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 13 static int n_null_open(struct tty_struct *tty) 14 { 15 return 0; 16 } 17 18 static void n_null_close(struct tty_struct *tty) 19 { 20 } 21 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 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 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 52 static int __init n_null_init(void) 53 { 54 BUG_ON(tty_register_ldisc(&null_ldisc)); 55 return 0; 56 } 57 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