cgroup: make cgroup_css() take cgroup_subsys * instead and allow NULL subsys

cgroup_css() is no longer used in hot paths.  Make it take struct
cgroup_subsys * and allow the users to specify NULL subsys to obtain
the dummy_css.  This removes open-coded NULL subsystem testing in a
couple users and generally simplifies the code.

After this patch, css_from_dir() also allows NULL @ss and returns the
matching dummy_css.  This behavior change doesn't affect its only user
- perf.

Signed-off-by: Tejun Heo <[email protected]>
Acked-by: Li Zefan <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>

0 files changed, 0 insertions, 0 deletions