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Date:	Wed, 1 Aug 2007 02:10:32 -0500
From:	Andreas Dilger <adilger@...sterfs.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/4] e2fsprogs: Add undoe2fs

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.

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