From: Dexuan Cui Subject: RE: Is ext2 freezable? Date: Thu, 18 Sep 2014 06:46:21 +0000 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT To: "linux-ext4@vger.kernel.org" Return-path: Received: from mail-bn1bbn0104.outbound.protection.outlook.com ([157.56.111.104]:2784 "EHLO na01-bn1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751313AbaIRGqk convert rfc822-to-8bit (ORCPT ); Thu, 18 Sep 2014 02:46:40 -0400 Content-Language: en-US Sender: linux-ext4-owner@vger.kernel.org List-ID: > -----Original Message----- > From: Dexuan Cui > Sent: Thursday, September 18, 2014 13:16 PM > To: linux-ext4@vger.kernel.org > Subject: Is ext2 freezable? > > Hi all, > I'm running "fsfreeze --freeze /mnt" (/mnt is mounted with an ext2 partition) > and getting "fsfreeze: /mnt: freeze failed: Operation not supported": > ... > code of ioctl_fsfreeze() is: > > static int ioctl_fsfreeze(struct file *filp) > { > struct super_block *sb = file_inode(filp)->i_sb; > > if (!capable(CAP_SYS_ADMIN)) > return -EPERM; > > /* If filesystem doesn't support freeze feature, return. */ > if (sb->s_op->freeze_fs == NULL) > return -EOPNOTSUPP; > > /* Freeze */ > return freeze_super(sb); > } > > It seems here sb->s_op->freeze_fs is NULL??? why? 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? Thanks, -- Dexuan