syslog warning: was: Re: [PATCH v6 04/11] printk: Support toggling per-console loglevel via syslog() and cmdline

[Petr Mladek <pmladek@suse.com>]

On Mon 2024-10-28 16:45:40, Chris Down wrote:
> A new module parameter (ignore_per_console_loglevel) is added, which can
> be set via the kernel command line or at runtime through
> /sys/module/printk/parameters/ignore_per_console_loglevel. When set, the
> per-console loglevels are ignored, and the global console loglevel
> (console_loglevel) is used for all consoles.
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1836,19 +1862,28 @@ int do_syslog(int type, char __user *buf, int len, int source)
>  		break;
>  	/* Disable logging to console */
>  	case SYSLOG_ACTION_CONSOLE_OFF:
> -		if (saved_console_loglevel == LOGLEVEL_DEFAULT)
> +		if (saved_console_loglevel == LOGLEVEL_DEFAULT) {
>  			saved_console_loglevel = console_loglevel;
> +			saved_ignore_per_console_loglevel =
> +				ignore_per_console_loglevel;
> +		}
>  		console_loglevel = minimum_console_loglevel;
> +		ignore_per_console_loglevel = true;
>  		break;
>  	/* Enable logging to console */
>  	case SYSLOG_ACTION_CONSOLE_ON:
>  		if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
>  			console_loglevel = saved_console_loglevel;
> +			ignore_per_console_loglevel =
> +				saved_ignore_per_console_loglevel;
>  			saved_console_loglevel = LOGLEVEL_DEFAULT;
>  		}
>  		break;
>  	/* Set level of messages printed to console */
>  	case SYSLOG_ACTION_CONSOLE_LEVEL:
> +		if (!ignore_per_console_loglevel)
> +			pr_warn_once(
> +				"SYSLOG_ACTION_CONSOLE_LEVEL is ignored by consoles with an explicitly set per-console loglevel, see Documentation/admin-guide/per-console-loglevel.rst\n");

I see this warning during every boot because rsyslogd() modifies the
global loglevel.

I am afraid that admins might not like it. I might live in dreams but
I guess that everyone would like to reach a clean boot without any
warning.

One the other hand, we should warn when it does not work as expected.

A compromise would be to warn only when there is a console with
the console specific loglevel set.

I am not sure if we have already discussed this in the past.
But I would prefer the compromise after all.

What do you think, please?

Best Regards,
Petr