = 3
 	var runningJobs int32
 
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) Transfer {
-			xfer := NewTransfer()
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) transfer {
+			xfer := newTransfer()
 			go func() {
 				<-start
 				totalJobs := atomic.AddInt32(&runningJobs, 1)
@@ -91,7 +91,7 @@ func TestConcurrencyLimit(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(concurrencyLimit)
+	tm := newTransferManager(concurrencyLimit)
 	progressChan := make(chan progress.Progress)
 	progressDone := make(chan struct{})
 	receivedProgress := make(map[string]int64)
@@ -105,15 +105,15 @@ func TestConcurrencyLimit(t *testing.T) {
 
 	// Start more transfers than the concurrency limit
 	ids := []string{"id1", "id2", "id3", "id4", "id5", "id6", "id7", "id8"}
-	xfers := make([]Transfer, len(ids))
-	watchers := make([]*Watcher, len(ids))
+	xfers := make([]transfer, len(ids))
+	watchers := make([]*watcher, len(ids))
 	for i, id := range ids {
-		xfers[i], watchers[i] = tm.Transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
+		xfers[i], watchers[i] = tm.transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
 	}
 
 	for i, xfer := range xfers {
-		<-xfer.Done()
-		xfer.Release(watchers[i])
+		<-xfer.done()
+		xfer.release(watchers[i])
 	}
 	close(progressChan)
 	<-progressDone
@@ -126,13 +126,13 @@ func TestConcurrencyLimit(t *testing.T) {
 }
 
 func TestInactiveJobs(t *testing.T) {
-	concurrencyLimit := 3
+	const concurrencyLimit = 3
 	var runningJobs int32
 	testDone := make(chan struct{})
 
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer {
-			xfer := NewTransfer()
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) transfer {
+			xfer := newTransfer()
 			go func() {
 				<-start
 				totalJobs := atomic.AddInt32(&runningJobs, 1)
@@ -152,7 +152,7 @@ func TestInactiveJobs(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(concurrencyLimit)
+	tm := newTransferManager(concurrencyLimit)
 	progressChan := make(chan progress.Progress)
 	progressDone := make(chan struct{})
 	receivedProgress := make(map[string]int64)
@@ -166,16 +166,16 @@ func TestInactiveJobs(t *testing.T) {
 
 	// Start more transfers than the concurrency limit
 	ids := []string{"id1", "id2", "id3", "id4", "id5", "id6", "id7", "id8"}
-	xfers := make([]Transfer, len(ids))
-	watchers := make([]*Watcher, len(ids))
+	xfers := make([]transfer, len(ids))
+	watchers := make([]*watcher, len(ids))
 	for i, id := range ids {
-		xfers[i], watchers[i] = tm.Transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
+		xfers[i], watchers[i] = tm.transfer(id, makeXferFunc(id), progress.ChanOutput(progressChan))
 	}
 
 	close(testDone)
 	for i, xfer := range xfers {
-		<-xfer.Done()
-		xfer.Release(watchers[i])
+		<-xfer.done()
+		xfer.release(watchers[i])
 	}
 	close(progressChan)
 	<-progressDone
@@ -190,9 +190,9 @@ func TestInactiveJobs(t *testing.T) {
 func TestWatchRelease(t *testing.T) {
 	ready := make(chan struct{})
 
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) Transfer {
-			xfer := NewTransfer()
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, start <-chan struct{}, _ chan<- struct{}) transfer {
+			xfer := newTransfer()
 			go func() {
 				defer func() {
 					close(progressChan)
@@ -201,7 +201,7 @@ func TestWatchRelease(t *testing.T) {
 				for i := int64(0); ; i++ {
 					select {
 					case <-time.After(10 * time.Millisecond):
-					case <-xfer.Context().Done():
+					case <-xfer.context().Done():
 						return
 					}
 					progressChan <- progress.Progress{ID: id, Action: "testing", Current: i, Total: 10}
@@ -211,10 +211,10 @@ func TestWatchRelease(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(5)
+	tm := newTransferManager(5)
 
 	type watcherInfo struct {
-		watcher               *Watcher
+		watcher               *watcher
 		progressChan          chan progress.Progress
 		progressDone          chan struct{}
 		receivedFirstProgress chan struct{}
@@ -233,11 +233,11 @@ func TestWatchRelease(t *testing.T) {
 
