[#1367] fstree: Add size to file counter

FSTree file counter used by writecache. As writecache has now only one
storage, so it is required to use real object size to get writecache
size more accurate than `count * max_object_size`.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/blobstor/fstree/fstree.go

@@ -435,32 +435,38 @@ func (t *FSTree) initFileCounter() error {
 		return nil
 	}
 
-	counter, err := t.countFiles()
+	count, size, err := t.countFiles()
 	if err != nil {
 		return err
 	}
-	t.fileCounter.Set(counter)
+	t.fileCounter.Set(count, size)
 	return nil
 }
 
-func (t *FSTree) countFiles() (uint64, error) {
-	var counter uint64
+func (t *FSTree) countFiles() (uint64, uint64, error) {
+	var count, size uint64
 	// it is simpler to just consider every file
 	// that is not directory as an object
 	err := filepath.WalkDir(t.RootPath,
 		func(_ string, d fs.DirEntry, _ error) error {
-			if !d.IsDir() {
-				counter++
+			if d.IsDir() {
+				return nil
 			}
+			count++
+			info, err := d.Info()
+			if err != nil {
+				return err
+			}
+			size += uint64(info.Size())
 
 			return nil
 		},
 	)
 	if err != nil {
-		return 0, fmt.Errorf("could not walk through %s directory: %w", t.RootPath, err)
+		return 0, 0, fmt.Errorf("could not walk through %s directory: %w", t.RootPath, err)
 	}
 
-	return counter, nil
+	return count, size, nil
 }
 
 func (t *FSTree) ObjectsCount(ctx context.Context) (uint64, error) {