v4.19.13 snapshot.
diff --git a/drivers/tty/n_null.c b/drivers/tty/n_null.c
new file mode 100644
index 0000000..96feaba
--- /dev/null
+++ b/drivers/tty/n_null.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/tty.h>
+#include <linux/module.h>
+
+/*
+ * n_null.c - Null line discipline used in the failure path
+ *
+ * Copyright (C) Intel 2017
+ */
+
+static int n_null_open(struct tty_struct *tty)
+{
+ return 0;
+}
+
+static void n_null_close(struct tty_struct *tty)
+{
+}
+
+static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
+ unsigned char __user * buf, size_t nr)
+{
+ return -EOPNOTSUPP;
+}
+
+static ssize_t n_null_write(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr)
+{
+ return -EOPNOTSUPP;
+}
+
+static void n_null_receivebuf(struct tty_struct *tty,
+ const unsigned char *cp, char *fp,
+ int cnt)
+{
+}
+
+static struct tty_ldisc_ops null_ldisc = {
+ .owner = THIS_MODULE,
+ .magic = TTY_LDISC_MAGIC,
+ .name = "n_null",
+ .open = n_null_open,
+ .close = n_null_close,
+ .read = n_null_read,
+ .write = n_null_write,
+ .receive_buf = n_null_receivebuf
+};
+
+static int __init n_null_init(void)
+{
+ BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc));
+ return 0;
+}
+
+static void __exit n_null_exit(void)
+{
+ tty_unregister_ldisc(N_NULL);
+}
+
+module_init(n_null_init);
+module_exit(n_null_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Alan Cox");
+MODULE_ALIAS_LDISC(N_NULL);
+MODULE_DESCRIPTION("Null ldisc driver");