[libvirt] [RFC][PATCH] lxc: fix for ns cgroups subsystem

[Serge E. Hallyn]

Quoting Ryota Ozaki (ozaki.ryota at gmail.com):
> I've updated the patch. The change includes support for multiple mount
> points of cgroups that I didn't cope with in the previous patch.
> 
> Through the work, I found a bit messy problem. Current lxc controller writes
> pid in a 'tasks' file multiple times if one mount point has multiple subsystems.
> It is bad because the first write changes the cgroups path of a controller, and
> then the second write points a missing file like
> $CGROUPS_MOUNTPOINT/<path_to_domain>/<path_to_domain>/tasks where
> the correct file is $CGROUPS_MOUNTPOINT/<path_to_domain>/tasks.
> I did workaround this problem with a tricky way by truncating the
> duplicated path.
> We probably need a more feasible solution.

Seems like the loop in virCgroupAddTask() should just keep track
of which hierarchies it has already written to.  Just a small
temporary hash table or for that matter a small array that you
walk linearly...

-serge