linux-kernel - Re: [PATCH 31/34] move virtrng

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Message-ID: <20091001174116.GA27288@pengutronix.de>
Date:	Thu, 1 Oct 2009 19:41:16 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 31/34] move virtrng_remove to .devexit.text

Hello Michael,

> > But note it's not an error in general to use a .text function as remove
> > callback.  E.g. take drivers/gpio/twl4030-gpio.c.  gpio_twl4030_remove
> > is used in gpio_twl4030_probe which is defined using __devinit.  So
> > using __devexit for gpio_twl4030_remove is wrong.  (So there is a bug,
> > as gpio_twl4030_remove uses __devexit.)  I didn't try, but as far as I
> > understand this will result in a compile error if the driver is built-in
> > with HOTPLUG=n.
> 
> Wait a second.
> As far as I understand, __devexit makes it possible to remove code if
> hotplug is off.
right.
 
> At least for static functions, it's enough to mark their only use
> as _devexit_p, and compiler will remove the text as it's unused.
> 
> Isn't that right?
hmm, I don't know.  I'll try, one moment.  OK, you're right.  The
function is discarded with a compiler warning.
 
> If so, what, again, was the motivation for the patches that added
> __devexit to functions that were already used with __devexit_p?
I thought it saves some memory, but as it looks now it only fixes a
compiler warning.

Note there are two types of errors fixed in this series.  One is:

	-static int func(void arg)
	+static int __devexit func(void arg)

if the only usage of func() is wraped by __devexit_p.  This is (as
seen above) not that critical, there is only a warning fixed.

The other type results in a build failure:

	-remove = __devexit_p(another_func),
	+remove = __exit_p(another_func),

with another_func being defined using __exit.  In the case 
defined(MODULE) && defined(CONFIG_HOTPLUG) another_func is discarded,
but __devexit_p(another_func) evaluates to another_func and thus the
module doesn't link.

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |
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