blkcg: implement blkg_for_each_descendant_post()

This will be used by blk-throttle hierarchy support.

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

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 11f5b92..e15f731 100644 (file)
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -303,6 +303,20 @@ struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q,
                                              (p_blkg)->q, false)))
 
 /**
+ * blkg_for_each_descendant_post - post-order walk of a blkg's descendants
+ * @d_blkg: loop cursor pointing to the current descendant
+ * @pos_cgrp: used for iteration
+ * @p_blkg: target blkg to walk descendants of
+ *
+ * Similar to blkg_for_each_descendant_pre() but performs post-order
+ * traversal instead.  Synchronization rules are the same.
+ */
+#define blkg_for_each_descendant_post(d_blkg, pos_cgrp, p_blkg)                \
+       cgroup_for_each_descendant_post((pos_cgrp), (p_blkg)->blkcg->css.cgroup) \
+               if (((d_blkg) = __blkg_lookup(cgroup_to_blkcg(pos_cgrp), \
+                                             (p_blkg)->q, false)))
+
+/**
  * blk_get_rl - get request_list to use
  * @q: request_queue of interest
  * @bio: bio which will be attached to the allocated request (may be %NULL)