From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from outrelay01.libero.it ([212.52.84.101]:56619 "EHLO outrelay01.libero.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755754Ab2FTMCg (ORCPT ); Wed, 20 Jun 2012 08:02:36 -0400 Message-ID: <32353828.234981340193742067.JavaMail.defaultUser@defaultHost> Date: Wed, 20 Jun 2012 14:02:22 +0200 (CEST) From: "Goffredo Baroncelli " Reply-To: "Goffredo Baroncelli " To: , cwillu Subject: R: Re: Subvolumes and /proc/self/mountinfo Cc: , MIME-Version: 1.0 Content-Type: text/plain;charset="UTF-8" Sender: linux-btrfs-owner@vger.kernel.org List-ID: HI all, >----Messaggio originale---- >Da: hpa@zytor.com >Data: 20/06/2012 5.22 >A: "cwillu" >Cc: , >Ogg: Re: Subvolumes and /proc/self/mountinfo > > >The concept of what is the "root" and what is the "path" is >straightforward for lesser filesystems: the root of the filesystem is >defined by the root inode, and the path is a unique sequence of >directories from that root. Note that this is completely independent of >how the filesystem was mounted when the boot loader was installed. For the aim of the discussion, I would like to highlight a small difference between the path of the subvolume and the subvolume-id. The latter is the specific subvolume, the former is a "functional" reference to this subvolume. For example, in my root btrfs I have two two subvolumes: __active (the root filesystem of my system) and (__rollback the last "good" copy) If I swap (via a rename) __active and __rollback, in the next boot my system uses a "good" copy of the root filesystem. This is a simple way to swap two subvolumes, without involving the boot logic Instead if I had tracked the subvolume-id, to swap the root filesystem I would have update the boot logic. I suspect that could exists other cases where it is preferable to track the subvolume-id instead the path. However what I would highlight it is the two ways aren't equal. BR G.Baroncelli