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>

1 files changed, 14 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