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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 9984BC4320A for ; Fri, 30 Jul 2021 06:09:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CDE060F4B for ; Fri, 30 Jul 2021 06:09:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237236AbhG3GJJ (ORCPT ); Fri, 30 Jul 2021 02:09:09 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:56552 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237163AbhG3GJI (ORCPT ); Fri, 30 Jul 2021 02:09:08 -0400 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 24EBD22129; Fri, 30 Jul 2021 06:09:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1627625343; h=from:from: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=yJ1yHepxiXGKkkLe9+dCqnP+TH4u121Dr/zgR8/UQ4o=; b=llbq3B68GW9PwFU0onMKrS70kKE/43Vyo2E08QmCsqCYnXkGR5Nwzohzz2RhqT82eYD6Ec +R5ms3TKVu9NYv4It5nzVBs0PAOWjK7h9IX99rOv5QR2j3M7xyJ+FOOvzDmPDlP2YCL+Ir scRNHrN1Q0mjalav6uXeW8rmPJ8RWwQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1627625343; h=from:from: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=yJ1yHepxiXGKkkLe9+dCqnP+TH4u121Dr/zgR8/UQ4o=; b=elmUwU/oy3Wiei721hct2JCqOru8absqb4s/VGNf2JugJzjWpfssezxvIDXtRnzRvgCLFl Phhskarx1WBfhOAw== 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 3655313BFA; Fri, 30 Jul 2021 06:08:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id FMjSOHuXA2HpAwAAMHmgww (envelope-from ); Fri, 30 Jul 2021 06:08:59 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 From: "NeilBrown" To: "Al Viro" Cc: "Josef Bacik" , "J. Bruce Fields" , "Christoph Hellwig" , "Chuck Lever" , "Chris Mason" , "David Sterba" , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-btrfs@vger.kernel.org Subject: Re: [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly In-reply-to: References: <162742539595.32498.13687924366155737575.stgit@noble.brown>, <20210728193536.GD3152@fieldses.org>, , Date: Fri, 30 Jul 2021 16:08:57 +1000 Message-id: <162762533738.21659.10411397768851876517@noble.neil.brown.name> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, 30 Jul 2021, Al Viro wrote: > On Wed, Jul 28, 2021 at 05:30:04PM -0400, Josef Bacik wrote: >=20 > > I don't think anybody has that many file systems. For btrfs it's a single > > file system. Think of syncfs, it's going to walk through all of the super > > blocks on the system calling ->sync_fs on each subvol superblock. Now th= is > > isn't a huge deal, we could just have some flag that says "I'm not real" = or > > even just have anonymous superblocks that don't get added to the global > > super_blocks list, and that would address my main pain points. >=20 > Umm... Aren't the snapshots read-only by definition? No, though they can be. subvols can be created empty, or duplicated from an existing subvol. Any subvol can be written, using copy-on-write of course. NeilBrown