[patch] add ignore_loglevel boot option

[patch] add ignore_loglevel boot option

[Ingo Molnar]

Subject: [patch] add ignore_loglevel boot option
From: Ingo Molnar <mingo@elte.hu>

sometimes the kernel prints something interesting while userspace
bootup keeps messages turned off via loglevel. Enable the printing
of /all/ kernel messages via the "ignore_loglevel" boot option.
Off by default.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 Documentation/kernel-parameters.txt |    4 ++++
 kernel/printk.c                     |   14 +++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

Index: linux/Documentation/kernel-parameters.txt
===================================================================
--- linux.orig/Documentation/kernel-parameters.txt
+++ linux/Documentation/kernel-parameters.txt
@@ -657,6 +657,10 @@ and is between 256 and 4096 characters. 
 	idle=		[HW]
 			Format: idle=poll or idle=halt
 
+	ignore_loglevel	[KNL]
+			Ignore loglevel setting - this will print /all/
+			kernel messages to the console. Useful for debugging.
+
 	ihash_entries=	[KNL]
 			Set number of hash buckets for inode cache.
 
Index: linux/kernel/printk.c
===================================================================
--- linux.orig/kernel/printk.c
+++ linux/kernel/printk.c
@@ -352,13 +352,25 @@ static void __call_console_drivers(unsig
 	touch_critical_timing();
 }
 
+static int __read_mostly ignore_loglevel;
+
+int __init ignore_loglevel_setup(char *str)
+{
+	ignore_loglevel = 1;
+	printk(KERN_INFO "debug: ignoring loglevel setting.\n");
+
+	return 1;
+}
+
+__setup("ignore_loglevel", ignore_loglevel_setup);
+
 /*
  * Write out chars from start to end - 1 inclusive
  */
 static void _call_console_drivers(unsigned long start,
 				unsigned long end, int msg_log_level)
 {
-	if (msg_log_level < console_loglevel &&
+	if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 			console_drivers && start != end) {
 		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 			/* wrapped write */

Re: [patch] add ignore_loglevel boot option

[Randy Dunlap]

On Tue, 5 Dec 2006 13:09:54 +0100 Ingo Molnar wrote:

> Subject: [patch] add ignore_loglevel boot option
> From: Ingo Molnar <mingo@elte.hu>
> 
> sometimes the kernel prints something interesting while userspace
> bootup keeps messages turned off via loglevel. Enable the printing
> of /all/ kernel messages via the "ignore_loglevel" boot option.
> Off by default.

Hi,

Is this equivalent to using the "debug" kernel parameter
except that userspace (init scripts) cannot muck it up (modify
the setting)?

I've seen init scripts modify the loglevel, much to my
dismay.

I'd say that this is useful, but it's really userspace
that needs to be fixed.

> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
>  Documentation/kernel-parameters.txt |    4 ++++
>  kernel/printk.c                     |   14 +++++++++++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> Index: linux/kernel/printk.c
> ===================================================================
> --- linux.orig/kernel/printk.c
> +++ linux/kernel/printk.c
> @@ -352,13 +352,25 @@ static void __call_console_drivers(unsig
>  	touch_critical_timing();
>  }
>  
> +static int __read_mostly ignore_loglevel;
> +
> +int __init ignore_loglevel_setup(char *str)
> +{
> +	ignore_loglevel = 1;
> +	printk(KERN_INFO "debug: ignoring loglevel setting.\n");
> +
> +	return 1;
> +}
> +
> +__setup("ignore_loglevel", ignore_loglevel_setup);
> +
>  /*
>   * Write out chars from start to end - 1 inclusive
>   */
>  static void _call_console_drivers(unsigned long start,
>  				unsigned long end, int msg_log_level)
>  {
> -	if (msg_log_level < console_loglevel &&
> +	if ((msg_log_level < console_loglevel || ignore_loglevel) &&
>  			console_drivers && start != end) {
>  		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
>  			/* wrapped write */
> -

---
~Randy

Re: [patch] add ignore_loglevel boot option

[Ingo Molnar]

* Randy Dunlap <randy.dunlap@oracle.com> wrote:

> > sometimes the kernel prints something interesting while userspace 
> > bootup keeps messages turned off via loglevel. Enable the printing 
> > of /all/ kernel messages via the "ignore_loglevel" boot option. Off 
> > by default.
> 
> Hi,
> 
> Is this equivalent to using the "debug" kernel parameter except that 
> userspace (init scripts) cannot muck it up (modify the setting)?

yeah.

> I've seen init scripts modify the loglevel, much to my dismay.

yeah - i once lost a few hours of debugging to such an incident.

> I'd say that this is useful, but it's really userspace that needs to 
> be fixed.

well, loglevel /can/ be managed by userspace, and sometimes an important 
kernel message might have a too high loglevel. Also, sometimes the 
kernel does spurious messages during hardware detect, etc., so userspace 
naturally wants to prevent them from going to the console. So it's 
really a mix of a problem and i wouldnt put the blame on user-space. 
User-space used the only control they have to fix the situation.

	Ingo