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If no console driver is enabled (or if a non-present driver is selected with something like console=null in an attempt to disable the console), opening /dev/console errors out, and init scripts and other userspace code that relies on the existence of a console will fail. Symlinking /dev/null to /dev/console does not solve the problem since /dev/null does not behave like a real TTY. To just provide a dummy console to userspace when no console driver is available or desired, add a ttynull driver which simply discards all writes. It can be chosen on the command line in the standard way, i.e. with console=ttynull. Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
110 lines
2.3 KiB
C
110 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2019 Axis Communications AB
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*
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* Based on ttyprintk.c:
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* Copyright (C) 2010 Samo Pogacnik
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*/
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#include <linux/console.h>
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#include <linux/module.h>
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#include <linux/tty.h>
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static const struct tty_port_operations ttynull_port_ops;
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static struct tty_driver *ttynull_driver;
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static struct tty_port ttynull_port;
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static int ttynull_open(struct tty_struct *tty, struct file *filp)
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{
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return tty_port_open(&ttynull_port, tty, filp);
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}
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static void ttynull_close(struct tty_struct *tty, struct file *filp)
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{
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tty_port_close(&ttynull_port, tty, filp);
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}
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static void ttynull_hangup(struct tty_struct *tty)
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{
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tty_port_hangup(&ttynull_port);
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}
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static int ttynull_write(struct tty_struct *tty, const unsigned char *buf,
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int count)
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{
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return count;
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}
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static int ttynull_write_room(struct tty_struct *tty)
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{
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return 65536;
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}
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static const struct tty_operations ttynull_ops = {
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.open = ttynull_open,
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.close = ttynull_close,
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.hangup = ttynull_hangup,
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.write = ttynull_write,
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.write_room = ttynull_write_room,
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};
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static struct tty_driver *ttynull_device(struct console *c, int *index)
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{
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*index = 0;
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return ttynull_driver;
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}
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static struct console ttynull_console = {
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.name = "ttynull",
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.device = ttynull_device,
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};
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static int __init ttynull_init(void)
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{
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struct tty_driver *driver;
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int ret;
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driver = tty_alloc_driver(1,
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TTY_DRIVER_RESET_TERMIOS |
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TTY_DRIVER_REAL_RAW |
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TTY_DRIVER_UNNUMBERED_NODE);
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if (IS_ERR(driver))
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return PTR_ERR(driver);
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tty_port_init(&ttynull_port);
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ttynull_port.ops = &ttynull_port_ops;
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driver->driver_name = "ttynull";
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driver->name = "ttynull";
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driver->type = TTY_DRIVER_TYPE_CONSOLE;
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driver->init_termios = tty_std_termios;
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driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
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tty_set_operations(driver, &ttynull_ops);
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tty_port_link_device(&ttynull_port, driver, 0);
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ret = tty_register_driver(driver);
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if (ret < 0) {
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put_tty_driver(driver);
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tty_port_destroy(&ttynull_port);
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return ret;
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}
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ttynull_driver = driver;
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register_console(&ttynull_console);
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return 0;
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}
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static void __exit ttynull_exit(void)
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{
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unregister_console(&ttynull_console);
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tty_unregister_driver(ttynull_driver);
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put_tty_driver(ttynull_driver);
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tty_port_destroy(&ttynull_port);
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}
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module_init(ttynull_init);
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module_exit(ttynull_exit);
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MODULE_LICENSE("GPL v2");
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