cgroups: blkio subsystem as module

Modify the Block I/O cgroup subsystem to be able to be built as a module.
As the CFQ disk scheduler optionally depends on blk-cgroup, config options
in block/Kconfig, block/Kconfig.iosched, and block/blk-cgroup.h are
enhanced to support the new module dependency.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 41 insertions, 12 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c85d74cae200..4b686ad08eaa 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -23,6 +23,31 @@ static LIST_HEAD(blkio_list);
 struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
 EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
+static struct cgroup_subsys_state *blkiocg_create(struct cgroup_subsys *,
+                                                  struct cgroup *);
+static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *,
+                              struct task_struct *, bool);
+static void blkiocg_attach(struct cgroup_subsys *, struct cgroup *,
+                           struct cgroup *, struct task_struct *, bool);
+static void blkiocg_destroy(struct cgroup_subsys *, struct cgroup *);
+static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
+
+struct cgroup_subsys blkio_subsys = {
+        .name = "blkio",
+        .create = blkiocg_create,
+        .can_attach = blkiocg_can_attach,
+        .attach = blkiocg_attach,
+        .destroy = blkiocg_destroy,
+        .populate = blkiocg_populate,
+#ifdef CONFIG_BLK_CGROUP
+        /* note: blkio_subsys_id is otherwise defined in blk-cgroup.h */
+        .subsys_id = blkio_subsys_id,
+#endif
+        .use_id = 1,
+        .module = THIS_MODULE,
+};
+EXPORT_SYMBOL_GPL(blkio_subsys);
+
 struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
 {
         return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
@@ -253,7 +278,8 @@ remove_entry:
 done:
         free_css_id(&blkio_subsys, &blkcg->css);
         rcu_read_unlock();
-        kfree(blkcg);
+        if (blkcg != &blkio_root_cgroup)
+                kfree(blkcg);
 }
 
 static struct cgroup_subsys_state *
@@ -319,17 +345,6 @@ static void blkiocg_attach(struct cgroup_subsys *subsys, struct cgroup *cgroup,
         task_unlock(tsk);
 }
 
-struct cgroup_subsys blkio_subsys = {
-        .name = "blkio",
-        .create = blkiocg_create,
-        .can_attach = blkiocg_can_attach,
-        .attach = blkiocg_attach,
-        .destroy = blkiocg_destroy,
-        .populate = blkiocg_populate,
-        .subsys_id = blkio_subsys_id,
-        .use_id = 1,
-};
-
 void blkio_policy_register(struct blkio_policy_type *blkiop)
 {
         spin_lock(&blkio_list_lock);
@@ -345,3 +360,17 @@ void blkio_policy_unregister(struct blkio_policy_type *blkiop)
         spin_unlock(&blkio_list_lock);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_unregister);
+
+static int __init init_cgroup_blkio(void)
+{
+        return cgroup_load_subsys(&blkio_subsys);
+}
+
+static void __exit exit_cgroup_blkio(void)
+{
+        cgroup_unload_subsys(&blkio_subsys);
+}
+
+module_init(init_cgroup_blkio);
+module_exit(exit_cgroup_blkio);
+MODULE_LICENSE("GPL");