linux-kernel - [PATCH v2] printk: add halt_delay parameter for printk delay in halt phase

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Date:	Wed, 3 Jun 2009 11:09:27 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH v2] printk: add halt_delay parameter for printk delay in halt 
	phase

Add a halt_delay module parameter in printk.c used to read the printk
messages in halt/poweroff/restart phase, delay each printk messages
by halt_delay milliseconds. It is useful for debugging if there's no
other way to dump kernel messages that time.

The halt_delay max value is 65535, default value is 0, change it by:

echo xxx > /sys/module/printk/parameters/halt_delay

Signed-off-by: Dave Young <hidave.darkstar@...il.com>
---
kernel/printk.c |   16 ++++++++++++++++
1 file changed, 16 insertions(+)

--- linux-2.6.orig/kernel/printk.c	2009-06-03 10:16:55.000000000 +0800
+++ linux-2.6/kernel/printk.c	2009-06-03 10:32:43.000000000 +0800
@@ -250,6 +250,22 @@ static inline void boot_delay_msec(void)
 }
 #endif

+/* msecs delay after each halt/poweroff/restart phase printk,
+unsigned short is enough for delay in milliseconds */
+static unsigned short halt_delay;
+
+static inline void halt_delay_msec(void)
+{
+	if (unlikely(halt_delay == 0 || !(system_state == SYSTEM_HALT
+				|| system_state == SYSTEM_POWER_OFF
+				|| system_state == SYSTEM_RESTART)))
+		return;
+
+	mdelay(halt_delay);
+}
+
+module_param(halt_delay, ushort, S_IRUGO | S_IWUSR);
+
 /*
  * Commands to do_syslog:
  *
@@ -649,6 +665,7 @@ asmlinkage int vprintk(const char *fmt,
 	char *p;

 	boot_delay_msec();
+	halt_delay_msec();

 	preempt_disable();
 	/* This stops the holder of console_sem just where we want him */
--
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