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
n_null_open(struct tty_struct * tty)13 static int n_null_open(struct tty_struct *tty)
14 {
15 return 0;
16 }
17
n_null_close(struct tty_struct * tty)18 static void n_null_close(struct tty_struct *tty)
19 {
20 }
21
n_null_read(struct tty_struct * tty,struct file * file,unsigned char * buf,size_t nr,void ** cookie,unsigned long offset)22 static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
23 unsigned char *buf, size_t nr,
24 void **cookie, unsigned long offset)
25 {
26 return -EOPNOTSUPP;
27 }
28
n_null_write(struct tty_struct * tty,struct file * file,const unsigned char * buf,size_t nr)29 static ssize_t n_null_write(struct tty_struct *tty, struct file *file,
30 const unsigned char *buf, size_t nr)
31 {
32 return -EOPNOTSUPP;
33 }
34
n_null_receivebuf(struct tty_struct * tty,const unsigned char * cp,const char * fp,int cnt)35 static void n_null_receivebuf(struct tty_struct *tty,
36 const unsigned char *cp, const char *fp,
37 int cnt)
38 {
39 }
40
41 static struct tty_ldisc_ops null_ldisc = {
42 .owner = THIS_MODULE,
43 .num = N_NULL,
44 .name = "n_null",
45 .open = n_null_open,
46 .close = n_null_close,
47 .read = n_null_read,
48 .write = n_null_write,
49 .receive_buf = n_null_receivebuf
50 };
51
n_null_init(void)52 static int __init n_null_init(void)
53 {
54 BUG_ON(tty_register_ldisc(&null_ldisc));
55 return 0;
56 }
57
n_null_exit(void)58 static void __exit n_null_exit(void)
59 {
60 tty_unregister_ldisc(&null_ldisc);
61 }
62
63 module_init(n_null_init);
64 module_exit(n_null_exit);
65
66 MODULE_LICENSE("GPL");
67 MODULE_AUTHOR("Alan Cox");
68 MODULE_ALIAS_LDISC(N_NULL);
69 MODULE_DESCRIPTION("Null ldisc driver");
70