Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755246AbbDUMKM (ORCPT ); Tue, 21 Apr 2015 08:10:12 -0400 Received: from mail03v-smtp01.fnal.gov ([131.225.199.28]:5650 "EHLO ex-smtp.fnal.gov" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753828AbbDUMKK (ORCPT ); Tue, 21 Apr 2015 08:10:10 -0400 X-Greylist: delayed 323 seconds by postgrey-1.27 at vger.kernel.org; Tue, 21 Apr 2015 08:10:10 EDT Message-ID: <55363CDC.4000305@fnal.gov> Date: Tue, 21 Apr 2015 07:04:44 -0500 From: Ron Rechenmacher Reply-To: User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Christoph Hellwig CC: , Steven Rostedt Subject: Re: [PATCH] tracing: Export key trace event symbols References: <553571C3.1060505@fnal.gov> <20150421061034.GA9253@infradead.org> In-Reply-To: <20150421061034.GA9253@infradead.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [99.141.209.99] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1883 Lines: 40 Christoph Hellwig wrote on 04/21/15 01:10: > > Which (in-tree) module fails with this? I don't think anyone should > actually register a symbol. > I see you (Christoph Hellwig) have asked this question in a similar context (see https://patches.linaro.org/28821/). This question does not seem to make sense because: 1) the external module is not registering a _symbol_ but more precisely a tracepoint _function_ as the whole tracepoint system allows for _multiple_ functions to be called for each tracepoint declared in the kernel. 2) It's not the point that an in-tree module would fail. Again, the tracepoint system allows for _multiple_functions_ to be defined/registered for each tracepoint and _in_the_earlier_kernels_(i.e. 3.10.x and many others),_external_modules_could_ _register_ one or more _additional_functions_ to be called. IF you're specifically saying that external modules should not register additional tracepoint functions, my question would simply be: why do you think this? To give you an example of the usefulness of continuing to allow this (continuation from earlier kernels): the kernel scheduling has a tracepoint defined; of course a critical operation for any kernel. I use to be able to insert a module which would collect my own statistics on when and what switching was going on on what CPU cores. I can think of many other potential reasons that this would be useful for external modules. To think that tracepoints would only be useful for in-tree development is, perhaps, (not meaning to offend) short sighted. -- Ron Rechenmacher Engineer Fermi National Accelerator Laboratory Batavia, IL 60510 -- 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/