daemon/graphdriver: remove Capabilities, CapabilityDriver

Capabilities were implemented in aa96c3176b,
as part of work on an external graphdriver-plugin. Given that none of
the builtin graphdrivers use this option, and support for graphdriver-
plugins has been removed in 555dac5e14,
we can remove this functionality.

This patch:

- removes the CapabilityDriver interface, which has no implementations
- removes the Capabilities type
- layer: remove layerStore.useTarSplit. This field was previously set
  through the driver's Capabilities, but always enabled for the builtin
  graphdrivers,

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/driver.go

@@ -94,23 +94,6 @@ type Driver interface {
 	DiffDriver
 }
 
-// Capabilities defines a list of capabilities a driver may implement.
-// These capabilities are not required; however, they do determine how a
-// graphdriver can be used.
-type Capabilities struct {
-	// Flags that this driver is capable of reproducing exactly equivalent
-	// diffs for read-only layers. If set, clients can rely on the driver
-	// for consistent tar streams, and avoid extra processing to account
-	// for potential differences (eg: the layer store's use of tar-split).
-	ReproducesExactDiffs bool
-}
-
-// CapabilityDriver is the interface for layered file system drivers that
-// can report on their Capabilities.
-type CapabilityDriver interface {
-	Capabilities() Capabilities
-}
-
 // DiffGetterDriver is the interface for layered file system drivers that
 // provide a specialized function for getting file contents for tar-split.
 type DiffGetterDriver interface {

layer/layer_store.go

@@ -28,9 +28,8 @@ import (
 const maxLayerDepth = 125
 
 type layerStore struct {
-	store       *fileMetadataStore
-	driver      graphdriver.Driver
-	useTarSplit bool
+	store  *fileMetadataStore
+	driver graphdriver.Driver
 
 	layerMap map[ChainID]*roLayer
 	layerL   sync.Mutex
@@ -77,23 +76,17 @@ func NewStoreFromOptions(options StoreOptions) (Store, error) {
 // metadata store and graph driver. The metadata store will be used to restore
 // the Store.
 func newStoreFromGraphDriver(root string, driver graphdriver.Driver) (Store, error) {
-	caps := graphdriver.Capabilities{}
-	if capDriver, ok := driver.(graphdriver.CapabilityDriver); ok {
-		caps = capDriver.Capabilities()
-	}
-
 	ms, err := newFSMetadataStore(root)
 	if err != nil {
 		return nil, err
 	}
 
 	ls := &layerStore{
-		store:       ms,
-		driver:      driver,
-		layerMap:    map[ChainID]*roLayer{},
-		mounts:      map[string]*mountedLayer{},
-		locker:      locker.New(),
-		useTarSplit: !caps.ReproducesExactDiffs,
+		store:    ms,
+		driver:   driver,
+		layerMap: map[ChainID]*roLayer{},
+		mounts:   map[string]*mountedLayer{},
+		locker:   locker.New(),
 	}
 
 	ids, mounts, err := ms.List()
@@ -225,24 +218,21 @@ func (ls *layerStore) loadMount(mount string) error {
 }
 
 func (ls *layerStore) applyTar(tx *fileMetadataTransaction, ts io.Reader, parent string, layer *roLayer) error {
+	tsw, err := tx.TarSplitWriter(true)
+	if err != nil {
+		return err
+	}
+	metaPacker := storage.NewJSONPacker(tsw)
+	defer tsw.Close()
+
 	digester := digest.Canonical.Digester()
 	tr := io.TeeReader(ts, digester.Hash())
 
-	rdr := tr
-	if ls.useTarSplit {
-		tsw, err := tx.TarSplitWriter(true)
-		if err != nil {
-			return err
-		}
-		metaPacker := storage.NewJSONPacker(tsw)
-		defer tsw.Close()
-
-		// we're passing nil here for the file putter, because the ApplyDiff will
-		// handle the extraction of the archive
-		rdr, err = asm.NewInputTarStream(tr, metaPacker, nil)
-		if err != nil {
-			return err
-		}
+	// we're passing nil here for the file putter, because the ApplyDiff will
+	// handle the extraction of the archive
+	rdr, err := asm.NewInputTarStream(tr, metaPacker, nil)
+	if err != nil {
+		return err
 	}
 
 	applySize, err := ls.driver.ApplyDiff(layer.cacheID, parent, rdr)
@@ -690,15 +680,6 @@ func (ls *layerStore) initMount(graphID, parent, mountLabel string, initFunc Mou
 }
 
 func (ls *layerStore) getTarStream(rl *roLayer) (io.ReadCloser, error) {
-	if !ls.useTarSplit {
-		var parentCacheID string
-		if rl.parent != nil {
-			parentCacheID = rl.parent.cacheID
-		}
-
-		return ls.driver.Diff(rl.cacheID, parentCacheID)
-	}
-
 	r, err := ls.store.TarSplitReader(rl.chainID)
 	if err != nil {
 		return nil, err