mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

[Jason Vas Dias]

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

Re: mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

[Jason Vas Dias]

Of course the solution was to have created the filesystem in the first
place with
'mkfs.btrfs -O ^extref' . Found this after some more googling ...
Shouldn't this be the default ?
Regards,
Jason

On 9/22/14, Jason Vas Dias <jason.vas.dias@gmail.com> wrote:
> 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
>

Re: mount BTRFS filesystems created with 3.8+ under 2.6.32 kernels ?

[Chuck Ebbert]

On Mon, 22 Sep 2014 19:07:39 +0100
Jason Vas Dias <jason.vas.dias@gmail.com> wrote:

> Of course the solution was to have created the filesystem in the first
> place with
> 'mkfs.btrfs -O ^extref' . Found this after some more googling ...
> Shouldn't this be the default ?

Even worse, your vendor might change the default, like Red Hat did in
RHEL 7. ext4 filesystems created by the installer, even very small ones,
get the 64bit feature enabled and can't be mounted in RHEL 6.5.