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=-0.5 required=3.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 25E79C32788 for ; Thu, 11 Oct 2018 13:13:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DEB3820841 for ; Thu, 11 Oct 2018 13:13:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DEB3820841 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gmx.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727835AbeJKUk2 (ORCPT ); Thu, 11 Oct 2018 16:40:28 -0400 Received: from mout.gmx.net ([212.227.17.21]:37191 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726126AbeJKUk1 (ORCPT ); Thu, 11 Oct 2018 16:40:27 -0400 Received: from [0.0.0.0] ([210.140.77.29]) by mail.gmx.com (mrgmx102 [212.227.17.174]) with ESMTPSA (Nemesis) id 0MM0bQ-1g2tfx42DE-007ja0; Thu, 11 Oct 2018 15:13:15 +0200 Received: from [0.0.0.0] ([210.140.77.29]) by mail.gmx.com (mrgmx102 [212.227.17.174]) with ESMTPSA (Nemesis) id 0MM0bQ-1g2tfx42DE-007ja0; Thu, 11 Oct 2018 15:13:15 +0200 Subject: Re: [PATCH 1/2] btrfs: Populate btrfs_super_block::log_root_transid To: Nikolay Borisov , dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org References: <20181004054950.11651-1-wqu@suse.com> <20181004054950.11651-2-wqu@suse.com> <20181011123151.GP29418@twin.jikos.cz> <2971327e-aa24-534c-cbfb-3ba9f399c6f2@suse.com> From: Qu Wenruo Openpgp: preference=signencrypt Autocrypt: addr=quwenruo.btrfs@gmx.com; prefer-encrypt=mutual; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWCnQUJCWYC bgAKCRDCPZHzoSX+qAR8B/94VAsSNygx1C6dhb1u1Wp1Jr/lfO7QIOK/nf1PF0VpYjTQ2au8 ihf/RApTna31sVjBx3jzlmpy+lDoPdXwbI3Czx1PwDbdhAAjdRbvBmwM6cUWyqD+zjVm4RTG rFTPi3E7828YJ71Vpda2qghOYdnC45xCcjmHh8FwReLzsV2A6FtXsvd87bq6Iw2axOHVUax2 FGSbardMsHrya1dC2jF2R6n0uxaIc1bWGweYsq0LXvLcvjWH+zDgzYCUB0cfb+6Ib/ipSCYp 3i8BevMsTs62MOBmKz7til6Zdz0kkqDdSNOq8LgWGLOwUTqBh71+lqN2XBpTDu1eLZaNbxSI ilaVzsBNBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAHCwHwEGAEIACYWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWBrwIbDAUJA8JnAAAK CRDCPZHzoSX+qA3xB/4zS8zYh3Cbm3FllKz7+RKBw/ETBibFSKedQkbJzRlZhBc+XRwF61mi f0SXSdqKMbM1a98fEg8H5kV6GTo62BzvynVrf/FyT+zWbIVEuuZttMk2gWLIvbmWNyrQnzPl mnjK4AEvZGIt1pk+3+N/CMEfAZH5Aqnp0PaoytRZ/1vtMXNgMxlfNnb96giC3KMR6U0E+siA 4V7biIoyNoaN33t8m5FwEwd2FQDG9dAXWhG13zcm9gnk63BN3wyCQR+X5+jsfBaS4dvNzvQv h8Uq/YGjCoV1ofKYh3WKMY8avjq25nlrhzD/Nto9jHp8niwr21K//pXVA81R2qaXqGbql+zo Message-ID: <5edcb70a-a9c7-dc06-7a09-fd287e315612@gmx.com> Date: Thu, 11 Oct 2018 21:13:08 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <2971327e-aa24-534c-cbfb-3ba9f399c6f2@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Provags-ID: V03:K1:FYRjQrccSA92+lhz0YU/SwCcaYMT7BRdpVVlDaLeRCxeVGR2Yo5 Wt5YIprHcPsXS3MOn12oZIoudCelkcVt2xdG9ZFJyBrI6FUDafuT2zHrxRy52G3AaPd2PeI enOXUl6Q2IaVyJwVhT9QhgaGnq1Lksc4LDqfUyobL9iszZvT+xu24giW0OjySjqDCVujkaP 2DAXnIPrwREaq/GNAjt7g== X-UI-Out-Filterresults: notjunk:1;V01:K0:hBxQZmwRlrA=:xZdH9VbpL82H32xAHslhbr