drivers: add new method SupportsShifting() to LayerIDMapUpdater

Signed-off-by: Giuseppe Scrivano <[email protected]>

drivers/aufs/aufs.go

@@ -728,3 +728,8 @@ func useDirperm() bool {
 func (a *Driver) UpdateLayerIDMap(id string, toContainer, toHost *idtools.IDMappings, mountLabel string) error {
 	return fmt.Errorf("aufs doesn't support changing ID mappings")
 }
+
+// SupportsShifting tells whether the driver support shifting of the UIDs/GIDs in an userNS
+func (a *Driver) SupportsShifting() bool {
+	return false
+}

drivers/chown.go

@@ -124,3 +124,8 @@ func (n *naiveLayerIDMapUpdater) UpdateLayerIDMap(id string, toContainer, toHost
 
 	return ChownPathByMaps(layerFs, toContainer, toHost)
 }
+
+// SupportsShifting tells whether the driver support shifting of the UIDs/GIDs in an userNS
+func (n *naiveLayerIDMapUpdater) SupportsShifting() bool {
+	return false
+}

drivers/driver.go

@@ -118,6 +118,10 @@ type LayerIDMapUpdater interface {
 	// relative to a parent layer, but before this method is called, may be discarded
 	// by Diff().
 	UpdateLayerIDMap(id string, toContainer, toHost *idtools.IDMappings, mountLabel string) error
+
+	// SupportsShifting tells whether the driver support shifting of the UIDs/GIDs in a
+	// image and it is not required to Chown the files when running in an user namespace.
+	SupportsShifting() bool
 }
 
 // Driver is the interface for layered/snapshot file system drivers.

drivers/windows/windows.go

@@ -954,6 +954,11 @@ func (d *Driver) UpdateLayerIDMap(id string, toContainer, toHost *idtools.IDMapp
 	return fmt.Errorf("windows doesn't support changing ID mappings")
 }
 
+// SupportsShifting tells whether the driver support shifting of the UIDs/GIDs in an userNS
+func (d *Driver) SupportsShifting() bool {
+	return false
+}
+
 type storageOptions struct {
 	size uint64
 }