linux-kernel - mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

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Message-ID: <CALyZvKz4gyH64an3NWz2zY4b0NN34LwSME-oD8-Vw+e1SCF0Nw@mail.gmail.com>
Date:	Mon, 22 Sep 2014 17:44:26 +0100
From:	Jason Vas Dias <jason.vas.dias@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

Good day -

I wonder if there is a GIT repository somewhere with a backport of the BTRFS
kernel modules  that will allow BTRFS filesystems created with a 3.8 kernel to
be mounted on a 2.6.32+ kernel .

When I try this, the 2.6.32 kernel crashes with the message :
 'BTRFS: couldn't mount because of unsupported optional features (40)'
( kernel-2.6.32-431.29.2.el6.x86_64 from RHEL 6.4+ ).

The same filesystem mounts fine under Oracle EL6 which now comes with
kernel-uek 3.8+ .  Has anyone tried to backport the 3.8 BTRFS
capabilities to 2.6.32 ,
or is there any way I can remove "Option 40" to get it to mount
without crashing ?
It is a very small BTRFS filesystem with a root filesystem and a few snapshots.
I did not specify any BTRFS options in :
  $ mkfs.btrfs /dev/sda9;
  ... # mount on /mnt/btr & create some files
  $ btrfs subvolume snapshot -r /mnt/btr /mnt/btr/root-0
  $ btrfs subvolume snapshot    /mnt/btr /mnt/btr/root-w-0
Now I can mount /dev/sda9 under any 3.8+ kernel, but not under 2.6.32 .

Thanks in advance for any replies,
Best Regards, Jason Vas Dias
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