blkcg: implement blkcg_policy->on/offline_pd_fn() and blkcg_gq->online

Add two blkcg_policy methods, ->online_pd_fn() and ->offline_pd_fn(),
which are invoked as the policy_data gets activated and deactivated
while holding both blkcg and q locks.

Also, add blkcg_gq->online bool, which is set and cleared as the
blkcg_gq gets activated and deactivated.  This flag also is toggled
while holding both blkcg and q locks.

These will be used to implement hierarchical stats.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 40f5b9768aac..678e89ed8ecb 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -106,12 +106,17 @@ struct blkcg_gq {
         /* reference count */
         int                             refcnt;
 
+        /* is this blkg online? protected by both blkcg and q locks */
+        bool                            online;
+
         struct blkg_policy_data         *pd[BLKCG_MAX_POLS];
 
         struct rcu_head                 rcu_head;
 };
 
 typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
+typedef void (blkcg_pol_online_pd_fn)(struct blkcg_gq *blkg);
+typedef void (blkcg_pol_offline_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);
 
@@ -124,6 +129,8 @@ struct blkcg_policy {
 
         /* operations */
         blkcg_pol_init_pd_fn            *pd_init_fn;
+        blkcg_pol_online_pd_fn          *pd_online_fn;
+        blkcg_pol_offline_pd_fn         *pd_offline_fn;
         blkcg_pol_exit_pd_fn            *pd_exit_fn;
         blkcg_pol_reset_pd_stats_fn     *pd_reset_stats_fn;
 };