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

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Date:	Mon, 8 Jun 2009 15:29:30 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On Sun, Jun 7, 2009 at 10:32 PM, Ingo Molnar<mingo@...e.hu> wrote:
>
> * 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.

Oops, will add in v3

>
> Thanks,
>
>        Ingo
>



-- 
Regards
dave
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