| Message ID | 20250311033133.1859963-3-adamsimonelli@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | Optionally allow ttynull to be selected as a default console | expand |
On Mon 2025-03-10 23:31:31, adamsimonelli@gmail.com wrote: > From: Adam Simonelli <adamsimonelli@gmail.com> > > The new config option, CONFIG_NULL_TTY_DEFAULT_CONSOLE will allow > ttynull to be initialized by console_initcall() and selected as a > possible console device. It would be great to mention here the motivation. It is nicely explained in the 3rd patch. > --- a/drivers/tty/Kconfig > +++ b/drivers/tty/Kconfig > @@ -383,7 +383,20 @@ config NULL_TTY > available or desired. > > In order to use this driver, you should redirect the console to this > - TTY, or boot the kernel with console=ttynull. > + TTY, boot the kernel with console=ttynull, or enable > + NULL_TTY_DEFAULT_CONSOLE. > + > + If unsure, say N. > + > +config NULL_TTY_DEFAULT_CONSOLE > + bool "Support for console on ttynull" > + depends on NULL_TTY=y && !VT_CONSOLE > + help > + Say Y here if you want the NULL TTY to be used as a /dev/console > + device. I would provide few more details, something like: <proposal> Say Y here if you want the NULL TTY to be used as a /dev/console device by default. For example, it might be useful to prevent a VT-less kernel from writing the system log to a random device connected to the serial port. Another console driver still might get preferred via the command line, SPCR, or the device tree. </proposal> > + This is similar to VT_CONSOLE, but without the dependency on VT. > + It uses the ttynull driver as the system console. Honestly, I do not find this paragraph much useful. I would omit it, > If unsure, say N. > > diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c > index d8b51edde628..67aad3e6f538 100644 > --- a/drivers/tty/ttynull.c > +++ b/drivers/tty/ttynull.c > @@ -96,6 +96,19 @@ static int __init ttynull_init(void) > return 0; > } > > +#ifdef CONFIG_NULL_TTY_DEFAULT_CONSOLE > +static int __init ttynull_register(void) > +{ > + if (console_set_on_cmdline) > + return 0; > + > + add_preferred_console("ttynull", 0, NULL); > + > + return 0; > +} > +console_initcall(ttynull_register); > +#endif I have realized that this does not work without shuffling the linking order (3rd patch). I would prefer to avoid the linking order hack and rather call this in console_init() directly, see https://lore.kernel.org/r/Z9GPVVTnngGbmbuv@pathway.suse.cz for more details. Best Regards, Petr
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index 63a494d36a1f..edf557c73586 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -383,7 +383,20 @@ config NULL_TTY available or desired. In order to use this driver, you should redirect the console to this - TTY, or boot the kernel with console=ttynull. + TTY, boot the kernel with console=ttynull, or enable + NULL_TTY_DEFAULT_CONSOLE. + + If unsure, say N. + +config NULL_TTY_DEFAULT_CONSOLE + bool "Support for console on ttynull" + depends on NULL_TTY=y && !VT_CONSOLE + help + Say Y here if you want the NULL TTY to be used as a /dev/console + device. + + This is similar to VT_CONSOLE, but without the dependency on VT. + It uses the ttynull driver as the system console. If unsure, say N. diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c index d8b51edde628..67aad3e6f538 100644 --- a/drivers/tty/ttynull.c +++ b/drivers/tty/ttynull.c @@ -96,6 +96,19 @@ static int __init ttynull_init(void) return 0; } +#ifdef CONFIG_NULL_TTY_DEFAULT_CONSOLE +static int __init ttynull_register(void) +{ + if (console_set_on_cmdline) + return 0; + + add_preferred_console("ttynull", 0, NULL); + + return 0; +} +console_initcall(ttynull_register); +#endif + static void __exit ttynull_exit(void) { unregister_console(&ttynull_console);