cgroup: merge cft_release_agent cftype array into the base files array

Now that cftype can express whether a file should only be on root,
cft_release_agent can be merged into the base files cftypes array.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>

kernel/cgroup.c

@@ -3732,13 +3732,13 @@ static struct cftype files[] = {
 		.read_u64 = cgroup_clone_children_read,
 		.write_u64 = cgroup_clone_children_write,
 	},
-};
-
-static struct cftype cft_release_agent = {
+	{
 		.name = "release_agent",
+		.flags = CFTYPE_ONLY_ON_ROOT,
 		.read_seq_string = cgroup_release_agent_show,
 		.write_string = cgroup_release_agent_write,
 		.max_write_len = PATH_MAX,
+	},
 };
 
 static int cgroup_populate_dir(struct cgroup *cgrp)
@@ -3750,11 +3750,6 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
 	if (err < 0)
 		return err;
 
-	if (cgrp == cgrp->top_cgroup) {
-		if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
-			return err;
-	}
-
 	/* process cftsets of each subsystem */
 	for_each_subsys(cgrp->root, ss) {
 		struct cftype_set *set;