// 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 *buf, size_t nr,			   void **cookie, unsigned long offset){	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,	.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");