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, char *fp, 37 int cnt) 38 { 39 } 40 41 static struct tty_ldisc_ops null_ldisc = { 42 .owner = THIS_MODULE, 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 51 static int __init n_null_init(void) 52 { 53 BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc)); 54 return 0; 55 } 56 57 static void __exit n_null_exit(void) 58 { 59 tty_unregister_ldisc(N_NULL); 60 } 61 62 module_init(n_null_init); 63 module_exit(n_null_exit); 64 65 MODULE_LICENSE("GPL"); 66 MODULE_AUTHOR("Alan Cox"); 67 MODULE_ALIAS_LDISC(N_NULL); 68 MODULE_DESCRIPTION("Null ldisc driver"); 69