[CRIU] OverlayFS Patch

[Filipe Brandenburger]

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