linux-ext4 - mount ext2/3 as ext4 - no changes to ext2/3 fs structures?

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Message-Id: <88FF0BDF-9F6F-4A2D-A236-C388BFFA145D@kupper.org>
Date:	Sun, 31 Jan 2010 23:31:03 +0100
From:	Thomas Kupper <thomas@...per.org>
To:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: mount ext2/3 as ext4 - no changes to ext2/3 fs structures?

Hello,

I guess it's a very simple question which I could not find a clear answer on the net: The ext4 wiki states that since 2.6.29 one can mount ext2/3 as ext4 without any changes.

Consider the following scenario: Assume I have a partition formated with ext2 on a computer with some 2.4.x kernel. Now I mount this ext2 partition on another computer as ext4 using a 2.6.29+ kernel. After that I take the disk back to the older computer and mount the ext2 on the 2.4.x kernel with the ext2 driver.

Does that work? Or is the ext4 driver updating some internal structures in a way that an old ext2 driver can't handle that partition anymore? Assume I  don't enable any ext4 specific features like extents, etc.

Thanks for any clarification or pointing to a doc that does,
Thomas--
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