4171 clean up spa_feature_*() interfaces
4172 implement extensible_dataset feature for use by other zpool features
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 561,580 ****
  }
  
  static int
  verify_spacemap_refcounts(spa_t *spa)
  {
!         int expected_refcount, actual_refcount;
  
!         expected_refcount = spa_feature_get_refcount(spa,
!             &spa_feature_table[SPA_FEATURE_SPACEMAP_HISTOGRAM]);
          actual_refcount = get_dtl_refcount(spa->spa_root_vdev);
          actual_refcount += get_metaslab_refcount(spa->spa_root_vdev);
  
          if (expected_refcount != actual_refcount) {
!                 (void) printf("space map refcount mismatch: expected %d != "
!                     "actual %d\n", expected_refcount, actual_refcount);
                  return (2);
          }
          return (0);
  }
  
--- 561,584 ----
  }
  
  static int
  verify_spacemap_refcounts(spa_t *spa)
  {
!         uint64_t expected_refcount = 0;
!         uint64_t actual_refcount;
  
!         (void) feature_get_refcount(spa,
!             &spa_feature_table[SPA_FEATURE_SPACEMAP_HISTOGRAM],
!             &expected_refcount);
          actual_refcount = get_dtl_refcount(spa->spa_root_vdev);
          actual_refcount += get_metaslab_refcount(spa->spa_root_vdev);
  
          if (expected_refcount != actual_refcount) {
!                 (void) printf("space map refcount mismatch: expected %lld != "
!                     "actual %lld\n",
!                     (longlong_t)expected_refcount,
!                     (longlong_t)actual_refcount);
                  return (2);
          }
          return (0);
  }
  
*** 672,683 ****
                  metaslab_unload(msp);
                  mutex_exit(&msp->ms_lock);
          }
  
          if (dump_opt['m'] > 1 && sm != NULL &&
!             spa_feature_is_active(spa,
!             &spa_feature_table[SPA_FEATURE_SPACEMAP_HISTOGRAM])) {
                  /*
                   * The space map histogram represents free space in chunks
                   * of sm_shift (i.e. bucket 0 refers to 2^sm_shift).
                   */
                  (void) printf("\tOn-disk histogram:\n");
--- 676,686 ----
                  metaslab_unload(msp);
                  mutex_exit(&msp->ms_lock);
          }
  
          if (dump_opt['m'] > 1 && sm != NULL &&
!             spa_feature_is_active(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM)) {
                  /*
                   * The space map histogram represents free space in chunks
                   * of sm_shift (i.e. bucket 0 refers to 2^sm_shift).
                   */
                  (void) printf("\tOn-disk histogram:\n");
*** 2464,2475 ****
              count_block_cb, &zcb, NULL);
          if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
                  (void) bpobj_iterate_nofree(&spa->spa_dsl_pool->dp_free_bpobj,
                      count_block_cb, &zcb, NULL);
          }
!         if (spa_feature_is_active(spa,
!             &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
                  VERIFY3U(0, ==, bptree_iterate(spa->spa_meta_objset,
                      spa->spa_dsl_pool->dp_bptree_obj, B_FALSE, count_block_cb,
                      &zcb, NULL));
          }
  
--- 2467,2477 ----
              count_block_cb, &zcb, NULL);
          if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
                  (void) bpobj_iterate_nofree(&spa->spa_dsl_pool->dp_free_bpobj,
                      count_block_cb, &zcb, NULL);
          }
!         if (spa_feature_is_active(spa, SPA_FEATURE_ASYNC_DESTROY)) {
                  VERIFY3U(0, ==, bptree_iterate(spa->spa_meta_objset,
                      spa->spa_dsl_pool->dp_bptree_obj, B_FALSE, count_block_cb,
                      &zcb, NULL));
          }
  
*** 2791,2801 ****
                                  dump_bpobj(&spa->spa_dsl_pool->dp_free_bpobj,
                                      "Pool snapshot frees", 0);
                          }
  
                          if (spa_feature_is_active(spa,
!                             &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
                                  dump_bptree(spa->spa_meta_objset,
                                      spa->spa_dsl_pool->dp_bptree_obj,
                                      "Pool dataset frees");
                          }
                          dump_dtl(spa->spa_root_vdev, 0);
--- 2793,2803 ----
                                  dump_bpobj(&spa->spa_dsl_pool->dp_free_bpobj,
                                      "Pool snapshot frees", 0);
                          }
  
                          if (spa_feature_is_active(spa,
!                             SPA_FEATURE_ASYNC_DESTROY)) {
                                  dump_bptree(spa->spa_meta_objset,
                                      spa->spa_dsl_pool->dp_bptree_obj,
                                      "Pool dataset frees");
                          }
                          dump_dtl(spa->spa_root_vdev, 0);