drivers/tty/ttynull.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2019 Axis Communications AB
   4  *
   5  * Based on ttyprintk.c:
   6  *  Copyright (C) 2010 Samo Pogacnik
   7  */
   8
   9 #include <linux/console.h>
  10 #include <linux/module.h>
  11 #include <linux/tty.h>
  12
  13 static const struct tty_port_operations ttynull_port_ops;
  14 static struct tty_driver *ttynull_driver;
  15 static struct tty_port ttynull_port;
  16
  17 static int ttynull_open(struct tty_struct *tty, struct file *filp)
  18 {
  19         return tty_port_open(&ttynull_port, tty, filp);
  20 }
  21
  22 static void ttynull_close(struct tty_struct *tty, struct file *filp)
  23 {
  24         tty_port_close(&ttynull_port, tty, filp);
  25 }
  26
  27 static void ttynull_hangup(struct tty_struct *tty)
  28 {
  29         tty_port_hangup(&ttynull_port);
  30 }
  31
  32 static int ttynull_write(struct tty_struct *tty, const unsigned char *buf,
  33                          int count)
  34 {
  35         return count;
  36 }
  37
  38 static int ttynull_write_room(struct tty_struct *tty)
  39 {
  40         return 65536;
  41 }
  42
  43 static const struct tty_operations ttynull_ops = {
  44         .open = ttynull_open,
  45         .close = ttynull_close,
  46         .hangup = ttynull_hangup,
  47         .write = ttynull_write,
  48         .write_room = ttynull_write_room,
  49 };
  50
  51 static struct tty_driver *ttynull_device(struct console *c, int *index)
  52 {
  53         *index = 0;
  54         return ttynull_driver;
  55 }
  56
  57 static struct console ttynull_console = {
  58         .name = "ttynull",
  59         .device = ttynull_device,
  60 };
  61
  62 static int __init ttynull_init(void)
  63 {
  64         struct tty_driver *driver;
  65         int ret;
  66
  67         driver = tty_alloc_driver(1,
  68                 TTY_DRIVER_RESET_TERMIOS |
  69                 TTY_DRIVER_REAL_RAW |
  70                 TTY_DRIVER_UNNUMBERED_NODE);
  71         if (IS_ERR(driver))
  72                 return PTR_ERR(driver);
  73
  74         tty_port_init(&ttynull_port);
  75         ttynull_port.ops = &ttynull_port_ops;
  76
  77         driver->driver_name = "ttynull";
  78         driver->name = "ttynull";
  79         driver->type = TTY_DRIVER_TYPE_CONSOLE;
  80         driver->init_termios = tty_std_termios;
  81         driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
  82         tty_set_operations(driver, &ttynull_ops);
  83         tty_port_link_device(&ttynull_port, driver, 0);
  84
  85         ret = tty_register_driver(driver);
  86         if (ret < 0) {
  87                 put_tty_driver(driver);
  88                 tty_port_destroy(&ttynull_port);
  89                 return ret;
  90         }
  91
  92         ttynull_driver = driver;
  93         register_console(&ttynull_console);
  94
  95         return 0;
  96 }
  97
  98 static void __exit ttynull_exit(void)
  99 {
 100         unregister_console(&ttynull_console);
 101         tty_unregister_driver(ttynull_driver);
 102         put_tty_driver(ttynull_driver);
 103         tty_port_destroy(&ttynull_port);
 104 }
 105
 106 module_init(ttynull_init);
 107 module_exit(ttynull_exit);
 108
 109 MODULE_LICENSE("GPL v2");