From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753033AbXLDLtT (ORCPT ); Tue, 4 Dec 2007 06:49:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752313AbXLDLtL (ORCPT ); Tue, 4 Dec 2007 06:49:11 -0500 Received: from smtp2.linux-foundation.org ([207.189.120.14]:45572 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751356AbXLDLtJ (ORCPT ); Tue, 4 Dec 2007 06:49:09 -0500 Date: Tue, 4 Dec 2007 03:48:36 -0800 From: Andrew Morton To: ebiederm@xmission.com (Eric W. Biederman) Cc: Pavel Emelyanov , linux-kernel@vger.kernel.org, devel@openvz.org Subject: Re: [PATCH 1/7][QUOTA] Move sysctl management code under ifdef CONFIG_SYSCTL Message-Id: <20071204034836.47211436.akpm@linux-foundation.org> In-Reply-To: References: <475008F5.3000506@openvz.org> <475009FA.20409@openvz.org> <20071203133844.40804dab.akpm@linux-foundation.org> <475516B6.5000504@openvz.org> <20071204012301.4349bbd0.akpm@linux-foundation.org> <47551E79.6080802@openvz.org> <20071204014549.8fe47f7f.akpm@linux-foundation.org> X-Mailer: Sylpheed 2.4.1 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 04 Dec 2007 04:40:26 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote: > Andrew Morton writes: > > > On Tue, 04 Dec 2007 12:31:37 +0300 Pavel Emelyanov wrote: > > > >> Andrew Morton wrote: > >> > On Tue, 04 Dec 2007 11:58:30 +0300 Pavel Emelyanov wrote: > >> > > >> >>>> +#ifdef CONFIG_SYSCTL > >> >>>> register_sysctl_table(sys_table); > >> >>>> +#endif > >> >>>> > >> >>>> dquot_cachep = kmem_cache_create("dquot", > >> >>>> sizeof(struct dquot), sizeof(unsigned long) * 4, > >> >>> We should avoid the ifdefs around the register_sysctl_table() call. > >> >>> > >> >>> At present the !CONFIG_SYSCTL implementation of register_sysctl_table() is > >> >>> a non-inlined NULL-returning stub. All we have to do is to inline that > > stub > >> >>> then these ifdefs can go away. > >> >> What if some code checks for the return value to be not-NULL? In case > >> >> CONFIG_SYSCTL=n this code will always think, that the registration failed. > >> > > >> > The stub function should return success? > >> > >> Well, I think yes. If some functionality is turned off, then the > >> caller should think that everything is going fine (or he should > >> explicitly removes the call to it with some other ifdef). > >> > >> At least this is true for stubs that return the error code, not > >> the pointer. E.g. copy_semundo() always returns success if SYSVIPC > >> is off, or namespaces cloning routines act in a similar way. > >> > >> Thus I though, that routines, that return pointers should better > >> report that everything is OK (somehow) to reduce the number of > >> "helpers" in the outer code. No? > >> > > > > Dunno. Returning NULL should be OK. If anyone is dereferenceing that > > pointer with CONFIG_SYSCTL=n then they might need some attention? > > We do have some current code in the network stack that fails miserably > when register_sysctl_table returns NULL, and there are explicit > checks for that. So that code would be failing today with CONFIG_SYSCTL=n? Unless the failing code is itself under #ifdef CONFIG_SYSCTL, in which case we don't need to change anything? > Grr. > > I had forgotten about that. > > I expect the right answer is to simply have code ignore the fact > that register_sysctl_xxxx returns NULL, and not error on it. > > The alternative is to get fancy and have everyone check the > return code and make the return type an IS_ERR thing. That seems > a lot more trouble then it is worth. > > We can probably define it as register_sysctl_xxxx always returns > a token that must be passed to unregister_sysctl, and no errors > will be reported except to dmesg. That at sounds simple sane > and supportable from where we are now. > > Eric > >