linux-ext4 - Re: Mounting Ext3 with Ext4

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Message-ID: <baab8ccb0905201828i7ad6536ele72157b3e2d223c1@mail.gmail.com>
Date:	Wed, 20 May 2009 21:28:30 -0400
From:	Matt LaPlante <cybrmatt@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Mounting Ext3 with Ext4

On Wed, May 20, 2009 at 9:17 PM, Eric Sandeen <sandeen@...hat.com> wrote:
> Matt LaPlante wrote:
>> According to the Ext4 howto
>> (http://ext4.wiki.kernel.org/index.php/Ext4_Howto#Converting_an_ext3_filesystem_to_ext4),
>> "It is possible to mount both ext3 (and ext2, in kernels 2.6.28 and
>> later) filesystems directly using the ext4 filesystem driver."  So
>> this means, if I'm reading it correctly, that a kernel built with ext4
>> support should be able to mount and manage ext[234] filesystems.  Is
>> that correct?  If so, are there any limitations on this support?
>>
>> I'm running Ubuntu Jaunty with some custom-built 2.6.29.4 kernels and
>> grub2.  I seem to have no problem booting from ext4 disks, so the ext4
>> support is definitely there and functioning.  I had hoped the ext3
>> support meant I could build the kernel with ext4 only and carry on as
>> usual with my ext3 partitions.  Unfortunately doing so causes the ext3
>> partitions to fail to boot.  So...
>>
>> booting ext3 with ext3 in the kernel=fine
>> booting ext4 with ext4 in the kernel=fine
>> booting ext3 with ext4 (only) in the kernel=not fine
>>
>> Is this a problem or was it never intended to work?
>
> It should work...
>
> It'd be more helpful if you could include details on exactly how it
> failed, but if Ubuntu builds ext4 as a module, perhaps the initrd
> creation sees root as ext3 and doesn't bother to put ext4 in the initrd?

ext4 was compiled in directly, it was not a module (this wasn't an
ubuntu kernel; it was stock).  I can try to get a stack trace with
netconsole if it gets far enough to function.

>
> -Eric
>
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