blkcg: add blkcg->id

Add 64bit unique id to blkcg.  This will be used by policies which
want blkcg identity test to tell whether the associated blkcg has
changed.

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

2 files changed, 6 insertions, 0 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b15a51711bca..30e07308db24 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -19,6 +19,7 @@
 #include <linux/slab.h>
 #include <linux/genhd.h>
 #include <linux/delay.h>
+#include <linux/atomic.h>
 #include "blk-cgroup.h"
 #include "blk.h"
 
@@ -1622,6 +1623,7 @@ static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)
 static struct cgroup_subsys_state *
 blkiocg_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
 {
+        static atomic64_t id_seq = ATOMIC64_INIT(0);
         struct blkio_cgroup *blkcg;
         struct cgroup *parent = cgroup->parent;
 
@@ -1635,6 +1637,7 @@ blkiocg_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
                 return ERR_PTR(-ENOMEM);
 
         blkcg->weight = BLKIO_WEIGHT_DEFAULT;
+        blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
 done:
         spin_lock_init(&blkcg->lock);
         INIT_HLIST_HEAD(&blkcg->blkg_list);
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 9df5ab04b6d6..1cb8f7643258 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -116,6 +116,9 @@ struct blkio_cgroup {
         unsigned int weight;
         spinlock_t lock;
         struct hlist_head blkg_list;
+
+        /* for policies to test whether associated blkcg has changed */
+        uint64_t id;
 };
 
 struct blkio_group_stats {