 	// Start a transfer
 	watchers := make([]watcherInfo, 5)
-	var xfer Transfer
+	var xfer transfer
 	watchers[0].progressChan = make(chan progress.Progress)
 	watchers[0].progressDone = make(chan struct{})
 	watchers[0].receivedFirstProgress = make(chan struct{})
-	xfer, watchers[0].watcher = tm.Transfer("id1", makeXferFunc("id1"), progress.ChanOutput(watchers[0].progressChan))
+	xfer, watchers[0].watcher = tm.transfer("id1", makeXferFunc("id1"), progress.ChanOutput(watchers[0].progressChan))
 	go progressConsumer(watchers[0])
 
 	// Give it multiple watchers
@@ -245,7 +245,7 @@ func TestWatchRelease(t *testing.T) {
 		watchers[i].progressChan = make(chan progress.Progress)
 		watchers[i].progressDone = make(chan struct{})
 		watchers[i].receivedFirstProgress = make(chan struct{})
-		watchers[i].watcher = xfer.Watch(progress.ChanOutput(watchers[i].progressChan))
+		watchers[i].watcher = xfer.watch(progress.ChanOutput(watchers[i].progressChan))
 		go progressConsumer(watchers[i])
 	}
 
@@ -260,17 +260,17 @@ func TestWatchRelease(t *testing.T) {
 
 	// Release one watcher every 5ms
 	for _, w := range watchers {
-		xfer.Release(w.watcher)
+		xfer.release(w.watcher)
 		<-time.After(5 * time.Millisecond)
 	}
 
 	// Now that all watchers have been released, Released() should
 	// return a closed channel.
-	<-xfer.Released()
+	<-xfer.released()
 
 	// Done() should return a closed channel because the xfer func returned
 	// due to cancellation.
-	<-xfer.Done()
+	<-xfer.done()
 
 	for _, w := range watchers {
 		close(w.progressChan)
@@ -279,9 +279,9 @@ func TestWatchRelease(t *testing.T) {
 }
 
 func TestWatchFinishedTransfer(t *testing.T) {
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, _ <-chan struct{}, _ chan<- struct{}) Transfer {
-			xfer := NewTransfer()
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, _ <-chan struct{}, _ chan<- struct{}) transfer {
+			xfer := newTransfer()
 			go func() {
 				// Finish immediately
 				close(progressChan)
@@ -290,30 +290,30 @@ func TestWatchFinishedTransfer(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(5)
+	tm := newTransferManager(5)
 
 	// Start a transfer
-	watchers := make([]*Watcher, 3)
-	var xfer Transfer
-	xfer, watchers[0] = tm.Transfer("id1", makeXferFunc("id1"), progress.ChanOutput(make(chan progress.Progress)))
+	watchers := make([]*watcher, 3)
+	var xfer transfer
+	xfer, watchers[0] = tm.transfer("id1", makeXferFunc("id1"), progress.ChanOutput(make(chan progress.Progress)))
 
 	// Give it a watcher immediately
-	watchers[1] = xfer.Watch(progress.ChanOutput(make(chan progress.Progress)))
+	watchers[1] = xfer.watch(progress.ChanOutput(make(chan progress.Progress)))
 
 	// Wait for the transfer to complete
-	<-xfer.Done()
+	<-xfer.done()
 
 	// Set up another watcher
-	watchers[2] = xfer.Watch(progress.ChanOutput(make(chan progress.Progress)))
+	watchers[2] = xfer.watch(progress.ChanOutput(make(chan progress.Progress)))
 
 	// Release the watchers
 	for _, w := range watchers {
-		xfer.Release(w)
+		xfer.release(w)
 	}
 
