Remove locker.Locker fromd drivers/overlay

In all call paths, the layerStore owning the driver
is expected to be locked, so, so this seems redundant.

See also containers#1140 (comment) .

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

drivers/overlay/overlay.go

@@ -26,7 +26,6 @@ import (
 	"github.com/containers/storage/pkg/directory"
 	"github.com/containers/storage/pkg/fsutils"
 	"github.com/containers/storage/pkg/idtools"
-	"github.com/containers/storage/pkg/locker"
 	"github.com/containers/storage/pkg/mount"
 	"github.com/containers/storage/pkg/parsers"
 	"github.com/containers/storage/pkg/system"
@@ -119,7 +118,6 @@ type Driver struct {
 	supportsDType    bool
 	supportsVolatile *bool
 	usingMetacopy    bool
-	locker           *locker.Locker
 
 	supportsIDMappedMounts *bool
 }
@@ -422,7 +420,6 @@ func Init(home string, options graphdriver.Options) (graphdriver.Driver, error)
 		supportsDType:    supportsDType,
 		usingMetacopy:    usingMetacopy,
 		supportsVolatile: supportsVolatile,
-		locker:           locker.New(),
 		options:          *opts,
 	}
 
@@ -1175,9 +1172,6 @@ func (d *Driver) optsAppendMappings(opts string, uidMaps, gidMaps []idtools.IDMa
 
 // Remove cleans the directories that are created for this id.
 func (d *Driver) Remove(id string) error {
-	d.locker.Lock(id)
-	defer d.locker.Unlock(id)
-
 	dir := d.dir(id)
 	lid, err := ioutil.ReadFile(path.Join(dir, "link"))
 	if err == nil {
@@ -1311,8 +1305,6 @@ func (d *Driver) Get(id string, options graphdriver.MountOpts) (_ string, retErr
 }
 
 func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountOpts) (_ string, retErr error) {
-	d.locker.Lock(id)
-	defer d.locker.Unlock(id)
 	dir, inAdditionalStore := d.dir2(id)
 	if _, err := os.Stat(dir); err != nil {
 		return "", err
@@ -1637,8 +1629,6 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 
 // Put unmounts the mount path created for the give id.
 func (d *Driver) Put(id string) error {
-	d.locker.Lock(id)
-	defer d.locker.Unlock(id)
 	dir := d.dir(id)
 	if _, err := os.Stat(dir); err != nil {
 		return err