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authorVincent Whitchurch <vincent.whitchurch@axis.com>2019-04-03 13:33:27 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-04-16 15:21:34 +0200
commit3117ff13f104e98b05b61e19cc754d1377e92e15 (patch)
tree466a0a4bb36d0786128d170bcb43f60e40c2c918 /drivers/tty
parent89bb1e1ee529d9d06ca694ba22a35dc2a3d6ac67 (diff)
tty: Add NULL TTY driver
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>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/Kconfig14
-rw-r--r--drivers/tty/Makefile1
-rw-r--r--drivers/tty/ttynull.c109
3 files changed, 124 insertions, 0 deletions
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 0ebb8d6ab341..80f65767aacf 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -374,6 +374,20 @@ config PPC_EARLY_DEBUG_EHV_BC_HANDLE
there simply will be no early console output. This is true also
if you don't boot under a hypervisor at all.
+config NULL_TTY
+ tristate "NULL TTY driver"
+ help
+ Say Y here if you want a NULL TTY which simply discards messages.
+
+ This is useful to allow userspace applications which expect a console
+ device to work without modifications even when no console is
+ available or desired.
+
+ In order to use this driver, you should redirect the console to this
+ TTY, or boot the kernel with console=ttynull.
+
+ If unsure, say N.
+
config GOLDFISH_TTY
tristate "Goldfish TTY Driver"
depends on GOLDFISH
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index c72cafdf32b4..020b1cd9294f 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_ISI) += isicom.o
obj-$(CONFIG_MOXA_INTELLIO) += moxa.o
obj-$(CONFIG_MOXA_SMARTIO) += mxser.o
obj-$(CONFIG_NOZOMI) += nozomi.o
+obj-$(CONFIG_NULL_TTY) += ttynull.o
obj-$(CONFIG_ROCKETPORT) += rocket.o
obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o
obj-$(CONFIG_SYNCLINKMP) += synclinkmp.o
diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
new file mode 100644
index 000000000000..17f05b7eb6d3
--- /dev/null
+++ b/drivers/tty/ttynull.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 Axis Communications AB
+ *
+ * Based on ttyprintk.c:
+ * Copyright (C) 2010 Samo Pogacnik
+ */
+
+#include <linux/console.h>
+#include <linux/module.h>
+#include <linux/tty.h>
+
+static const struct tty_port_operations ttynull_port_ops;
+static struct tty_driver *ttynull_driver;
+static struct tty_port ttynull_port;
+
+static int ttynull_open(struct tty_struct *tty, struct file *filp)
+{
+ return tty_port_open(&ttynull_port, tty, filp);
+}
+
+static void ttynull_close(struct tty_struct *tty, struct file *filp)
+{
+ tty_port_close(&ttynull_port, tty, filp);
+}
+
+static void ttynull_hangup(struct tty_struct *tty)
+{
+ tty_port_hangup(&ttynull_port);
+}
+
+static int ttynull_write(struct tty_struct *tty, const unsigned char *buf,
+ int count)
+{
+ return count;
+}
+
+static int ttynull_write_room(struct tty_struct *tty)
+{
+ return 65536;
+}
+
+static const struct tty_operations ttynull_ops = {
+ .open = ttynull_open,
+ .close = ttynull_close,
+ .hangup = ttynull_hangup,
+ .write = ttynull_write,
+ .write_room = ttynull_write_room,
+};
+
+static struct tty_driver *ttynull_device(struct console *c, int *index)
+{
+ *index = 0;
+ return ttynull_driver;
+}
+
+static struct console ttynull_console = {
+ .name = "ttynull",
+ .device = ttynull_device,
+};
+
+static int __init ttynull_init(void)
+{
+ struct tty_driver *driver;
+ int ret;
+
+ driver = tty_alloc_driver(1,
+ TTY_DRIVER_RESET_TERMIOS |
+ TTY_DRIVER_REAL_RAW |
+ TTY_DRIVER_UNNUMBERED_NODE);
+ if (IS_ERR(driver))
+ return PTR_ERR(driver);
+
+ tty_port_init(&ttynull_port);
+ ttynull_port.ops = &ttynull_port_ops;
+
+ driver->driver_name = "ttynull";
+ driver->name = "ttynull";
+ driver->type = TTY_DRIVER_TYPE_CONSOLE;
+ driver->init_termios = tty_std_termios;
+ driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
+ tty_set_operations(driver, &ttynull_ops);
+ tty_port_link_device(&ttynull_port, driver, 0);
+
+ ret = tty_register_driver(driver);
+ if (ret < 0) {
+ put_tty_driver(driver);
+ tty_port_destroy(&ttynull_port);
+ return ret;
+ }
+
+ ttynull_driver = driver;
+ register_console(&ttynull_console);
+
+ return 0;
+}
+
+static void __exit ttynull_exit(void)
+{
+ unregister_console(&ttynull_console);
+ tty_unregister_driver(ttynull_driver);
+ put_tty_driver(ttynull_driver);
+ tty_port_destroy(&ttynull_port);
+}
+
+module_init(ttynull_init);
+module_exit(ttynull_exit);
+
+MODULE_LICENSE("GPL v2");