linux-kernel - Re: [PATCH v2 1/3] printk: introduce new macros pr_<level>

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Message-ID: <Y4dndyIiosT7l4RG@alley>
Date:   Wed, 30 Nov 2022 15:23:51 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Weißschuh <linux@...ssschuh.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        linux-pm@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Whitcroft <apw@...onical.com>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH v2 1/3] printk: introduce new macros pr_<level>_cont()

On Fri 2022-11-25 20:09:46, Thomas Weißschuh wrote:
> These macros emit continuation messages with explicit levels.
> In case the continuation is logged separately from the original message
> it will retain its level instead of falling back to KERN_DEFAULT.
> 
> This remedies the issue that logs filtered by level contain stray
> continuation messages without context.
> 
> Suggested-by: Petr Mladek <pmladek@...e.com>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  include/linux/printk.h | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 8c81806c2e99..8f564c38f121 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -537,6 +537,8 @@ struct pi_entry {
>   * This macro expands to a printk with KERN_CONT loglevel. It should only be
>   * used when continuing a log message with no newline ('\n') enclosed. Otherwise
>   * it defaults back to KERN_DEFAULT loglevel.
> + *
> + * Use the dedicated pr_<level>_cont() macros instead.
>   */
>  #define pr_cont(fmt, ...) \
>  	printk(KERN_CONT fmt, ##__VA_ARGS__)
> @@ -701,6 +703,27 @@ do {									\
>  	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
>  #endif
>  
> +/*
> + * Print a continuation message with level. In case the continuation is split
> + * from the main message it preserves the level.
> + */
> +
> +#define pr_emerg_cont(fmt, ...)					\
> +	printk(KERN_EMERG KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_alert_cont(fmt, ...)					\
> +	printk(KERN_ALERT KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_crit_cont(fmt, ...)					\
> +	printk(KERN_CRIT KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_err_cont(fmt, ...)					\
> +	printk(KERN_ERR KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_warn_cont(fmt, ...)					\
> +	printk(KERN_WARN KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_notice_cont(fmt, ...)					\
> +	printk(KERN_NOTICE KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +#define pr_info_cont(fmt, ...)					\
> +	printk(KERN_INFO KERN_CONT pr_fmt(fmt), ##__VA_ARGS__)
> +/* no pr_debug_ratelimited, it doesn't make sense with CONFIG_DYNAMIC_DEBUG. */

I guess that you wanted to write "pr_debug_cont".

Also I am not sure what you mean with "doesn't make sense". IMHO, it
might  make sense. But it would be hard to use and error prone
with CONFIG_DYNAMIC_DEBUG.

And more importantly, it probably would not work properly. If I get
it corretly the dynamic debug messages are printed by the wrapper:

void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
{
[...]
	vaf.fmt = fmt;
	vaf.va = &args;

	printk(KERN_DEBUG "%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf);
[...]

This clearly does not support KERN_CONT in "fmt".

I suggest to either remove the comment completely. Or write something
like:

/* no pr_debug_cont(), can't be supported easily with CONFIG_DYNAMIC_DEBUG */


Best Regards,
Petr