it works

vfs/vfserror/vfserror.go

@@ -0,0 +1,14 @@
+package vfserror
+
+import "errors"
+
+var (
+	// ErrUnreachable is returned when a code path is unreachable.
+	ErrUnreachable = errors.New("unreachable")
+
+	// ErrNotFound is returned when a key is not found.
+	ErrNotFound = errors.New("vfs: key not found")
+
+	// ErrDiskFull is returned when the disk is full.
+	ErrDiskFull = errors.New("vfs: disk full")
+)