v4.19.13 snapshot.
diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
new file mode 100644
index 0000000..5fbc400
--- /dev/null
+++ b/include/linux/ns_common.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_NS_COMMON_H
+#define _LINUX_NS_COMMON_H
+
+struct proc_ns_operations;
+
+struct ns_common {
+	atomic_long_t stashed;
+	const struct proc_ns_operations *ops;
+	unsigned int inum;
+};
+
+#endif