1// SPDX-License-Identifier: GPL-2.0
2#include <linux/types.h>
3#include <linux/errno.h>
4#include <linux/tty.h>
5#include <linux/module.h>
6
7/*
8 * n_null.c - Null line discipline used in the failure path
9 *
10 * Copyright (C) Intel 2017
11 */
12
13static int n_null_open(struct tty_struct *tty)
14{
15 return 0;
16}
17
18static void n_null_close(struct tty_struct *tty)
19{
20}
21
22static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
23 unsigned char __user * buf, size_t nr)
24{
25 return -EOPNOTSUPP;
26}
27
28static ssize_t n_null_write(struct tty_struct *tty, struct file *file,
29 const unsigned char *buf, size_t nr)
30{
31 return -EOPNOTSUPP;
32}
33
34static void n_null_receivebuf(struct tty_struct *tty,
35 const unsigned char *cp, char *fp,
36 int cnt)
37{
38}
39
40static struct tty_ldisc_ops null_ldisc = {
41 .owner = THIS_MODULE,
42 .magic = TTY_LDISC_MAGIC,
43 .name = "n_null",
44 .open = n_null_open,
45 .close = n_null_close,
46 .read = n_null_read,
47 .write = n_null_write,
48 .receive_buf = n_null_receivebuf
49};
50
51static int __init n_null_init(void)
52{
53 BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc));
54 return 0;
55}
56
57static void __exit n_null_exit(void)
58{
59 tty_unregister_ldisc(N_NULL);
60}
61
62module_init(n_null_init);
63module_exit(n_null_exit);
64
65MODULE_LICENSE("GPL");
66MODULE_AUTHOR("Alan Cox");
67MODULE_ALIAS_LDISC(N_NULL);
68MODULE_DESCRIPTION("Null ldisc driver");
69