[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: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 17 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2a40d9f6ffad..6b3c3e37a277 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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.
 
diff --git a/kernel/printk.c b/kernel/printk.c
index c3d90a58e4c5..185bb45eacf7 100644
--- a/kernel/printk.c
+++ b/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 */