5269 zfs: zpool import slow
PORTING: this code relies on the property of taskq_wait to wait
until no more tasks are queued and no more tasks are active. As
we always queue new tasks from within other tasks, task_wait
reliably waits for the full recursion to finish, even though we
enqueue new tasks after taskq_wait has been called.
On platforms other than illumos, taskq_wait may not have this
property.
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 176,185 ****
--- 176,205 ----
                          return (mvd);
  
          return (NULL);
  }
  
+ static int
+ vdev_count_leaves_impl(vdev_t *vd)
+ {
+         int n = 0;
+ 
+         if (vd->vdev_ops->vdev_op_leaf)
+                 return (1);
+ 
+         for (int c = 0; c < vd->vdev_children; c++)
+                 n += vdev_count_leaves_impl(vd->vdev_child[c]);
+ 
+         return (n);
+ }
+ 
+ int
+ vdev_count_leaves(spa_t *spa)
+ {
+         return (vdev_count_leaves_impl(spa->spa_root_vdev));
+ }
+ 
  void
  vdev_add_child(vdev_t *pvd, vdev_t *cvd)
  {
          size_t oldsize, newsize;
          uint64_t id = cvd->vdev_id;