cgroup: helper do determine group name

With more than one user, it is useful to have a helper function in the
cgroup core to derive a group's name.

We'll just return a pointer, and it is not expected to get incredibly
complicated. But it is useful to have it so we can abstract away the
vfs relation from its users.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Tejun Heo <tj@kernel.org>
CC: Michal Hocko <mhocko@suse.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Johannes Weiner <hannes@cmpxchg.org>
3 files changed