linux-kernel - Re: [PATCH v4 1/7] kernel: Add support for restart notifier call chain

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Date:	Mon, 14 Jul 2014 07:58:59 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Will Deacon <Will.Deacon@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Heiko Stuebner <heiko@...ech.de>,
	Russell King <linux@....linux.org.uk>,
	Jonas Jensen <jonas.jensen@...il.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Tomasz Figa <t.figa@...sung.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/7] kernel: Add support for restart notifier call
 chain

On 07/14/2014 07:53 AM, Catalin Marinas wrote:
> On Sun, Jul 13, 2014 at 04:30:25PM +0100, Guenter Roeck wrote:
>> diff --git a/include/linux/reboot.h b/include/linux/reboot.h
>> index 48bf152..120db73 100644
>> --- a/include/linux/reboot.h
>> +++ b/include/linux/reboot.h
>> @@ -38,6 +38,9 @@ extern int reboot_force;
>>   extern int register_reboot_notifier(struct notifier_block *);
>>   extern int unregister_reboot_notifier(struct notifier_block *);
>>
>> +extern int register_restart_notifier(struct notifier_block *);
>> +extern int unregister_restart_notifier(struct notifier_block *);
>> +extern void kernel_restart_notify(char *cmd);
>>
>>   /*
>>    * Architecture-specific implementations of sys_reboot commands.
>> diff --git a/kernel/reboot.c b/kernel/reboot.c
>> index a3a9e24..1bc9bf2 100644
>> --- a/kernel/reboot.c
>> +++ b/kernel/reboot.c
>> @@ -104,6 +104,87 @@ int unregister_reboot_notifier(struct notifier_block *nb)
>>   }
>>   EXPORT_SYMBOL(unregister_reboot_notifier);
>>
>> +/*
>> + *	Notifier list for kernel code which wants to be called
>> + *	to restart the system.
>> + */
>> +static BLOCKING_NOTIFIER_HEAD(restart_notifier_list);
>> +
>> +/**
>> + *	register_restart_notifier - Register function to be called to reset
>> + *				    the system
>> + *	@nb: Info about notifier function to be called
>> + *	@nb->priority:	Notifier priority. Notifiers should follow the
>> + *			following guidelines for setting priorities.
>> + *			0:	Restart notifier of last resort,
>> + *				with limited restart capabilities
>> + *			128:	Default notifier; use if no other
>> + *				notifier is expected to be available,
>> + *				and/or if restart functionality is
>> + *				sufficient to restart the entire system
>> + *			255:	Highest priority notifier, will preempt
>> + *				all other notifier functions
>
> I'm not fully convinced implying a 'notifier' is the right approach
> here. By analogy with the reboot notifier, this is something drivers
> would want to know about and do some work before the actual system
> restart (e.g. disable watchdogs as in the reboot notifier case). The
> restart notifier here is meant to perform the actual system restart.
> Arguably, the actual restart should be handled by priority 0 with some
> preparation before but we have reboot notifier already, so I don't think
> it's worth another notifier.
>
> While re-using the notifier mechanism behind the scene is fine, I think
> we should at least rename the functions to something like
> (un)register_restart_handler().
>

Fine with me. Any other comments / suggestions on the name of the function ?

Guenter


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