drivers/tty/n_null.c

   1 #include <linux/types.h>
   2 #include <linux/errno.h>
   3 #include <linux/tty.h>
   4 #include <linux/module.h>
   5
   6 /*
   7  *  n_null.c - Null line discipline used in the failure path
   8  *
   9  *  Copyright (C) Intel 2017
  10  *
  11  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  12  *
  13  *  This program is free software; you can redistribute it and/or modify
  14  *  it under the terms of the GNU General Public License version 2
  15  *  as published by the Free Software Foundation.
  16  *
  17  *  This program is distributed in the hope that it will be useful,
  18  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  *  GNU General Public License for more details.
  21  *
  22  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  23  */
  24
  25 static int n_null_open(struct tty_struct *tty)
  26 {
  27         return 0;
  28 }
  29
  30 static void n_null_close(struct tty_struct *tty)
  31 {
  32 }
  33
  34 static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
  35                            unsigned char __user * buf, size_t nr)
  36 {
  37         return -EOPNOTSUPP;
  38 }
  39
  40 static ssize_t n_null_write(struct tty_struct *tty, struct file *file,
  41                             const unsigned char *buf, size_t nr)
  42 {
  43         return -EOPNOTSUPP;
  44 }
  45
  46 static void n_null_receivebuf(struct tty_struct *tty,
  47                                  const unsigned char *cp, char *fp,
  48                                  int cnt)
  49 {
  50 }
  51
  52 static struct tty_ldisc_ops null_ldisc = {
  53         .owner          =       THIS_MODULE,
  54         .magic          =       TTY_LDISC_MAGIC,
  55         .name           =       "n_null",
  56         .open           =       n_null_open,
  57         .close          =       n_null_close,
  58         .read           =       n_null_read,
  59         .write          =       n_null_write,
  60         .receive_buf    =       n_null_receivebuf
  61 };
  62
  63 static int __init n_null_init(void)
  64 {
  65         BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc));
  66         return 0;
  67 }
  68
  69 static void __exit n_null_exit(void)
  70 {
  71         tty_unregister_ldisc(N_NULL);
  72 }
  73
  74 module_init(n_null_init);
  75 module_exit(n_null_exit);
  76
  77 MODULE_LICENSE("GPL");
  78 MODULE_AUTHOR("Alan Cox");
  79 MODULE_ALIAS_LDISC(N_NULL);
  80 MODULE_DESCRIPTION("Null ldisc driver");