drivers/tty/n_null.c

   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 __user * buf, size_t nr)
  24 {
  25         return -EOPNOTSUPP;
  26 }
  27
  28 static 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
  34 static void n_null_receivebuf(struct tty_struct *tty,
  35                                  const unsigned char *cp, char *fp,
  36                                  int cnt)
  37 {
  38 }
  39
  40 static 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
  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");