[CRIU] [RFC] mount: Add ability to c/r devtmpfs

[Serge Hallyn]

Quoting Cyrill Gorcunov (gorcunov at gmail.com):
> On Thu, Oct 16, 2014 at 08:57:40PM +0000, Serge Hallyn wrote:
> > Quoting Cyrill Gorcunov (gorcunov at openvz.org):
> > > Looking into experiments with OpenVZ kernel
> > > it seems plain tar over devtmpfs should be
> > > enough for a while. So here is a new option
> > > comes in "--devtmpfs-content".
> > 
> > Hi - so I'm pretty sure this is the case, but just want to make 100%
> > sure, and looking at the criu git HEAD didn't help me - when this
> > gets restore, it will be mounted as tmpfs right?  (not devtmpfs, I
> > hope?)
> 
> Hi, Serge! It's mounted as devtmpfs on restore and the option
> --devtmpfs-content simply untar devices to newly mounted fs.
> Because in vanilla kernel devtmpfs is not virtualized at all
> this option is mostly for custom kernels such as openvz (or
> any other which implements devtmpfs virtualization). IOW,
> it's not a common case but I need it for openvz case.

Can you detect the openvz kernel and refuse the untar if on
upstream kernel?  You can really screw up the host otherwise...