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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E8C2C433EF for ; Fri, 24 Jun 2022 15:49:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231494AbiFXPtS (ORCPT ); Fri, 24 Jun 2022 11:49:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229801AbiFXPtR (ORCPT ); Fri, 24 Jun 2022 11:49:17 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD1474AE18 for ; Fri, 24 Jun 2022 08:49:16 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 5474B21A5B; Fri, 24 Jun 2022 15:49:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1656085755; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9emSbOo2BbJrk5i6dfyOK7q9UTAJdcelXAG8LisgtY4=; b=ZPz7cdpREUJm21cv/NwLjaYdQPsY7qncOcTrKGLsSEuJ/y2BOyO9fglLrI/nAuC56OeZL5 zt4HL09mo0Jsxdx/gi+1WIx3vREVjDw3jKxRaiAQeAypTA+wRLmbBxYRR86knXNabDRlph Xhz6Vvw43+eMbUwyZSOSMyawhz9/P6c= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1656085755; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9emSbOo2BbJrk5i6dfyOK7q9UTAJdcelXAG8LisgtY4=; b=1BoyoO4DAdHG2EdTBkv/cATfAOOnrZgsHDn074wvewfJZMd7g60rfkAzqh3LVLTp7aJrMK 4LSRElCpaYfpWVCA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 24B2113480; Fri, 24 Jun 2022 15:49:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id ZRj0B/vctWIeRgAAMHmgww (envelope-from ); Fri, 24 Jun 2022 15:49:15 +0000 Date: Fri, 24 Jun 2022 17:44:36 +0200 From: David Sterba To: Qu Wenruo Cc: dsterba@suse.cz, Qu Wenruo , Nikolay Borisov , linux-btrfs@vger.kernel.org Subject: Re: [PATCH 1/2] btrfs: remove MIXED_BACKREF sysfs file Message-ID: <20220624154436.GW20633@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , Nikolay Borisov , linux-btrfs@vger.kernel.org References: <20220624080123.1521917-1-nborisov@suse.com> <20220624080123.1521917-2-nborisov@suse.com> <21f7eb10-09d7-826c-48c3-ded892984d50@gmx.com> <3e01475c-8296-4cf1-14cd-5774d780b6e2@suse.com> <27f72ec4-a365-20ba-03f1-8d603a66e011@gmx.com> <20220624134706.GV20633@twin.jikos.cz> <75cb4383-72e3-58d6-ca23-fbfa9be65617@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <75cb4383-72e3-58d6-ca23-fbfa9be65617@suse.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Jun 24, 2022 at 10:02:43PM +0800, Qu Wenruo wrote: > > > On 2022/6/24 21:47, David Sterba wrote: > > On Fri, Jun 24, 2022 at 07:46:12PM +0800, Qu Wenruo wrote: > >> On 2022/6/24 19:32, Nikolay Borisov wrote: > >>> On 24.06.22 г. 11:13 ч., Qu Wenruo wrote: > >>>> > >>>> I don't think that's the correct way to go. > >>>> > >>>> In fact, I think sysfs should have everything, no matter how long > >>>> supported it is. > >>> > >>> I disagree, for things which are considered stand alone features - yes. > >>> Like free space tree 2, but for something like backrefs, heck I think > >>> we've even removed code which predates mixed backrefs so I'm not > >>> entirely use the filesystem can function with that feature turned off, > >>> actually it's not possible to create a non-mixedbackref file system > >>> since this behavior is hard-coded in btrfs-progs. Also the commit for > >>> the backrefs states: > >>> > >>> > >>> This commit introduces a new kind of back reference for btrfs metadata. > >>> Once a filesystem has been mounted with this commit, IT WILL NO LONGER > >>> BE MOUNTABLE BY OLDER KERNELS. > >> > >> That means we're hiding incompat features from the user. > >> > >> Even if it's not tunable and should always be enabled, we still need to > >> add that. > > > > I think the mixed_backref is an exception because it's been part of the > > default format for so long that we don't even remember there was > > something else. For users it does not mean anything today, moreover it > > could be confused with mixed block groups. > > Then after some time, there will be some "smart" users find that we have > one incompat bit without any explanation. Removed functionality is documented, the sysfs feature files are in manual pages and we can add a notice in which version it was removed.