Currently may_access() is only able to verify if an exception is valid for the
current cgroup, which has the same behavior. With hierarchy, it'll be also used
to verify if a cgroup local exception is valid towards its cgroup parent, which
might have different behavior.
v2:
- updated patch description
- rebased on top of a new patch to expand the may_access() logic to make it
more clear
- fixed argument description order in may_access()