From: Adam Simonelli <adamsimonelli@xxxxxxxxx> If CONFIG_NULL_TTY_CONSOLE is enabled, and CONFIG_VT is disabled, ttynull will become the default primary console device, based on the link order. Many distributions ship with CONFIG_VT enabled. On tested desktop hardware if CONFIG_VT is disabled, the default console device falls back to /dev/ttyS0 instead of /dev/tty. This could cause issues in user space, and hardware problems: 1. The user space issues include the case where /dev/ttyS0 is disconnected, and the TCGETS ioctl, which some user space libraries use as a probe to determine if a file is a tty, is called on /dev/console and fails. Programs that call isatty() on /dev/console and get an incorrect false value may skip expected logging to /dev/console 2. The hardware issues include the case if a user has a science instrument or other device connected to the /dev/ttyS0 port, and they were to upgrade to a kernel that is disabling the CONFIG_VT option, kernel logs will then be sent to the device connected to /dev/ttyS0 unless they edit their kernel command line manually. The new CONFIG_NULL_TTY_CONSOLE option will give users and distribution maintainers an option to avoid this. Disabling CONFIG_VT and enabling CONFIG_NULL_TTY_CONSOLE will ensure the default kernel console behavior is not dependant on hardware configuration by default, and avoid unexpected new behavior on devices connected to the /dev/ttyS0 serial port. Signed-off-by: Adam Simonelli <adamsimonelli@xxxxxxxxx> --- drivers/tty/Makefile | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile index 07aca5184a55..1fb905cfb420 100644 --- a/drivers/tty/Makefile +++ b/drivers/tty/Makefile @@ -11,6 +11,10 @@ obj-$(CONFIG_N_HDLC) += n_hdlc.o obj-$(CONFIG_N_GSM) += n_gsm.o obj-y += vt/ +# If ttynull is configured to be a console by default, ensure that it is linked +# earlier before a real one is selected. +obj-$(CONFIG_NULL_TTY_CONSOLE) += ttynull.o + obj-$(CONFIG_HVC_DRIVER) += hvc/ obj-y += serial/ obj-$(CONFIG_SERIAL_DEV_BUS) += serdev/ @@ -20,7 +24,13 @@ obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o obj-$(CONFIG_MOXA_INTELLIO) += moxa.o obj-$(CONFIG_MOXA_SMARTIO) += mxser.o obj-$(CONFIG_NOZOMI) += nozomi.o + +# If ttynull is enabled, but not as a boot console, it is linked and used later +# after the real ones. +ifneq ($(CONFIG_NULL_TTY_CONSOLE),y) obj-$(CONFIG_NULL_TTY) += ttynull.o +endif + obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o -- 2.45.2
