[CRIU] Restore into different cgroups

[Pavel Emelyanov]

On 08/12/2014 07:13 PM, Tycho Andersen wrote:

>> Doing regexp substitution in criu code would be confusing... I was 
>> thinking about treating all the paths as being relative to the init 
>> task's cgset and keep this task's full paths in the image. Then
>> introduce the --cgroup-root option that would override the init task's
>> path from the image.
>>
>> Would that work for you?
> 
> I don't understand exactly how that would work. It would just add a
> prefix, so --cgroup-root=/foo would rewrite /lxc/u1 to /foo/lxc/u1?
> What about other cgroups unrelated to the container? Can we avoid
> rewriting those?

OK, let me explain in more details what I mean.

Let's imagine we have init task living in /lxc/ct, some other task
in /lxc/ct/sub and there's also an empty subgroup /lxc/ct/empty.

When we dump this, in the image we'd get:

* root task lives in /lxc/ct
* "some other task" lives in /sub
* there's a subgroup called /sub
* there's a subgroup called /empty

On restore criu would prepend the /lxc/ct (path from root task)
to whatever path it meets in the cgroup image.

If we want to restore tasks into /lxc/ct2/lxc/ct, then we'd say on
restore --cgroup-root /lxc/ct2/lxc/ct and criu would prepend _this_
to all the other paths (except for the root task's, i.e. /lxc/ct
from the image would be ignored).

This will be so for every controller. Do we need per-controller
control? If can look like

--cgroup-root $path -- prepend $path for every controller
--cgroup-root $ctl:$path -- only for controller $ctl

and the option can be specified multiple times.

Thanks,
Pavel