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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 88D4EC433ED for ; Thu, 29 Apr 2021 13:16:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3848161158 for ; Thu, 29 Apr 2021 13:16:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233602AbhD2NR3 (ORCPT ); Thu, 29 Apr 2021 09:17:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:36416 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231343AbhD2NR3 (ORCPT ); Thu, 29 Apr 2021 09:17:29 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9982C61158; Thu, 29 Apr 2021 13:16:42 +0000 (UTC) Date: Thu, 29 Apr 2021 09:16:40 -0400 From: Steven Rostedt To: Tzvetomir Stoyanov Cc: Linux Trace Devel Subject: Re: [PATCH 1/6] trace-cmd library: Bump the trace file version to 7 Message-ID: <20210429091640.27dde3d8@gandalf.local.home> In-Reply-To: References: <20210422071718.483383-1-tz.stoyanov@gmail.com> <20210422071718.483383-2-tz.stoyanov@gmail.com> <20210428211920.001a66c8@oasis.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On Thu, 29 Apr 2021 06:43:54 +0300 Tzvetomir Stoyanov wrote: > On Thu, Apr 29, 2021 at 4:19 AM Steven Rostedt wrote: > > > > On Thu, 22 Apr 2021 10:17:13 +0300 > > "Tzvetomir Stoyanov (VMware)" wrote: > > > > > Adding a compression of the trace.dat file will change its structure. > > > These changes are not backward compatible, the old trace-cmd binaries > > > will not be able to read compressed trace files. Bumping the version to > > > 7 will prevent old trace-cmd to read such files. > > > > But this series doesn't add anything to the file that breaks the > > version. The version should be updated with the patch that breaks the > > backward compatibility. of the file, not before. > > > I need the new version before the compression changes, because there > is logic which relies on the new version. There is a check whether to > read / write compression data based on the new file version. I was > wondering if to put all changes into a single patchset, version + > compression. Decided to split in two, although there is no sense to > bump the version without adding a compression. The file should stay at version 6 unless it has something that old trace-cmd can not read. Right now, with this patch, if I record a trace.dat file, and I port the version check to older trace-cmd, it will think it can not read this file, even though there's nothing in this file. In fact, it should write version 6 until it writes something that is not supported by version 6. It will still need to be able to write version 6 files. In fact that's one of the requirements here. That we allow trace-cmd to create older versions if it does not use the features of the the new version. -- Steve