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

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

[Dave Young]

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@gmail.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 */

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

[Ingo Molnar]

* Dave Young <hidave.darkstar@gmail.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@gmail.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

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

[Dave Young]

On Sun, Jun 7, 2009 at 10:32 PM, Ingo Molnar<mingo@elte.hu> wrote:
>
> * Dave Young <hidave.darkstar@gmail.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@gmail.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