From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB699C433DB for ; Mon, 15 Mar 2021 23:21:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6814064DE5 for ; Mon, 15 Mar 2021 23:21:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231594AbhCOXUf (ORCPT ); Mon, 15 Mar 2021 19:20:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:43822 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231245AbhCOXUZ (ORCPT ); Mon, 15 Mar 2021 19:20:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 07CE9AC1D; Mon, 15 Mar 2021 23:20:24 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id B0DFEDA6E2; Tue, 16 Mar 2021 00:18:22 +0100 (CET) Date: Tue, 16 Mar 2021 00:18:22 +0100 From: David Sterba To: Pierre Labastie Cc: dsterba@suse.cz, linux-btrfs@vger.kernel.org Subject: Re: [PATCH v2] btrfs-progs: build system: Fix the test for EXT4_EPOCH_MASK Message-ID: <20210315231822.GC7604@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Pierre Labastie , linux-btrfs@vger.kernel.org References: <20210314184913.5689-1-pierre.labastie@neuf.fr> <20210315145324.GU7604@twin.jikos.cz> <26cdac5a09c1f51f04bdea9ca59f1be9fdbb5406.camel@neuf.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <26cdac5a09c1f51f04bdea9ca59f1be9fdbb5406.camel@neuf.fr> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Mar 15, 2021 at 11:19:47PM +0100, Pierre Labastie wrote: > On Mon, 2021-03-15 at 15:53 +0100, David Sterba wrote: > > On Sun, Mar 14, 2021 at 07:49:13PM +0100, Pierre Labastie wrote: > > > +AX_CHECK_DEFINE([ext2fs/ext2_fs.h], [EXT4_EPOCH_MASK], > > > +                [AC_DEFINE([HAVE_EXT4_EPOCH_MASK_DEFINE], [1], > > > +                   [Define to 1 if e2fsprogs defines EXT4_EPOCH_MASK])], > > > +               [AC_MSG_WARN([no definition of EXT4_EPOCH_MASK found, > > > probably old e2fsprogs, will use own definition, no 64bit time precision of > > > converted images])]) > > > > Inlining the AC_DEFINE to the check will skip defining the macro in case > > the EXT4_EPOCH_MASK does not exist and then the C #if won't work. > > > >         HAVE_EXT4_EPOCH_MASK_DEFINE=0 > >         AX_CHECK_DEFINE(... > >                 HAVE_EXT4_EPOCH_MASK_DEFINE=1,...) > > > >         if x"$HAVE_EXT4_EPOCH_MASK_DEFINE"; then > >                 AC_DEFINE([HAVE_EXT4_EPOCH_MASK_DEFINE], [1]) > >         else > >                 AC_DEFINE([HAVE_EXT4_EPOCH_MASK_DEFINE], [0]) > >         fi > > Since autoheader is used, and autoheader uses AC_DEFINE macros to generate > config.h.in, there is a risk that having two AC_DEFINE macros for the same > identifier generates a conflict. I've not been able to find what it does in > that case in the autoconf doc. > > OTOH, an undefined identifier is replaced by a zero when expanding a #if in the > C preprocessor (this is in all the norms I have access to: C89 and C99), that > is: > > #if UNDEFINED_IDENTIFIER > is equivalent to > #if 0 > > Except if a compiler does not respect the norm, what I have proposed works (I > have only tested with gcc, and it does what it is supposed to do). I'll change it back to what you did as it sounds safer. The "#if undefined" works for all compilers we currently care about (gcc, clang) and would avoid potential problems with autoheader. > > This should work, maybe it's not the shortest way to write that but I > > can't find anything better. > > Now, I've tested your version, and it works too. So, up to you... I take yours, thanks. Feel free to send a fix to AC_DEFINE of HAVE_OWN_FIEMAP_EXTENT_SHARED_DEFINE that does the double definition. There were no problems reported so far but for consistency it would be better to unify them.