[PATCH] add ignore_loglevel boot option

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: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Documentation/kernel-parameters.txt

@@ -650,6 +650,10 @@ and is between 256 and 4096 characters. It is defined in the file
 	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.
 

kernel/printk.c

@@ -333,13 +333,25 @@ static void __call_console_drivers(unsigned long start, unsigned long end)
 	}
 }
 
+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 */