ME/UOPRIeVGxyGKfE+1kpiRHQMhsTitAt5EXlgkft5dUjeBgi1cIxwMbj/MX2tKXnE+tV1enI /P8huUJh9ZZOhT2ucqpwYd3TA+UV4gssadA6D91G8kHzhYI9qQhytjKDd3ZdvBe3GLenQETqH M2GebIIC0Zmvrbyf418JFrwY2cSeqjMK11dFoZnzgPJRJW+IDtAfBphvFKP8W6Z1ue3RV5+E+ v3I4Uj7LPt16wCk01EWHEqFuOZAZl81V9DBSaj70ODELB4NooSV7ZCNK1r5vZhH8ufnZUgzLx miJcjvR3IdKbSpuM+HWCqbnQE4v5KwzwYPayus13XB0DZhpDW7wQOlCmRTrhVr8vaLE06iGFd trfrgeg7Pt9TBe12o46t6TAJKhwauzxE4+GTqncJGTFa2tk3Ex7euY8gkC+35ZohlI70XtA92 z/9xWs3xF9MfKdKhLQszOFO9duMVQZckTf2HGPJsrjL2yyuxEETnapu00ex2GF25GXuX3Lwcz 64agjakqhPKxlZ9Uz7DHi9tG+/U7R5I0pZqRlfqm7pOYqAx/LpqF6fsHBAOjl/DjzuXSCeOp8 EFP6FX2wQc+Q3zRU5LHmshE3oafU44j2GGE4TF99Ke3TnXCw0DUbcb8d6NwWn0JMpRZ2ej/F/ BnOHa2PY9Bln6MMEtOCgUuwxaBXbls78mtY9JPHgj3+IC7J9/BlkuY+dRaiCtXZM/T6yc19Kw dvXSxxg6tf9Kle5g9IQ66mgjkpwH+bs3p/9cA4nO7FF2LgHOJ2eT7EXaawCGRa/hO5Y75ByLw ZXuFJ5AAQVx1nsTySog6ebqP9fUBWquy92I97zyXCObKIIcAQE= Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2018/10/11 下午9:11, Nikolay Borisov wrote: > > > On 11.10.2018 15:45, Qu Wenruo wrote: >> >> >> On 2018/10/11 下午8:31, David Sterba wrote: >>> On Thu, Oct 04, 2018 at 01:49:49PM +0800, Qu Wenruo wrote: >>>> We have btrfs_super_block::log_root_transid to record the transid of log >>>> tree root. >>>> >>>> However it's never populated and it's always 0, just as the following >>>> dump-super: >>>> log_root 30572544 >>>> log_root_transid 0 >>>> log_root_level 0 >>>> >>>> This patch will populate it with log tree root correctly, so the result >>>> will be: >>>> log_root 30572544 >>>> log_root_transid 6 >>>> log_root_level 0 >>>> >>>> This won't affect current kernel behavior or btrfs check result as we >>>> already expect log tree root generation always to be super block >>>> genration + 1. >>>> >>>> But it could be later used to detect log tree corruption early. >>> >>> The backward compatibility seems to be ok in general, I found one >>> scenario where the check will fail: >>> >>> * mount with unpatched kernel, log_root_transid = 0 >>> * mount with patched kernel, log_root_transid 100, generation 101 >>> * mount with unpatched kernel, log_root_transid 100 (unchanged), generation 201 >>> * mount with patched kernel -> check fails >> >> Indeed, this is a problem I missed. >> >> It provides the old principle, if we're going to change how kernel >> use/interprete a on-disk memeber, we have to introduce a new >> incompatible flag. >> >> Please just drop the series of patch. > > Since this member really doesn't have any purpose now I think the > prudent thing to do is to rename it to "reserved1" or "padding" or > whatever but basically signal that it's no longer in used. In the future > when a new incompaat bit will be required for some feature it can be > re-used. Makes sense. I'll craft a patch for that. Thanks, Qu > >> >> Thanks, >> Qu >>> >>> So the problem is when log_root_transid is not 0 and changes out of sync >>> with the generation. The above sequence of kernels can simply happen >>> when switching between old stable and current releases. >>> >>