Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752593AbZD2Em1 (ORCPT ); Wed, 29 Apr 2009 00:42:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751294AbZD2EmR (ORCPT ); Wed, 29 Apr 2009 00:42:17 -0400 Received: from a-sasl-fastnet.sasl.smtp.pobox.com ([207.106.133.19]:36018 "EHLO sasl.smtp.pobox.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750955AbZD2EmQ (ORCPT ); Wed, 29 Apr 2009 00:42:16 -0400 To: Wu Fengguang Cc: Andrew Morton , "linux-kernel\@vger.kernel.org" , "kosaki.motohiro\@jp.fujitsu.com" , "andi\@firstfloor.org" , "mpm\@selenic.com" , "adobriyan\@gmail.com" , "linux-mm\@kvack.org" , Stephen Rothwell , Chandra Seetharaman , Olof Johansson , Helge Deller , linuxppc-dev@ozlabs.org Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags References: <20090428010907.912554629@intel.com> <20090428014920.769723618@intel.com> <20090428143244.4e424d36.akpm@linux-foundation.org> <20090429023842.GA10266@localhost> From: Nathan Lynch Date: Tue, 28 Apr 2009 23:41:52 -0500 In-Reply-To: <20090429023842.GA10266@localhost> (Wu Fengguang's message of "Wed\, 29 Apr 2009 10\:38\:42 +0800") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Pobox-Relay-ID: 1CFC0230-3478-11DE-BAA0-CABC03BA4B0C-04752483!a-sasl-fastnet.pobox.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6136 Lines: 153 Wu Fengguang writes: > On Wed, Apr 29, 2009 at 05:32:44AM +0800, Andrew Morton wrote: >> On Tue, 28 Apr 2009 09:09:12 +0800 >> Wu Fengguang wrote: >> >> > +/* >> > + * Kernel flags are exported faithfully to Linus and his fellow hackers. >> > + * Otherwise some details are masked to avoid confusing the end user: >> > + * - some kernel flags are completely invisible >> > + * - some kernel flags are conditionally invisible on their odd usages >> > + */ >> > +#ifdef CONFIG_DEBUG_KERNEL >> > +static inline int genuine_linus(void) { return 1; } >> >> Although he's a fine chap, the use of the "_linus" tag isn't terribly >> clear (to me). I think what you're saying here is that this enables >> kernel-developer-only features, yes? > > Yes. > >> If so, perhaps we could come up with an identifier which expresses that >> more clearly. >> >> But I'd expect that everyone and all distros enable CONFIG_DEBUG_KERNEL >> for _some_ reason, so what's the point? At the least, it has not always been so... > > Good point! I can confirm my debian has CONFIG_DEBUG_KERNEL=Y! I can confirm mine does not. etch-i386:~# uname -a Linux etch-i386 2.6.18-6-686 #1 SMP Fri Dec 12 16:48:28 UTC 2008 i686 GNU/Linux etch-i386:~# grep DEBUG_KERNEL /boot/config-2.6.18-6-686 # CONFIG_DEBUG_KERNEL is not set For what that's worth. >> It is preferable that we always implement the same interface for all >> Kconfig settings. If this exposes information which is confusing or >> not useful to end-users then so be it - we should be able to cover that >> in supporting documentation. > > My original patch takes that straightforward manner - and I still like it. > I would be very glad to move the filtering code from kernel to user space. > > The use of more obscure flags could be discouraged by _not_ documenting > them. A really curious user is encouraged to refer to the code for the > exact meaning (and perhaps become a kernel developer ;-) > >> Also, as mentioned in the other email, it would be good if we were to >> publish a little userspace app which people can use to access this raw >> data. We could give that application an `--i-am-a-kernel-developer' >> option! > > OK. I'll include page-types.c in the next take. > >> > +#else >> > +static