From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753234AbXLDLls (ORCPT ); Tue, 4 Dec 2007 06:41:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752542AbXLDLlk (ORCPT ); Tue, 4 Dec 2007 06:41:40 -0500 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:60454 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752416AbXLDLlj (ORCPT ); Tue, 4 Dec 2007 06:41:39 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Andrew Morton 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 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> Date: Tue, 04 Dec 2007 04:40:26 -0700 In-Reply-To: <20071204014549.8fe47f7f.akpm@linux-foundation.org> (Andrew Morton's message of "Tue, 4 Dec 2007 01:45:49 -0800") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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