From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756070AbZJASTT (ORCPT ); Thu, 1 Oct 2009 14:19:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755927AbZJASTS (ORCPT ); Thu, 1 Oct 2009 14:19:18 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:44775 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755799AbZJASTS (ORCPT ); Thu, 1 Oct 2009 14:19:18 -0400 Date: Thu, 1 Oct 2009 20:19:20 +0200 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: "Michael S. Tsirkin" Cc: Christian Borntraeger , linux-kernel@vger.kernel.org, Sam Ravnborg , Andrew Morton , Rusty Russell Subject: Re: [PATCH 31/34] move virtrng_remove to .devexit.text Message-ID: <20091001181920.GC27288@pengutronix.de> References: <20091001082607.GA2181@pengutronix.de> <1254385718-14254-31-git-send-email-u.kleine-koenig@pengutronix.de> <200910011044.48293.borntraeger@de.ibm.com> <20091001091218.GE5718@redhat.com> <20091001093106.GA6386@pengutronix.de> <20091001094518.GI5718@redhat.com> <20091001101727.GC6386@pengutronix.de> <20091001123213.GL5718@redhat.com> <20091001174116.GA27288@pengutronix.de> <20091001180500.GA11984@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20091001180500.GA11984@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:215:17ff:fe12:23b0 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Michael, On Thu, Oct 01, 2009 at 08:05:00PM +0200, Michael S. Tsirkin wrote: > On Thu, Oct 01, 2009 at 07:41:16PM +0200, Uwe Kleine-König wrote: > > 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. > > We can redefine __devexit_p(x) to something like > #define __devexit_p(x) ((typeof(x) *)NULL) > and this will shut down the warning without need to fix the code. Mmmmh, don't know. A definitive advantage is that there is only a single point in the code that defines if a function is discarded or not. Nothing that needs to be consistent. For me it feels somehow wrong anyhow, but that might be only because I'm used to the current model. > > 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. > > Yes, calling __exit function from non- __exit is always a bug. > I think there's a make flag to warn about this, not sure why it's > not the default. I think it was disabled because there were too many warnings :-) Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |