On Fri 2025-03-14 12:07:49, adamsimonelli@xxxxxxxxx wrote: > From: Adam Simonelli <adamsimonelli@xxxxxxxxx> > > The new option is CONFIG_NULL_TTY_DEFAULT_CONSOLE. > > if enabled, and CONFIG_VT is disabled, ttynull will become the default > primary console device. > > ttynull will be the only console device usually with this option enabled. > Some architectures do call add_preferred_console() which may add another > console though. > > Motivation: > > 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_DEFAULT_CONSOLE option will give users and > distribution maintainers an option to avoid this. Disabling CONFIG_VT and > enabling CONFIG_NULL_TTY_DEFAULT_CONSOLE will ensure the default kernel > console behavior is not dependent on hardware configuration by default, and > avoid unexpected new behavior on devices connected to the /dev/ttyS0 serial > port. > > Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> > Tested-by: Petr Mladek <pmladek@xxxxxxxx> > Signed-off-by: Adam Simonelli <adamsimonelli@xxxxxxxxx> JFYI, the patch have been comitted into printk/linux.git, branch for-6.15. Best Regards, Petr
