linux-kernel - Re: [RFC] printk: More consistent loglevel for continuous lines

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Date:   Thu, 25 Nov 2021 09:53:49 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] printk: More consistent loglevel for continuous lines

On (21/11/24 16:48), Petr Mladek wrote:
> 
> Anyway, it looks a bit non-practical to update all existing pr_cont()
> callers:
> 
> 	$> git grep "pr_cont" | wc -l
> 	2054

Another question is how many pr_cont()-s are getting compiled with
the "average" production kernel config. A number of pr_cont() is in
debugging code - lockdep, kasan, etc. - which is not compiled for prod.

[..]

> +static void printk_write_loglevel_ctx(int loglevel)
> +{
> +	u8 *loglevel_var = printk_loglevel_ctx_var();
> +
> +	if (!loglevel_var)
> +		return;
> +
> +	/*
> +	 * Remember only the really used loglevels that can be stored
> +	 * within 3 bytes in struct printk_info.
> +	 */
> +	if (WARN_ON_ONCE(loglevel != LOG_LEVEL(loglevel)))
> +		return;
> +
> +	*loglevel_var = loglevel;
> +}
> +
> +static u8 printk_read_loglevel_ctx(void)
> +{
> +	u8 *loglevel_var = printk_loglevel_ctx_var();
> +
> +	if (!loglevel_var)
> +		return LOGLEVEL_DEFAULT;
> +
> +	return *loglevel_var;
> +}
> +
>  /**
>   * printk_parse_prefix - Parse level and control flags.
>   *
> @@ -2066,6 +2122,21 @@ u16 printk_parse_prefix(const char *text, int *level,
>  	return prefix_len;
>  }
>  
> +static int printk_sanitize_loglevel(int loglevel, enum printk_info_flags flags)
> +{
> +	/* For continuous lines, fallback to the previously used loglevel. */
> +	if (flags & LOG_CONT && loglevel == LOGLEVEL_DEFAULT)
> +		loglevel = printk_read_loglevel_ctx();
> +
> +	if (loglevel == LOGLEVEL_DEFAULT)
> +		loglevel = default_message_loglevel;
> +
> +	/* Remember the really used loglevel for this context. */
> +	printk_write_loglevel_ctx(loglevel);
> +
> +	return loglevel;
> +}

Let's assume something like this

	foo()
	{
		char *s;

		pr_cont("Blah ");
		s = arch_foo();
		pr_cont("%s \n", s);
	}

Suppose that arch_foo() errs and pr_warn()-s. Are we going to use WARN
level for trailing pr_cont()?

	pr_cont("Blah ") -> printk_write_loglevel_ctx(default)
	pr_warn() -> printk_write_loglevel_ctx(warn)
	pr_cont("%s \n"") <- printk_read_loglevel_ctx(warn)



p.s. I'm still reading amazingly detailed commit messages from your console
registration patch set.