On Sun, Feb 16, 2025 at 11:07:47PM -0500, adamsimonelli@xxxxxxxxx wrote:
> From: Adam Simonelli <adamsimonelli@xxxxxxxxx>
>
> Add a config option CONFIG_NULL_TTY_CONSOLE that will have ttynull be
> initialized by console_initcall() and selected as a possible console
> device.
>
> Signed-off-by: Adam Simonelli <adamsimonelli@xxxxxxxxx>
> ---
> drivers/tty/Kconfig | 18 +++++++++++++++++-
> drivers/tty/ttynull.c | 16 +++++++++++++++-
> 2 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index 63a494d36a1f..afe4e7722d4c 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -383,7 +383,23 @@ 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
> + CONFIG_NULL_TTY_CONSOLE.
> +
> + If unsure, say N.
> +
> +config NULL_TTY_CONSOLE
> + bool "Supports /dev/ttynull as a console automatically"
> + 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 useful for userspace applications that expect a working
> + console device, without changing the kernel boot options, such as a
> + distribuition or environment that historically had CONFIG_VT_CONSOLE
> + enabled, and have now disabled it, but still need /dev/console to be
> + working for userspace applications.
>
> If unsure, say N.
>
> diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
> index 6b2f7208b564..8ba629ae426b 100644
> --- a/drivers/tty/ttynull.c
> +++ b/drivers/tty/ttynull.c
> @@ -57,6 +57,10 @@ static struct tty_driver *ttynull_device(struct console *c, int *index)
> static struct console ttynull_console = {
> .name = "ttynull",
> .device = ttynull_device,
> +#ifdef CONFIG_NULL_TTY_CONSOLE
> + .index = -1,
> + .flags = CON_PRINTBUFFER,
> +#endif
There's no way to do this without #ifdef in the .c files?
> };
>
> static int __init ttynull_init(void)
> @@ -90,10 +94,20 @@ static int __init ttynull_init(void)
> }
>
> ttynull_driver = driver;
> - register_console(&ttynull_console);
> + if (!console_is_registered(&ttynull_console))
> + register_console(&ttynull_console);
> +
Why do you register this twice?
> + return 0;
> +}
>
> +#ifdef CONFIG_NULL_TTY_CONSOLE
> +static int __init ttynull_register(void)
> +{
> + register_console(&ttynull_console);
Here, why is this registered again?
You should only have to do this once, and not need to check before
trying again, right?
thanks,
greg k-h
