cgroup: convert memcg controller to the new cftype interface

Convert memcg to use the new cftype based interface.  kmem support
abuses ->populate() for mem_cgroup_sockets_init() so it can't be
removed at the moment.

tcp_memcontrol is updated so that tcp_files[] is registered via a
__initcall.  This change also allows removing the forward declaration
of tcp_files[].  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Greg Thelen <gthelen@google.com>

mm/memcontrol.c

@@ -4764,6 +4764,7 @@ static struct cftype mem_cgroup_files[] = {
 		.read = mem_cgroup_read,
 	},
 #endif
+	{ },	/* terminate */
 };
 
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
@@ -5041,15 +5042,7 @@ static void mem_cgroup_destroy(struct cgroup *cont)
 static int mem_cgroup_populate(struct cgroup_subsys *ss,
 				struct cgroup *cont)
 {
-	int ret;
-
-	ret = cgroup_add_files(cont, ss, mem_cgroup_files,
-				ARRAY_SIZE(mem_cgroup_files));
-
-	if (!ret)
-		ret = register_kmem_files(cont, ss);
-
-	return ret;
+	return register_kmem_files(cont, ss);
 }
 
 #ifdef CONFIG_MMU
@@ -5639,6 +5632,7 @@ struct cgroup_subsys mem_cgroup_subsys = {
 	.can_attach = mem_cgroup_can_attach,
 	.cancel_attach = mem_cgroup_cancel_attach,
 	.attach = mem_cgroup_move_task,
+	.base_cftypes = mem_cgroup_files,
 	.early_init = 0,
 	.use_id = 1,
 };

net/ipv4/tcp_memcontrol.c

@@ -6,8 +6,6 @@
 #include <linux/memcontrol.h>
 #include <linux/module.h>
 
-static struct cftype tcp_files[4];	/* XXX: will be removed soon */
-
 static inline struct tcp_memcontrol *tcp_from_cgproto(struct cg_proto *cg_proto)
 {
 	return container_of(cg_proto, struct tcp_memcontrol, cg_proto);
@@ -36,7 +34,7 @@ int tcp_init_cgroup(struct cgroup *cgrp, struct cgroup_subsys *ss)
 
 	cg_proto = tcp_prot.proto_cgroup(memcg);
 	if (!cg_proto)
-		goto create_files;
+		return 0;
 
 	tcp = tcp_from_cgproto(cg_proto);
 
@@ -59,9 +57,7 @@ int tcp_init_cgroup(struct cgroup *cgrp, struct cgroup_subsys *ss)
 	cg_proto->sockets_allocated = &tcp->tcp_sockets_allocated;
 	cg_proto->memcg = memcg;
 
-create_files:
-	return cgroup_add_files(cgrp, ss, tcp_files,
-				ARRAY_SIZE(tcp_files));
+	return 0;
 }
 EXPORT_SYMBOL(tcp_init_cgroup);
 
@@ -266,4 +262,12 @@ static struct cftype tcp_files[] = {
 		.trigger = tcp_cgroup_reset,
 		.read_u64 = tcp_cgroup_read,
 	},
+	{ }	/* terminate */
 };
+
+static int __init tcp_memcontrol_init(void)
+{
+	WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys, tcp_files));
+	return 0;
+}
+__initcall(tcp_memcontrol_init);