cgroup: add subsys backlink pointer to cftype

cgroup is transitioning to using css (cgroup_subsys_state) instead of
cgroup as the primary subsystem handle.  The cgroupfs file interface
will be converted to use css's which requires finding out the
subsystem from cftype so that the matching css can be determined from
the cgroup.

This patch adds cftype->ss which points to the subsystem the file
belongs to.  The field is initialized while a cftype is being
registered.  This makes it unnecessary to explicitly specify the
subsystem for other cftype handling functions.  @ss argument dropped
from various cftype handling functions.

This patch shouldn't introduce any behavior differences.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 1 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 79fd9f4fadb7..34063739745b 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1128,7 +1128,7 @@ void blkcg_policy_unregister(struct blkcg_policy *pol)
 
         /* kill the intf files first */
         if (pol->cftypes)
-                cgroup_rm_cftypes(&blkio_subsys, pol->cftypes);
+                cgroup_rm_cftypes(pol->cftypes);
 
         /* unregister and update blkgs */
         blkcg_policy[pol->plid] = NULL;