 	// Now that all watchers have been released, Released() should
 	// return a closed channel.
-	<-xfer.Released()
+	<-xfer.released()
 }
 
 func TestDuplicateTransfer(t *testing.T) {
@@ -321,10 +321,10 @@ func TestDuplicateTransfer(t *testing.T) {
 
 	var xferFuncCalls int32
 
-	makeXferFunc := func(id string) DoFunc {
-		return func(progressChan chan<- progress.Progress, _ <-chan struct{}, _ chan<- struct{}) Transfer {
+	makeXferFunc := func(id string) doFunc {
+		return func(progressChan chan<- progress.Progress, _ <-chan struct{}, _ chan<- struct{}) transfer {
 			atomic.AddInt32(&xferFuncCalls, 1)
-			xfer := NewTransfer()
+			xfer := newTransfer()
 			go func() {
 				defer func() {
 					close(progressChan)
@@ -333,7 +333,7 @@ func TestDuplicateTransfer(t *testing.T) {
 				for i := int64(0); ; i++ {
 					select {
 					case <-time.After(10 * time.Millisecond):
-					case <-xfer.Context().Done():
+					case <-xfer.context().Done():
 						return
 					}
 					progressChan <- progress.Progress{ID: id, Action: "testing", Current: i, Total: 10}
@@ -343,11 +343,11 @@ func TestDuplicateTransfer(t *testing.T) {
 		}
 	}
 
-	tm := NewTransferManager(5)
+	tm := newTransferManager(5)
 
 	type transferInfo struct {
-		xfer                  Transfer
-		watcher               *Watcher
+		xfer                  transfer
+		watcher               *watcher
 		progressChan          chan progress.Progress
 		progressDone          chan struct{}
 		receivedFirstProgress chan struct{}
@@ -371,7 +371,7 @@ func TestDuplicateTransfer(t *testing.T) {
 		t.progressChan = make(chan progress.Progress)
 		t.progressDone = make(chan struct{})
 		t.receivedFirstProgress = make(chan struct{})
-		t.xfer, t.watcher = tm.Transfer("id1", makeXferFunc("id1"), progress.ChanOutput(t.progressChan))
+		t.xfer, t.watcher = tm.transfer("id1", makeXferFunc("id1"), progress.ChanOutput(t.progressChan))
 		go progressConsumer(*t)
 	}
 
@@ -390,17 +390,17 @@ func TestDuplicateTransfer(t *testing.T) {
 
 	// Release one watcher every 5ms
 	for _, t := range transfers {
-		t.xfer.Release(t.watcher)
+		t.xfer.release(t.watcher)
 		<-time.After(5 * time.Millisecond)
 	}
 
 	for _, t := range transfers {
 		// Now that all watchers have been released, Released() should
 		// return a closed channel.
-		<-t.xfer.Released()
+		<-t.xfer.released()
 		// Done() should return a closed channel because the xfer func returned
 		// due to cancellation.
-		<-t.xfer.Done()
+		<-t.xfer.done()
 	}
 
 	for _, t := range transfers {
diff --git a/distribution/xfer/upload.go b/distribution/xfer/upload.go
index 33b45ad747..40705bad6c 100644
--- a/distribution/xfer/upload.go
+++ b/distribution/xfer/upload.go
@@ -16,19 +16,19 @@ const maxUploadAttempts = 5
 // LayerUploadManager provides task management and progress reporting for
 // uploads.
 type LayerUploadManager struct {
-	tm           TransferManager
+	tm           *transferManager
 	waitDuration time.Duration
 }
 
 // SetConcurrency sets the max concurrent uploads for each push
 func (lum *LayerUploadManager) SetConcurrency(concurrency int) {
-	lum.tm.SetConcurrency(concurrency)
+	lum.tm.setConcurrency(concurrency)
 }
 
 // NewLayerUploadManager returns a new LayerUploadManager.
 func NewLayerUploadManager(concurrencyLimit int, options ...func(*LayerUploadManager)) *LayerUploadManager {
 	manager := LayerUploadManager{
-		tm:           NewTransferManager(concurrencyLimit),
+		tm:           newTransferManager(concurrencyLimit),
 		waitDuration: time.Second,
 	}
 	for _, option := range options {
@@ -38,7 +38,7 @@ func NewLayerUploadManager(concurrencyLimit int, options ...func(*LayerUploadMan
 }
 
 type uploadTransfer struct {
-	Transfer
+	transfer
 
 	remoteDescriptor distribution.Descriptor
 	err              error
@@ -79,8 +79,8 @@ func (lum *LayerUploadManager) Upload(ctx context.Context, layers []UploadDescri
 		}
 