inline int genuine_linus(void) { return 0; } >> > +#endif >> >> This isn't an appropriate use of CONFIG_DEBUG_KERNEL. >> >> DEBUG_KERNEL is a Kconfig-only construct which is use to enable _other_ >> debugging features. The way you've used it here, if the person who is >> configuring the kernel wants to enable any other completely-unrelated >> debug feature, they have to enable DEBUG_KERNEL first. But when they >> do that, they unexpectedly alter the behaviour of pagemap! >> >> There are two other places where CONFIG_DEBUG_KERNEL affects code >> generation in .c files: arch/parisc/mm/init.c and >> arch/powerpc/kernel/sysfs.c. These are both wrong, and need slapping ;) > > (add cc to related maintainers) I assume I was cc'd because I've changed arch/powerpc/kernel/sysfs.c a couple of times in the last year, but I can't claim to maintain that code. I'm pretty sure I haven't touched the code in question in this discussion. I've cc'd linuxppc-dev. > CONFIG_DEBUG_KERNEL being enabled in distro kernels effectively means > > #ifdef CONFIG_DEBUG_KERNEL == #if 1 > > as the following patch demos. Now it becomes obviously silly. Sure, #if 1 is usually silly. But if the point is that DEBUG_KERNEL is not supposed to directly affect code generation, then I see two options for powerpc: - remove the #ifdef CONFIG_DEBUG_KERNEL guards from arch/powerpc/kernel/sysfs.c, unconditionally enabling the hid/ima sysfs attributes, or - define a new config symbol which governs whether those attributes are enabled, and make it depend on DEBUG_KERNEL > --- a/arch/powerpc/kernel/sysfs.c > +++ b/arch/powerpc/kernel/sysfs.c > @@ -212,19 +212,19 @@ static SYSDEV_ATTR(purr, 0600, show_purr, store_purr); > #endif /* CONFIG_PPC64 */ > > #ifdef HAS_PPC_PMC_PA6T > SYSFS_PMCSETUP(pa6t_pmc0, SPRN_PA6T_PMC0); > SYSFS_PMCSETUP(pa6t_pmc1, SPRN_PA6T_PMC1); > SYSFS_PMCSETUP(pa6t_pmc2, SPRN_PA6T_PMC2); > SYSFS_PMCSETUP(pa6t_pmc3, SPRN_PA6T_PMC3); > SYSFS_PMCSETUP(pa6t_pmc4, SPRN_PA6T_PMC4); > SYSFS_PMCSETUP(pa6t_pmc5, SPRN_PA6T_PMC5); > -#ifdef CONFIG_DEBUG_KERNEL > +#if 1 > SYSFS_PMCSETUP(hid0, SPRN_HID0); > SYSFS_PMCSETUP(hid1, SPRN_HID1); > SYSFS_PMCSETUP(hid4, SPRN_HID4); > SYSFS_PMCSETUP(hid5, SPRN_HID5); > SYSFS_PMCSETUP(ima0, SPRN_PA6T_IMA0); > SYSFS_PMCSETUP(ima1, SPRN_PA6T_IMA1); > SYSFS_PMCSETUP(ima2, SPRN_PA6T_IMA2); > SYSFS_PMCSETUP(ima3, SPRN_PA6T_IMA3); > SYSFS_PMCSETUP(ima4, SPRN_PA6T_IMA4); > @@ -282,19 +282,19 @@ static struct sysdev_attribute classic_pmc_attrs[] = { > static struct sysdev_attribute pa6t_attrs[] = { > _SYSDEV_ATTR(mmcr0, 0600, show_mmcr0, store_mmcr0), > _SYSDEV_ATTR(mmcr1, 0600, show_mmcr1, store_mmcr1), > _SYSDEV_ATTR(pmc0, 0600, show_pa6t_pmc0, store_pa6t_pmc0), > _SYSDEV_ATTR(pmc1, 0600, show_pa6t_pmc1, store_pa6t_pmc1), > _SYSDEV_ATTR(pmc2, 0600, show_pa6t_pmc2, store_pa6t_pmc2), > _SYSDEV_ATTR(pmc3, 0600, show_pa6t_pmc3, store_pa6t_pmc3), > _SYSDEV_ATTR(pmc4, 0600, show_pa6t_pmc4, store_pa6t_pmc4), > _SYSDEV_ATTR(pmc5, 0600, show_pa6t_pmc5, store_pa6t_pmc5), > -#ifdef CONFIG_DEBUG_KERNEL > +#if 1 > _SYSDEV_ATTR(hid0, 0600, show_hid0, store_hid0), > _SYSDEV_ATTR(hid1, 0600, show_hid1, store_hid1), > _SYSDEV_ATTR(hid4, 0600, show_hid4, store_hid4), > _SYSDEV_ATTR(hid5, 0600, show_hid5, store_hid5), > _SYSDEV_ATTR(ima0, 0600, show_ima0, store_ima0), > _SYSDEV_ATTR(ima1, 0600, show_ima1, store_ima1), > _SYSDEV_ATTR(ima2, 0600, show_ima2, store_ima2), > _SYSDEV_ATTR(ima3, 0600, show_ima3, store_ima3), > _SYSDEV_ATTR(ima4, 0600, show_ima4, store_ima4), > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/