From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from slmp-550-94.slc.westdc.net ([50.115.112.57]:11113 "EHLO slmp-550-94.slc.westdc.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751950Ab3ESSSX convert rfc822-to-8bit (ORCPT ); Sun, 19 May 2013 14:18:23 -0400 Received: from c-67-165-243-162.hsd1.co.comcast.net ([67.165.243.162]:53044 helo=[192.168.1.126]) by slmp-550-94.slc.westdc.net with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.80) (envelope-from ) id 1Ue8Ba-0012Wk-0c for linux-btrfs@vger.kernel.org; Sun, 19 May 2013 12:18:22 -0600 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 6.3 \(1503\)) Subject: Re: Virtual Device Support From: Chris Murphy In-Reply-To: <20130519171510.54897415@natsu> Date: Sun, 19 May 2013 12:18:19 -0600 Message-Id: <262CC063-0DB4-45BD-A776-9FD1E8650E7C@colorremedies.com> References: <518CFE3A.3080900@chinilu.com> <20130519171510.54897415@natsu> To: Btrfs BTRFS Sender: linux-btrfs-owner@vger.kernel.org List-ID: On May 19, 2013, at 5:15 AM, Roman Mamedov wrote: > On Fri, 10 May 2013 07:03:38 -0700 > George Mitchell wrote: > >> One the things that is frustrating me the most at this point from a user >> perspective regarding btrfs is the current lack of virtual devices to >> describe volumes and subvolumes. > > From a user perspective btrfs subvolumes have a lot in common with just > regular directories aka folders, and nothing in common with (block)devices. > "Describing them with virtual devices" does not seem to make a whole lot of > sense. It's not possible to mount regular directories with other file systems. In some ways the btrfs subvolume behaves like a folder. In other ways it acts like a device. If you stat the mount point for btrfs subvolumes, you get a unique device ID for each. It seems inconsistent that mount and unmount allows a /dev/ designation, but only mount honors label and UUID. I can mount with mount /dev/disk/by-uuid/xxxxxxx, but if I use umount /dev/disk/by-uuid/xxxxxxxx I get a bogus error: umount: /dev/disk/by-uuid/xxxxxxxxxx: not mounted mount /dev/disk/by-uuid will autocomplete/list uuids in that directory, umount will not. So just from a consistency standpoint that seems broken. Chris Murphy