linux-kernel - Re: [PATCH v4 7/7] arm/arm64: Unexport restart handlers

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Message-ID: <20140714150909.GF1112@arm.com>
Date:	Mon, 14 Jul 2014 16:09:09 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Guenter Roeck <linux@...ck-us.net>
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 7/7] arm/arm64: Unexport restart handlers

On Mon, Jul 14, 2014 at 03:39:38PM +0100, Guenter Roeck wrote:
> On 07/14/2014 07:22 AM, Catalin Marinas wrote:
> > On Sun, Jul 13, 2014 at 04:30:31PM +0100, Guenter Roeck wrote:
> >> Implementing a restart handler in a module don't make sense
> >> as there would be no guarantee that the module is loaded when
> >> a restart is needed. Unexport arm_pm_restart to ensure that
> >> no one gets the idea to do it anyway.
> >>
> >> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> >> ---
> >> v4: No change
> >> v3: No change
> >> v2: No change
> >>
> >>   arch/arm/kernel/process.c   | 1 -
> >>   arch/arm64/kernel/process.c | 1 -
> >>   2 files changed, 2 deletions(-)
> >>
> >> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> >> index 5d191e3..25c7f00 100644
> >> --- a/arch/arm/kernel/process.c
> >> +++ b/arch/arm/kernel/process.c
> >> @@ -125,7 +125,6 @@ void (*pm_power_off)(void);
> >>   EXPORT_SYMBOL(pm_power_off);
> >>
> >>   void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd) = null_restart;
> >> -EXPORT_SYMBOL_GPL(arm_pm_restart);
> >
> > Unless I miss something, how is this different from registering a
> > restart notifier from a module (blocking_notifier_chain_register is
> > exported)?
> 
> A notifier can be unregistered safely, and more than one notifier call
> is supported. If there is more than one driver setting arm_pm_restart,
> the first one to unregister will clear the pointer. Using the notifier
> is cleaner and not architecture dependent. One might argue that setting
> module external function pointers from module code isn't exactly clean
> coding.

I agree.

> Anyway, this patch is not relevant for the series. If you prefer to have
> the function exported, and keep using it for arm drivers loaded as modules,
> be my guest, and I'll be more than happy drop it. I'll take your comment
> as a hint _not_ to convert existing code to use the notifier after the
> series is accepted. Cool, as I hate wasting my time.

No, it's actually the opposite ;) (and I would go further and remove
arm_pm_restart entirely for arm64).

-- 
Catalin
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