 		xferFunc := lum.makeUploadFunc(descriptor)
-		upload, watcher := lum.tm.Transfer(descriptor.Key(), xferFunc, progressOutput)
-		defer upload.Release(watcher)
+		upload, watcher := lum.tm.transfer(descriptor.Key(), xferFunc, progressOutput)
+		defer upload.release(watcher)
 		uploads = append(uploads, upload.(*uploadTransfer))
 		dedupDescriptors[key] = upload.(*uploadTransfer)
 	}
@@ -89,7 +89,7 @@ func (lum *LayerUploadManager) Upload(ctx context.Context, layers []UploadDescri
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
-		case <-upload.Transfer.Done():
+		case <-upload.transfer.done():
 			if upload.err != nil {
 				return upload.err
 			}
@@ -102,10 +102,10 @@ func (lum *LayerUploadManager) Upload(ctx context.Context, layers []UploadDescri
 	return nil
 }
 
-func (lum *LayerUploadManager) makeUploadFunc(descriptor UploadDescriptor) DoFunc {
-	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) Transfer {
+func (lum *LayerUploadManager) makeUploadFunc(descriptor UploadDescriptor) doFunc {
+	return func(progressChan chan<- progress.Progress, start <-chan struct{}, inactive chan<- struct{}) transfer {
 		u := &uploadTransfer{
-			Transfer: NewTransfer(),
+			transfer: newTransfer(),
 		}
 
 		go func() {
@@ -124,7 +124,7 @@ func (lum *LayerUploadManager) makeUploadFunc(descriptor UploadDescriptor) DoFun
 
 			retries := 0
 			for {
-				remoteDescriptor, err := descriptor.Upload(u.Transfer.Context(), progressOutput)
+				remoteDescriptor, err := descriptor.Upload(u.transfer.context(), progressOutput)
 				if err == nil {
 					u.remoteDescriptor = remoteDescriptor
 					break
@@ -133,7 +133,7 @@ func (lum *LayerUploadManager) makeUploadFunc(descriptor UploadDescriptor) DoFun
 				// If an error was returned because the context
 				// was cancelled, we shouldn't retry.
 				select {
-				case <-u.Transfer.Context().Done():
+				case <-u.transfer.context().Done():
 					u.err = err
 					return
 				default:
@@ -160,7 +160,7 @@ func (lum *LayerUploadManager) makeUploadFunc(descriptor UploadDescriptor) DoFun
 							ticker.Stop()
 							break selectLoop
 						}
-					case <-u.Transfer.Context().Done():
+					case <-u.transfer.context().Done():
 						ticker.Stop()
 						u.err = errors.New("upload cancelled during retry delay")
 						return
diff --git a/distribution/xfer/upload_test.go b/distribution/xfer/upload_test.go
index 4507feac7b..9150a63d7a 100644
--- a/distribution/xfer/upload_test.go
+++ b/distribution/xfer/upload_test.go
@@ -69,12 +69,12 @@ func (u *mockUploadDescriptor) Upload(ctx context.Context, progressOutput progre
 
 func uploadDescriptors(currentUploads *int32) []UploadDescriptor {
 	return []UploadDescriptor{
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:cbbf2f9a99b47fc460d422812b6a5adff7dfee951d8fa2e4a98caa0382cfbdbf"), 0},
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:1515325234325236634634608943609283523908626098235490238423902343"), 0},
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:6929356290463485374960346430698374523437683470934634534953453453"), 0},
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:cbbf2f9a99b47fc460d422812b6a5adff7dfee951d8fa2e4a98caa0382cfbdbf"), 0},
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:8159352387436803946235346346368745389534789534897538734598734987"), 1},
-		&mockUploadDescriptor{currentUploads, layer.DiffID("sha256:4637863963478346897346987346987346789346789364879364897364987346"), 0},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:cbbf2f9a99b47fc460d422812b6a5adff7dfee951d8fa2e4a98caa0382cfbdbf"},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:1515325234325236634634608943609283523908626098235490238423902343"},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:6929356290463485374960346430698374523437683470934634534953453453"},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:cbbf2f9a99b47fc460d422812b6a5adff7dfee951d8fa2e4a98caa0382cfbdbf"},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:8159352387436803946235346346368745389534789534897538734598734987", simulateRetries: 1},
+		&mockUploadDescriptor{currentUploads: currentUploads, diffID: "sha256:4637863963478346897346987346987346789346789364879364897364987346"},
 	}
 }