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

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Message-ID: <Y4nvSTTPdSEIZ+zl@alley>
Date:   Fri, 2 Dec 2022 13:27:53 +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 Wed 2022-11-30 15:56:33, Thomas Weißschuh wrote:
> On 2022-11-30 15:23+0100, Petr Mladek wrote:
> > 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".
> 
> Indeed.
> 
> > 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".
> 
> Good point.
> 
> My doubt was more that it would force users to know which message
> continuations belong together and always enable all of them together with
> dynamic debug.
> Which would be very errorprone and annoying to use.

Yes. This is what I meant with "hard to use" but I was not clear
enough :-)

> 
> But if it doesn't work at all that's an even stronger point.
> 
> > 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 */
> 
> What about:
> 
> /* no pr_debug_cont(), it's errorprone to use
>  * and can't be supported easily with CONFIG_DYNAMIC_DEBUG */

Sounds good to me.

Best Regards,
Petr

PS: Heh, I just realized that we actually abandoned these changes because
    the continuous lines in kernel/power/process.c are going to be
    removed. (/me doing too many things in parallel).

    Anyway, it is possible that someone would take this patches to fix
    another continuous lines in the future.