printk: add printk_delay to make messages readable for some scenarios

When syslog is not possible, at the same time there's no serial/net
console available, it will be hard to read the printk messages.  For
example oops/panic/warning messages in shutdown phase.

Add a printk delay feature, we can make each printk message delay some
milliseconds.

Setting the delay by proc/sysctl interface: /proc/sys/kernel/printk_delay

The value range from 0 - 10000, default value is 0

[akpm@linux-foundation.org: fix a few things]
Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2b5b1e0899a8..0a2a19087863 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -246,6 +246,8 @@ extern int printk_ratelimit(void);
 extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
                                    unsigned int interval_msec);
 
+extern int printk_delay_msec;
+
 /*
  * Print a one-time message (analogous to WARN_ONCE() et al):
  */