linux-kernel - Re: [PATCH] printk: allow setting DEFAULT_MESSAGE

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Date:	Wed, 26 Jan 2011 14:57:03 -0800
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	olofj@...omium.org
Subject: Re: [PATCH] printk: allow setting DEFAULT_MESSAGE_LEVEL via Kconfig

On Wed, 26 Jan 2011 14:49:10 -0800 Andrew Morton wrote:

> On Tue, 25 Jan 2011 15:57:00 -0800
> Mandeep Singh Baines <msb@...omium.org> wrote:
> 
> > We've been burned by regressions/bugs which we later realized could
> > have been triaged quicker if only we'd paid closer attention to
> > dmesg. To make it easier to audit dmesg, we'd like to make
> > DEFAULT_MESSAGE_LEVEL Kconfig-settable. That way we can set it to
> > KERN_NOTICE and audit any messages <= KERN_WARNING.
> > 
> > Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
> > ---
> >  kernel/printk.c   |    2 +-
> >  lib/Kconfig.debug |   12 ++++++++++++
> >  2 files changed, 13 insertions(+), 1 deletions(-)
> > 
> > diff --git a/kernel/printk.c b/kernel/printk.c
> > index 5ddd291..f91a7fd 100644
> > --- a/kernel/printk.c
> > +++ b/kernel/printk.c
> > @@ -59,7 +59,7 @@ void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
> >  #define __LOG_BUF_LEN	(1 << CONFIG_LOG_BUF_SHIFT)
> >  
> >  /* printk's without a loglevel use this.. */
> > -#define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
> > +#define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL
> >  
> >  /* We show everything that is MORE important than this.. */
> >  #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 28b42b9..67b42fa 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -9,6 +9,18 @@ config PRINTK_TIME
> >  	  operations.  This is useful for identifying long delays
> >  	  in kernel startup.
> >  
> > +config DEFAULT_MESSAGE_LOGLEVEL
> > +	int "Default message log level (1-7)"
> > +	range 1 7
> > +	depends on PRINTK
> > +	default "4"
> > +	help
> > +	  Default log level for printk statements with no specified priority.
> > +
> > +	  This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
> > +	  that are auditing their logs closely may want to set it to a lower
> > +	  priority.
> > +
> >  config ENABLE_WARN_DEPRECATED
> >  	bool "Enable __deprecated logic"
> >  	default y
> 
> I'm a bit surprised that this wasn't already tunable at boot-time
> and/or at runtime.


As WANG Cong replied:

Why? We already have "loglevel=" kernel parameter.


> I think it's generally superior to be able to tune this sort of thing
> via kernel boot parameters and/or /proc knobs, rather than requiring a
> recompile.  That might be a problem in this specific case, if we have
> printks which are occurring before __setup() parsing has completed.
> 
> 
> Poeple often complain that they want things settable in Kconfig because
> for some reason it's all too hard to set the kernel boot command line. 
> Next time someone says this I'll suggest that they fix the problem
> permanently by implementing a CONFIG_CMDLINE string, which gets
> inserted into the kernel boot command line at compile time ;)


---
~Randy
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