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

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Message-ID: <Y4dhs1G3mcX/YraJ@alley>
Date:   Wed, 30 Nov 2022 14:59:15 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Weißschuh <linux@...ssschuh.net>
Cc:     Joe Perches <joe@...ches.com>,
        "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>,
        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 21:33:40, Thomas Weißschuh wrote:
> On 2022-11-25 12:18-0800, Joe Perches wrote:
> > On Fri, 2022-11-25 at 20:09 +0100, 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.
> >> 
> >> --- a/include/linux/printk.h
> >> +++ b/include/linux/printk.h
> >> @@ -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__)
> > 
> > Aren't this rather backwards?
> > KERN_CONT KERN_<LEVEL> seems to make more sense to me.
> 
> If nobody else disagrees I'll do this for v3.

I slightly prefer the way how it is now. IMHO, it makes it easier
to check the related levels in /sys/kernel/debug/printk/index/vmlinux [*]:

<6> kernel/power/process.c:227 thaw_kernel_threads "Restarting kernel threads ... "
<6,c> kernel/power/process.c:218 thaw_processes "done.\n"
<6> kernel/power/process.c:197 thaw_processes "Restarting tasks ... "
<6,c> kernel/power/process.c:176 freeze_kernel_threads "\n"
<6,c> kernel/power/process.c:174 freeze_kernel_threads "done."
<6> kernel/power/process.c:169 freeze_kernel_threads "Freezing remaining freezable tasks ... "
<6,c> kernel/power/process.c:140 freeze_processes "\n"
<6,c> kernel/power/process.c:138 freeze_processes "done."
<6> kernel/power/process.c:133 freeze_processes "Freezing user space processes ... "
<6,c> kernel/power/process.c:105 try_to_freeze_tasks "(elapsed %d.%03d seconds) "

That said, I do not want to fight over it. It is hidden behind the
API. The only really visible place is the printk index.

[*] The index is available only when CONFIG_PRINTK_INDEX is enabled.

Best Regards,
Petr