Linux filesystems accessible from FreeBSD 8-stable?

[Aaron]

On Fri, Sep 24, 2010 at 12:21, Leif Walsh <leif.walsh at gmail.com> wrote:
> On Fri, Sep 24, 2010 at 2:04 PM, krad <kraduk at gmail.com> wrote:
>> Im not 100% sure  (probably about 60% actually) but cant you mount ext4 as
>> ext2? From what i vaguly remember there will be some limitations but its
>> worth having a look
>
>  # mount -t ext2fs /dev/ad4p1 /mnt
> mount: /dev/ad4p1 : Invalid argument
>
> Unless there's something I'm missing, nope.  ext3 works because the
> only difference between it and ext2 is the journal, I believe the
> on-disk format of ext4 is different (though maybe I'm wrong and the
> bsd drivers for ext2 just are too conservative?).
>
> --
> Cheers,
> Leif
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Doesn't look like you can mount an ext4 as ext2/3 if you have extents
enabled, which is probably enabled by default if you create a new
filesystem.

>From https://ext4.wiki.kernel.org/index.php/Frequently_Asked_Questions#Can_I_mount_existing_Ext3_as_Ext4.3F_And_vice_versa.3F_Similarly_from_Ext2_to_Ext4_and_its_reverse.3F

"Once you have enabled extents or created a journal on a former ext2
filesystem, it is an ext4 filesystem and cannot be reverted to ext2."

>From http://en.wikipedia.org/wiki/Ext4#Features
Under "Backward compatibility" header
"However, if the ext4 partition uses extents (a major new feature of
ext4), then the ability to mount the file system as ext3 is lost.

--Aaron