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 *buf, size_t nr, 24 void **cookie, unsigned long offset) 25{ 26 return -EOPNOTSUPP; 27} 28 29static 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 35static void n_null_receivebuf(struct tty_struct *tty, 36 const unsigned char *cp, char *fp, 37 int cnt) 38{ 39} 40 41static struct tty_ldisc_ops null_ldisc = { 42 .owner = THIS_MODULE, 43 .magic = TTY_LDISC_MAGIC, 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 52static int __init n_null_init(void) 53{ 54 BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc)); 55 return 0; 56} 57 58static void __exit n_null_exit(void) 59{ 60 tty_unregister_ldisc(N_NULL); 61} 62 63module_init(n_null_init); 64module_exit(n_null_exit); 65 66MODULE_LICENSE("GPL"); 67MODULE_AUTHOR("Alan Cox"); 68MODULE_ALIAS_LDISC(N_NULL); 69MODULE_DESCRIPTION("Null ldisc driver"); 70