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

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Date:	Sun, 7 Jun 2009 16:32:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] printk: add halt_delay parameter for printk delay
	in halt phase


* Dave Young <hidave.darkstar@...il.com> wrote:

> 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 */

Looks nice now - but please also add a description to 
Documentation/kernel-parameters.txt.

Thanks,

	Ingo
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