cgroup: make cgroup_css() take cgroup_subsys * instead and allow NULL subsys
authorTejun Heo <tj@kernel.org>
Mon, 26 Aug 2013 22:40:56 +0000 (18:40 -0400)
committerTejun Heo <tj@kernel.org>
Mon, 26 Aug 2013 22:40:56 +0000 (18:40 -0400)
commitca8bdcaff0d77990fb69e0f946018c96a70851cc
treeac98548b8fc61cf8017a67df9be6c5a4e87a6201
parent35cf083619da5677f83e9a8eae813f0b413d7082
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 <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
kernel/cgroup.c