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=-2.3 required=3.0 tests=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 16392CA9EB7 for ; Tue, 22 Oct 2019 12:23:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E749D2184C for ; Tue, 22 Oct 2019 12:23:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389049AbfJVMXi (ORCPT ); Tue, 22 Oct 2019 08:23:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:44868 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387575AbfJVMXh (ORCPT ); Tue, 22 Oct 2019 08:23:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2D965B293; Tue, 22 Oct 2019 12:23:36 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 098E5DA733; Tue, 22 Oct 2019 14:23:48 +0200 (CEST) Date: Tue, 22 Oct 2019 14:23:48 +0200 From: David Sterba To: Qu Wenruo Cc: dsterba@suse.cz, Qu WenRuo , "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH v2 0/7] btrfs-progs: Support for BG_TREE feature Message-ID: <20191022122348.GV3001@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , Qu WenRuo , "linux-btrfs@vger.kernel.org" References: <20191008044936.157873-1-wqu@suse.com> <20191014151723.GP2751@twin.jikos.cz> <1d23e48d-8908-5e1c-0c56-7b6ccaef5d27@gmx.com> <20191016111605.GB2751@twin.jikos.cz> <7c625485-1e2b-77f5-26ac-9386175e2621@suse.com> <20191018172745.GD3001@twin.jikos.cz> <03ba36bd-fa92-fdea-6069-da60fe4df159@gmx.com> <20191021154404.GP3001@twin.jikos.cz> <07b33628-2cec-7bd3-26a1-e3be2367774a@gmx.com> <7435bf0f-ffbc-6723-4383-d780522d5af8@gmx.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7435bf0f-ffbc-6723-4383-d780522d5af8@gmx.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Oct 22, 2019 at 02:30:22PM +0800, Qu Wenruo wrote: > BTW, there is one important compatibility problem related to all the BGI > related features. > > Although I'm putting the BG_TREE feature as incompatible feature, but in > theory, it should be RO compatible. It could be RO compatible yes. > As except extent/bg tree, we *should* read the fs without any problem. > > But the problem is, current btrfs mount (including btrfs-check) still > need to go through the block group item search, even for permanent RO mount. > > This get my rescue mount option patchset to be involved. > If we have such skip_bg feature earlier, we can completely afford to > make all these potential features as RO compatible. > > > Now my question is, should we put this feature still as incompatible > feature? In some way it would probably have to be incompat, either full or RO. As unknown tree items are ignored, if the rest of the filesystem provides enough information to access the data, then incompat RO sounds like the best option. And that's probably independent of how exactly the new BGI is done.