On Tuesday, March 4, 2025 1:51:52 AM EST Andy Shevchenko wrote: > On Tue, Mar 4, 2025 at 5:55 AM <adamsimonelli@xxxxxxxxx> wrote: > > > > From: Adam Simonelli <adamsimonelli@xxxxxxxxx> > > > > If CONFIG_NULL_TTY_DEFAULT_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 > > Missing period at the end. > > > 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. > > ... > > > obj-y += vt/ > > + blank line. > > > +# If ttynull is configured to be a console by default, ensure that it is linked > > +# earlier before a real one is selected. > > +obj-$(CONFIG_NULL_TTY_DEFAULT_CONSOLE) \ > > + += ttynull.o > > Here is the question: are you sure that all console drivers that exist > in the kernel happen to be here? Have you grepped the source tree for > checking this? > Grepping for console_initcall, the only other places I see outside of drivers/tty/ is arch/mips/fw/arc/arc_con.c arch/mips/sibyte/common/cfe_console.c arch/powerpc/kernel/legacy_serial.c arch/powerpc/kernel/udbg.c arch/powerpc/platforms/powermac/setup.c arch/um/drivers/stderr_console.c arch/xtensa/platforms/iss/console.c drivers/s390/char/con3215.c drivers/s390/char/con3270.c drivers/s390/char/sclp_con.c drivers/s390/char/sclp_vt220.c > ... > > > +# If ttynull is enabled, but not as a boot console, it is linked and used later > > +# after the real ones. > > +ifneq ($(CONFIG_NULL_TTY_DEFAULT_CONSOLE),y) > > Also can be written as > ifeq ($(...),) > but it might be less explicit. Up to you. > > > obj-$(CONFIG_NULL_TTY) += ttynull.o > > +endif > >
