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 *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");