[CRIU] OverlayFS Patch

[Pavel Emelyanov]

On 08/06/2015 04:50 PM, Filipe Brandenburger 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.

Ah, I see. I thought that the only bad thing we were fixing was the
wrong path shown in /proc/pid/fd.

> 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?

Yes, a comment in the fact that we can't even rely on stat()-ing the
file descriptor would be good, thanks.

-- Pavel