From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755194AbZDPDJ0 (ORCPT ); Wed, 15 Apr 2009 23:09:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751830AbZDPDJR (ORCPT ); Wed, 15 Apr 2009 23:09:17 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:37018 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbZDPDJR (ORCPT ); Wed, 15 Apr 2009 23:09:17 -0400 Date: Wed, 15 Apr 2009 23:09:14 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Jeremy Fitzhardinge cc: Mathieu Desnoyers , Ingo Molnar , Linux Kernel Mailing List Subject: Re: Problem with CREATE_TRACE_POINTS and recursion safety In-Reply-To: <49E69CED.9050706@goop.org> Message-ID: References: <49E67D1D.8020704@goop.org> <49E6847B.9000003@goop.org> <20090416022305.GA22378@Krystal> <49E69CED.9050706@goop.org> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) 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 On Wed, 15 Apr 2009, Jeremy Fitzhardinge wrote: > Mathieu Desnoyers wrote: > > Jeremy brings up an interesting point. Given that we might eventually > > include a few tracepoint header files in a given C file, but with the > > intent of only "creating" the tracepoint callbacks for few of these, the > > global "CREATE_TRACE_POINTS" flag makes little sense and seems like it > > will easily lead to link-time errors. > > > > Yes, that's what I'm seeing. > > > Maybe we could consider requiring something like the following solution : > > > > In the .c file : > > > > #define CREATE_TRACE_POINTS > > #include > > #undef CREATE_TRACE_POINTS > > > > #include > > > > Where subsysa has its trace points callbacks created, but subsysb > > doesn't. This seems half-way understandable, at least. > > But what if trace/subsysa.h includes some other headers to define some types > it needs, which in turn ends up incidentally including trace/subsysc.h (either > directly, or indirectly via any number of other headers? Then it will end up > instantiating tracepoints for subsysa and subsysc. The only way to avoid it > would be to impose an absolutely strict separation of type/constant definition > headers from function/tracepoint ones. I hate to do this because it adds some more work to the developer adding a new trace point header, but we could just remove the CREATE_TRACE_POINTS and do in the trace/events/*.h headers: #ifdef CREATE_FOO_TRACE_POINTS #include #endif in all tracepoint headers. I originally had it this way with just the CREATE_TRACE_POINTS, but Christoph Hellwig and Mathieu both suggested putting that into define_trace.h. It seems so much cleaner to keep it in define_trace.h, but if it is causing too many headaches, it may not be worth it :-/ -- Steve