From: Andreas Dilger Subject: Re: [PATCH 2/4] e2fsprogs: Add undoe2fs Date: Wed, 1 Aug 2007 02:10:32 -0500 Message-ID: <20070801071032.GQ5469@schatzie.adilger.int> References: <47f96570519d76b8d59f92b729a0a48c4a1b68d8.1185933778.git.aneesh.kumar@linux.vnet.ibm.com> <20070801060211.GO5469@schatzie.adilger.int> <46B02539.5020505@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: tytso@mit.edu, linux-ext4@vger.kernel.org To: "Aneesh Kumar K.V" Return-path: Received: from mail.clusterfs.com ([74.0.229.162]:39012 "EHLO mail.clusterfs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751874AbXHAHKf (ORCPT ); Wed, 1 Aug 2007 03:10:35 -0400 Content-Disposition: inline In-Reply-To: <46B02539.5020505@linux.vnet.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Aug 01, 2007 11:46 +0530, Aneesh Kumar K.V wrote: > Andreas Dilger wrote: > >On Aug 01, 2007 07:34 +0530, Aneesh Kumar K.V wrote: > >>undoe2fs can be used to replay the transaction saved > >>in the transaction file using undo I/O Manager > > > >This should save the mtime of the superblock, and only do the undo > >step if the filesystem hasn't changed. Otherwise it could seriously > >corrupt the filesystem. > > I am not sure i understand this. The Undo I/O manager tracks all the write > happening to the file system and copy the original content of the blocks to > the tdb file. Undoe2fs simply copies these blocks back to the file system. > > That way if you look at undoe2fs it doesn't have any knowledge of the file > system at all. > > Can you let me know a use case where this will fail. - modify filesystem with undo manager (e.g. inode resize) - mount filesystem, make changes, unmount - run undoe2fs to overwrite filesystem, corrupting it Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc.