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 5E1D0C4332F for ; Tue, 15 Nov 2022 18:13:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229772AbiKOSNk (ORCPT ); Tue, 15 Nov 2022 13:13:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32990 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229495AbiKOSNh (ORCPT ); Tue, 15 Nov 2022 13:13:37 -0500 Received: from zmcc-3-mx.zmailcloud.com (zmcc-3-mx.zmailcloud.com [34.200.143.36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86D5928E22 for ; Tue, 15 Nov 2022 10:13:35 -0800 (PST) Received: from zmcc-3.zmailcloud.com (183.87.154.104.bc.googleusercontent.com [104.154.87.183]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by zmcc-3-mx.zmailcloud.com (Postfix) with ESMTPS id CDA6A4056D for ; Tue, 15 Nov 2022 12:17:27 -0600 (CST) Received: from zmcc-3.zmailcloud.com (localhost [127.0.0.1]) by zmcc-3-mta-1.zmailcloud.com (Postfix) with ESMTPS id A3B5480366A0 for ; Tue, 15 Nov 2022 12:13:34 -0600 (CST) Received: from localhost (localhost [127.0.0.1]) by zmcc-3-mta-1.zmailcloud.com (Postfix) with ESMTP id 94B0F80366A1 for ; Tue, 15 Nov 2022 12:13:34 -0600 (CST) Received: from zmcc-3.zmailcloud.com ([127.0.0.1]) by localhost (zmcc-3-mta-1.zmailcloud.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id ZbSpYKqGvzaQ for ; Tue, 15 Nov 2022 12:13:34 -0600 (CST) Received: from [10.4.2.11] (unknown [37.19.198.182]) by zmcc-3-mta-1.zmailcloud.com (Postfix) with ESMTPSA id 45F9280366A0 for ; Tue, 15 Nov 2022 12:13:34 -0600 (CST) Date: Tue, 15 Nov 2022 13:13:27 -0500 From: Eric Levy Subject: Re: property designating root subvolumes To: linux-btrfs Message-Id: In-Reply-To: <6e932071-ef89-0d69-550f-755abea004ba@gmail.com> References: <6e932071-ef89-0d69-550f-755abea004ba@gmail.com> X-Mailer: geary/40.0 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Nov 15 2022 at 08:50:50 PM +0300, Andrei Borzenkov wrote: > On 15.11.2022 02:23, Eric Levy wrote: >> The file system allows one subvolume per partition to be designated >> as >> the default, and no more than one would be sensible. Generally, for > > It is not partition, it is filesystem. I'm sorry, but I fail to understand any distinction from your comment that clarifies a genuine confusion, within the present context, more than a semantic nuance. >> So far the only usage proposed by you is to scan btrfs subvolumes to >> apparently present user multiple choices during boot. Any bootloader >> that understands btrfs enough to read subvolume properties can also >> read information inside subvolume to achieve the same effect. You >> need to prepare subvolume anyway. A bootloader may not be the best location to include logic for descending into a subvolume, to resolve whether it contains a root file hierarchy. Meanwhile, some subvolumes, such a snapshots, may appear internally as root subvolumes, though not being desired for entries on a boot menu. Presently, it is worth considering the historic precedent that the default subvolume is being used to identify a location for a root file hierarchy. The association often holds, but is not the basis of any fully robust assumption. > If you suggest some other usage I am afraid I failed to understand it. I will let others express whether they understand more clearly.