From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755189AbZJLJLY (ORCPT ); Mon, 12 Oct 2009 05:11:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754700AbZJLJLY (ORCPT ); Mon, 12 Oct 2009 05:11:24 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:60643 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754692AbZJLJLX (ORCPT ); Mon, 12 Oct 2009 05:11:23 -0400 Date: Mon, 12 Oct 2009 11:10:28 +0200 From: Ingo Molnar To: Frederic Weisbecker Cc: LKML , Peter Zijlstra , Arnaldo Carvalho de Melo , Mike Galbraith , Paul Mackerras Subject: Re: [PATCH] perf tools: Provide backward compatibility with previous perf.data version Message-ID: <20091012091028.GB24031@elte.hu> References: <1255032449-12022-1-git-send-email-fweisbec@gmail.com> <20091008202226.GE5073@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091008202226.GE5073@nowhere> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Frederic Weisbecker wrote: > On Thu, Oct 08, 2009 at 10:07:29PM +0200, Frederic Weisbecker wrote: > > We have merged the trace.info file into perf.data by adding one section > > in the perf headers. This makes it incompatible with previous version: > > the new perf tools can't read the older perf.data. > > > > To support the previous format, we check the headers size. If they > > have the same size than in the previous format, then ignore the trace > > info section that doesn't exist. > > > > Signed-off-by: Frederic Weisbecker > > Cc: Peter Zijlstra > > Cc: Arnaldo Carvalho de Melo > > Cc: Mike Galbraith > > Cc: Paul Mackerras > > --- > > tools/perf/util/header.c | 8 +++++++- > > 1 files changed, 7 insertions(+), 1 deletions(-) > > > > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c > > index 212fade..9aae360 100644 > > --- a/tools/perf/util/header.c > > +++ b/tools/perf/util/header.c > > @@ -287,10 +287,16 @@ struct perf_header *perf_header__read(int fd) > > do_read(fd, &f_header, sizeof(f_header)); > > > > if (f_header.magic != PERF_MAGIC || > > - f_header.size != sizeof(f_header) || > > > > Few notes about this. > I can send a separate fix for .32 that would just consist in the above line, > or more likely I can replace it by: > > f_header.size < sizeof(f_header) || > > and then we'll get a minimal forward compatibility from the older > tools (can be Cc'ed to stable for .31). Yep, would be nice. > Another thing. We may feel the need to add yet another sections in the > future. > > So just a suggestion: we could turn this trace_info section into a > more generic one in which we could add as much subsections as we want > in the future while always ensuring backward compatibility. That could > be managed through a versioning of this generic section. Definitely! (Since it's not upstream yet we can do it without supporting the interim version.) Ingo