linux-kernel - Re: [PATCH v2] leds: heartbeat: stop on shutdown

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Date:	Tue, 24 Apr 2012 18:32:10 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	shuahkhan@...il.com
CC:	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] leds: heartbeat: stop on shutdown

Am 24.04.2012 17:24, schrieb Shuah Khan:
> On Tue, 2012-04-24 at 17:07 +0200, Alexander Holler wrote:
>> A halted kernel should not show a heartbeat.
>>
>> Signed-off-by: Alexander Holler <holler@...oftware.de>
>> ---
>>  drivers/leds/ledtrig-heartbeat.c |   18 +++++++++++++++++-
>>  1 files changed, 17 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/leds/ledtrig-heartbeat.c b/drivers/leds/ledtrig-heartbeat.c
>> index 759c0bb..1c05bd9 100644
>> --- a/drivers/leds/ledtrig-heartbeat.c
>> +++ b/drivers/leds/ledtrig-heartbeat.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/timer.h>
>>  #include <linux/sched.h>
>>  #include <linux/leds.h>
>> +#include <linux/reboot.h>
>>  #include "leds.h"
>>  
>>  struct heartbeat_trig_data {
>> @@ -101,13 +102,28 @@ static struct led_trigger heartbeat_led_trigger = {
>>  	.deactivate = heartbeat_trig_deactivate,
>>  };
>>  
>> +static int heartbeat_reboot_notifier(struct notifier_block *nb,
>> +				     unsigned long code, void *unused)
>> +{
>> +	led_trigger_unregister(&heartbeat_led_trigger);
>> +	return NOTIFY_DONE;
>> +}
>> +
>> +static struct notifier_block heartbeat_reboot_nb = {
>> +	.notifier_call = heartbeat_reboot_notifier,
>> +};
>> +
>>  static int __init heartbeat_trig_init(void)
>>  {
>> -	return led_trigger_register(&heartbeat_led_trigger);
>> +	int rc = led_trigger_register(&heartbeat_led_trigger);
>> +	if( ! rc )
>> +		register_reboot_notifier(&heartbeat_reboot_nb);
> 
> Do you need to check return value here? I see return value being checked
> in some places in the kernel and not in others. Not checking is fine for
> now since register_reboot_notifier() always returns 0.
> 
> Maybe adding return handling might not be a bad idea to be consistent
> with other places that do check.

What to do if it fails? As long as unregister_reboot_notifier() doesn't
do something bad with non-registered notifiers (which it doesn't), I
would let the init still succeed. And to not unregister a
non-registered-reboot_notifier, a long-living bool would be needed.

> FYI - Andrew Morton is handling led patches these days. You might want
> to send include him  <akpm@...ux-foundation.org>

I have added him to CC, thanks.

Regards,

Alexander
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