From: Dexuan Cui Subject: RE: Is ext2 freezable? Date: Fri, 19 Sep 2014 03:11:40 +0000 Message-ID: References: <20140918191736.GC19520@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT Cc: "linux-ext4@vger.kernel.org" To: Theodore Ts'o Return-path: Received: from mail-bl2on0105.outbound.protection.outlook.com ([65.55.169.105]:8512 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754532AbaISDM2 convert rfc822-to-8bit (ORCPT ); Thu, 18 Sep 2014 23:12:28 -0400 In-Reply-To: <20140918191736.GC19520@thunk.org> Content-Language: en-US Sender: linux-ext4-owner@vger.kernel.org List-ID: > -----Original Message----- > From: Theodore Ts'o [mailto:tytso@mit.edu] > Sent: Friday, September 19, 2014 3:18 AM > To: Dexuan Cui > Cc: linux-ext4@vger.kernel.org > Subject: Re: Is ext2 freezable? > > On Thu, Sep 18, 2014 at 06:46:21AM +0000, Dexuan Cui wrote: > > > > I've got the answer: > > ext2.ko itself does support fsfreeze, but typical linux distros don't supply > > ext2.ko at all now -- instead, they usually supply ext3.ko and have ext4 > builtin. > > > > So when I mount an ext2 partition, actually the kernel is registering the ext4 > > driver as an ext2 driver and in this case the ext2's s_op->freeze_fs is NULL -- > > but, why did ext4 choose this behavior for ext2? > > It wasn't a deliberate design choice. It was just that when > no-journal mode was added to ext4, freeeze support was never > implemented, and up until now, no one had asked for it. We can add it > to ext4; thanks for calling it to our attention. > - Ted Hi Ted, Thanks very much for the clarification! And thanks a lot for implementing this -- I've seen the patches you sent out several hours ago. IMO it's useful to have such compatibility, e.g., Hyper-V guest has a fsfreeze-based feature to back up the data; the feature works fine for ext4 partition, but Ubuntu's installer can create /boot of ext2 partition by default and hence the feature can't work: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1362574 I believe the bug will go away after Ubuntu integrates your patches. Thanks! -- Dexuan