v4.19.13 snapshot.
diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
new file mode 100644
index 0000000..3594208
--- /dev/null
+++ b/include/linux/mnt_namespace.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NAMESPACE_H_
+#define _NAMESPACE_H_
+#ifdef __KERNEL__
+
+struct mnt_namespace;
+struct fs_struct;
+struct user_namespace;
+
+extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
+ struct user_namespace *, struct fs_struct *);
+extern void put_mnt_ns(struct mnt_namespace *ns);
+
+extern const struct file_operations proc_mounts_operations;
+extern const struct file_operations proc_mountinfo_operations;
+extern const struct file_operations proc_mountstats_operations;
+
+#endif
+#endif