linux-kernel - Re: [PATCH 7/7] [RFC] APM emulation driver for class batteries

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Date:	Tue, 17 Apr 2007 01:08:29 +0400
From:	Anton Vorontsov <cbou@...l.ru>
To:	linux-kernel@...r.kernel.org, kernel-discuss@...dhelds.org
Subject: Re: [PATCH 7/7] [RFC] APM emulation driver for class batteries

On Mon, Apr 16, 2007 at 09:24:21PM +0100, Russell King wrote:
> On Fri, Apr 13, 2007 at 05:50:43PM +0400, Anton Vorontsov wrote:
> > +static void (*old_apm_get_power_status)(struct apm_power_info*);
> > +
> > +static int __init apm_battery_init(void)
> > +{
> > +	printk(KERN_INFO "APM Battery Driver\n");
> > +
> > +	old_apm_get_power_status = apm_get_power_status;
> > +	apm_get_power_status = apm_battery_apm_get_power_status;
> > +	return 0;
> > +}
> > +
> > +static void __exit apm_battery_exit(void)
> > +{
> > +	apm_get_power_status = old_apm_get_power_status;
> > +	return;
> > +}
> 
> Utterly unsafe.  What happens if some other module gets loaded which
> does this, and then this module is unloaded followed by the other
> module.  Result: Oops.

Right. And loading two modules which changing apm_get_power_status
is a race already. Thus, APM interface needs a mutex.

Or pda_power should be marked "bool" in Kconfig, as it is done
in arch/arm/common/sharpsl_pm.c. Sharpsl_pm is safe only because it
can't be a module.

Personally I'd keep things as is for now (i.e. I'd want tristate for
PDA_POWER, not bool). Later APM API can be fixed.

> -- 
> Russell King
>  Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
>  maintainer of:
> -
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> 

Thanks,

-- 
Anton Vorontsov
email: cbou@...l.ru
backup email: ya-cbou@...dex.ru
irc://irc.freenode.org/bd2
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