Check for ErrNotExist in CopyOnWriteFs.Stat

Fixes #144

copyOnWriteFs.go

@@ -80,7 +80,7 @@ func (u *CopyOnWriteFs) Stat(name string) (os.FileInfo, error) {
 		if e, ok := err.(*os.PathError); ok {
 			err = e.Err
 		}
-		if err == syscall.ENOENT || err == syscall.ENOTDIR {
+		if err == os.ErrNotExist || err == syscall.ENOENT || err == syscall.ENOTDIR {
 			return u.base.Stat(name)
 		}
 		return nil, origErr

copyOnWriteFs_test.go

@@ -21,3 +21,19 @@ func TestCopyOnWrite(t *testing.T) {
 	}
 
 }
+
+func TestCopyOnWriteFileInMemMapBase(t *testing.T) {
+	base := &MemMapFs{}
+	layer := &MemMapFs{}
+
+	if err := WriteFile(base, "base.txt", []byte("base"), 0755); err != nil {
+		t.Fatalf("Failed to write file: %s", err)
+	}
+
+	ufs := NewCopyOnWriteFs(base, layer)
+
+	_, err := ufs.Stat("base.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+}