From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757954AbbCDBHo (ORCPT ); Tue, 3 Mar 2015 20:07:44 -0500 Received: from omr1.cc.vt.edu ([198.82.141.52]:47694 "EHLO omr1.cc.vt.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757705AbbCDBHn (ORCPT ); Tue, 3 Mar 2015 20:07:43 -0500 X-Mailer: exmh version 2.8.0 04/21/2012 with nmh-1.6+dev To: akpm@linux-foundation.org, linus@linux-foundation.org cc: linux-kernel@vger.kernel.org Subject: [RFC PATCH] Don't reset timestamps in include/generated if not needed From: Valdis Kletnieks Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Tue, 03 Mar 2015 20:07:36 -0500 Message-ID: <15447.1425431256@turing-police.cc.vt.edu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kbuild regenerates bounds.h and asm-offsets.h, resetting the timestamps and forcing rebuilds even if the contents haven't changed. Add a bit of shell magic to only replace the file if the contents have in fact changed, which should speed up git bisects and similar. Signed-off-by: Valdis Kletnieks --- So I was doing a git bisect, and getting towards the end, and wondering why it's taking a long time for each build, and I notice that netfilter modules are being rebuilt, even though 'git bisect visualize' doesn't show anything that should have touched netfilter. Turns out the offender is bounds.h Fully 3/4 of my modules have a dependency on bounds.h - and we touch it all the time, even if the contents haven't changed. RFC because I can't wrap my head around why this wasn't done ages ago. If I'm missing something something obvious, please apply a cluestick. :) Lightly tested - if I rm one of those two files, it gets rebuilt. If I insert some whitespace, it gets replaced. If I don't touch it, the datestamp doesn't change. --- linux-next/Kbuild.dist 2015-03-03 19:50:45.175673346 -0500 +++ linux-next/Kbuild 2015-03-03 20:03:20.107820199 -0500 @@ -15,7 +15,7 @@ quiet_cmd_offsets = GEN $@ define cmd_offsets - (set -e; \ + ( (set -e; \ echo "#ifndef $2"; \ echo "#define $2"; \ echo "/*"; \ @@ -26,7 +26,10 @@ echo ""; \ sed -ne $(sed-y) $<; \ echo ""; \ - echo "#endif" ) > $@ + echo "#endif" ) > $@.tmp; \ + if [ ! -f $@ ]; then mv $@.tmp $@; \ + elif cmp -s $@ $@.tmp ; then rm $@.tmp; \ + else mv -f $@.tmp $@; fi ) endef #####