[CRIU] OverlayFS Patch

[Saied Kazemi]

On Thu, Aug 6, 2015 at 6:50 AM, Filipe Brandenburger <filbranden at google.com>
wrote:

> On Thu, Aug 6, 2015 at 2:14 AM, Pavel Emelyanov <xemul at parallels.com>
> wrote:
> > On 08/06/2015 02:21 AM, Gabriel Guimaraes wrote:
> >> So I just tested it and it turns out that, because of the Kernel bug,
> statfs returns ext2/ext3 instead
> >> of OVERLAYFS_MAGIC when used on a symlink to a file in an OVFs
> directory, so we can't rely on that.
> >
> > I see :) Yet another patch idea for the kernel.
>
> Not really though...
>
> As of kernel 4.2-rc2, all the kernel overlayfs bugs are fixed (in
> particular the ones fixing the paths of the symlinks under
> /proc/*/fd/*), so on that kernel version criu without this patchset
> works to checkpoint/restore containers using overlayfs.
>
> This patch is meant to work around the bugs present in 3.18ish up to
> 4.2 when the issue has been resolved.
>
> If we could go back in time to have a kernel patch applied, we should
> instead apply the patchset that actually fixed the issue in 4.2 :-)
>
> The patches that fixed the overlayfs issues are listed here:
> http://criu.org/Docker#OverlayFS and I believe Ubuntu Vivid might get
> these backports into their 3.19.
>
> Gabriel's code will work properly on both the kernel with and without the
> fixes.
>
> Not sure if this was clear from the original submission... Perhaps in
> light of these facts you'd like to have some comments or commit
> descriptions rephrased to indicate that this code is there to support
> kernels in that version range?
>
> Cheers!
> Filipe
>

To be completely clear:

1. The good news is that the OverlayFS bugs will be fixed in the next
Ubuntu Vivid kernel because I filed a bug and Chris Arges of Canonical
reproduced the problem and also verified that the patches I had mentioned
fix the issues.  For details please see:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1479468

2. In the meantime, Ubuntu Vivid users can install a 3.19 kernel with
OvelayFS bugs fixed from CRIU PPA:
https://launchpad.net/~criu/+archive/ubuntu/ppa

3. Users of other distros, however, will continue to have this bug until
they upgrade their kernel to 4.2 or back port the patches.

--Saied
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