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>

*** 152,161 ****
--- 152,162 ----
  void dsl_pool_mos_diduse_space(dsl_pool_t *dp,
      int64_t used, int64_t comp, int64_t uncomp);
  void dsl_pool_config_enter(dsl_pool_t *dp, void *tag);
  void dsl_pool_config_exit(dsl_pool_t *dp, void *tag);
  boolean_t dsl_pool_config_held(dsl_pool_t *dp);
+ boolean_t dsl_pool_config_held_writer(dsl_pool_t *dp);
  boolean_t dsl_pool_need_dirty_delay(dsl_pool_t *dp);
  
  taskq_t *dsl_pool_vnrele_taskq(dsl_pool_t *dp);
  
  int dsl_pool_user_hold(dsl_pool_t *dp, uint64_t dsobj,