Move all the "lower"-related functions to single place.

Only moves unchanged code, should not change behavior.

Also document the difference between getLowerDirs and
getLowerDiffPaths.

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

Author: mtrmac

storage/drivers/overlay/overlay.go

@@ -1238,6 +1238,47 @@ func (d *Driver) parseStorageOpt(storageOpt map[string]string, driver *Driver) e
 	return nil
 }
 
+func (d *Driver) dir(id string) string {
+	p, _, _ := d.dir2(id, false)
+	return p
+}
+
+func (d *Driver) getAllImageStores() []string {
+	additionalImageStores := d.AdditionalImageStores()
+	if d.imageStore != "" {
+		additionalImageStores = append([]string{d.imageStore}, additionalImageStores...)
+	}
+	return additionalImageStores
+}
+
+// homeDirForImageStore returns the home directory to use when an image store is configured
+func (d *Driver) homeDirForImageStore() string {
+	if d.imageStore != "" {
+		return path.Join(d.imageStore, d.name)
+	}
+	// If there is not an image store configured, use the same
+	// store
+	return d.home
+}
+
+func (d *Driver) dir2(id string, useImageStore bool) (string, string, bool) {
+	homedir := d.home
+	if useImageStore {
+		homedir = d.homeDirForImageStore()
+	}
+	newpath := path.Join(homedir, id)
+	if err := fileutils.Exists(newpath); err != nil {
+		for _, p := range d.getAllImageStores() {
+			l := path.Join(p, d.name, id)
+			err = fileutils.Exists(l)
+			if err == nil {
+				return l, homedir, true
+			}
+		}
+	}
+	return newpath, homedir, false
+}
+
 // getLowerForParent returns the contents of lowerFile for a child layer of parent.
 //
 // This should only be used to construct a lowerFile for compatibility;
@@ -1303,47 +1344,8 @@ func (d *Driver) getLowerLayerIDs(id string) ([]string, error) {
 	}
 }
 
-func (d *Driver) dir(id string) string {
-	p, _, _ := d.dir2(id, false)
-	return p
-}
-
-func (d *Driver) getAllImageStores() []string {
-	additionalImageStores := d.AdditionalImageStores()
-	if d.imageStore != "" {
-		additionalImageStores = append([]string{d.imageStore}, additionalImageStores...)
-	}
-	return additionalImageStores
-}
-
-// homeDirForImageStore returns the home directory to use when an image store is configured
-func (d *Driver) homeDirForImageStore() string {
-	if d.imageStore != "" {
-		return path.Join(d.imageStore, d.name)
-	}
-	// If there is not an image store configured, use the same
-	// store
-	return d.home
-}
-
-func (d *Driver) dir2(id string, useImageStore bool) (string, string, bool) {
-	homedir := d.home
-	if useImageStore {
-		homedir = d.homeDirForImageStore()
-	}
-	newpath := path.Join(homedir, id)
-	if err := fileutils.Exists(newpath); err != nil {
-		for _, p := range d.getAllImageStores() {
-			l := path.Join(p, d.name, id)
-			err = fileutils.Exists(l)
-			if err == nil {
-				return l, homedir, true
-			}
-		}
-	}
-	return newpath, homedir, false
-}
-
+// getLowerDirs returns a list of lower directories for a layer id;
+// the directories may be symbolic links (do not call redirectDiffIfAdditionalLayer).
 func (d *Driver) getLowerDirs(id string) ([]string, error) {
 	lowerLayerIDs, err := d.getLowerLayerIDs(id)
 	if err != nil {
@@ -1357,6 +1359,22 @@ func (d *Driver) getLowerDirs(id string) ([]string, error) {
 	return lowersArray, nil
 }
 
+// getLowerDiffPaths returns a list of lower diff paths for a layer id;
+// the paths have redirectDiffIfAdditionalLayer applied.
+func (d *Driver) getLowerDiffPaths(id string) ([]string, error) {
+	layers, err := d.getLowerDirs(id)
+	if err != nil {
+		return nil, err
+	}
+	for i, l := range layers {
+		layers[i], err = redirectDiffIfAdditionalLayer(l, false)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return layers, nil
+}
+
 func (d *Driver) optsAppendMappings(opts string, uidMaps, gidMaps []idtools.IDMap) string {
 	if uidMaps != nil {
 		var uids, gids bytes.Buffer
@@ -2419,20 +2437,6 @@ func (d *Driver) getDiffPath(id string) (string, error) {
 	return redirectDiffIfAdditionalLayer(path.Join(dir, "diff"), false)
 }
 
-func (d *Driver) getLowerDiffPaths(id string) ([]string, error) {
-	layers, err := d.getLowerDirs(id)
-	if err != nil {
-		return nil, err
-	}
-	for i, l := range layers {
-		layers[i], err = redirectDiffIfAdditionalLayer(l, false)
-		if err != nil {
-			return nil, err
-		}
-	}
-	return layers, nil
-}
-
 // DiffSize calculates the changes between the specified id
 // and its parent and returns the size in bytes of the changes
 // relative to its base filesystem directory.