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>

*** 100,110 ****
           * make sure that the scan_async_destroying flag is initialized
           * appropriately.
           */
          ASSERT(!scn->scn_async_destroying);
          scn->scn_async_destroying = spa_feature_is_active(dp->dp_spa,
!             &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY]);
  
          err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              "scrub_func", sizeof (uint64_t), 1, &f);
          if (err == 0) {
                  /*
--- 100,110 ----
           * make sure that the scan_async_destroying flag is initialized
           * appropriately.
           */
          ASSERT(!scn->scn_async_destroying);
          scn->scn_async_destroying = spa_feature_is_active(dp->dp_spa,
!             SPA_FEATURE_ASYNC_DESTROY);
  
          err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              "scrub_func", sizeof (uint64_t), 1, &f);
          if (err == 0) {
                  /*
*** 1351,1361 ****
  
          if (spa->spa_load_state != SPA_LOAD_NONE)
                  return (B_FALSE);
          if (spa_shutting_down(spa))
                  return (B_FALSE);
- 
          if (scn->scn_phys.scn_state == DSS_SCANNING ||
              scn->scn_async_destroying)
                  return (B_TRUE);
  
          if (spa_version(scn->scn_dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
--- 1351,1360 ----
*** 1410,1420 ****
                  err = bpobj_iterate(&dp->dp_free_bpobj,
                      dsl_scan_free_block_cb, scn, tx);
                  VERIFY3U(0, ==, zio_wait(scn->scn_zio_root));
  
                  if (err == 0 && spa_feature_is_active(spa,
!                     &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
                          ASSERT(scn->scn_async_destroying);
                          scn->scn_is_bptree = B_TRUE;
                          scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
                              NULL, ZIO_FLAG_MUSTSUCCEED);
                          err = bptree_iterate(dp->dp_meta_objset,
--- 1409,1419 ----
                  err = bpobj_iterate(&dp->dp_free_bpobj,
                      dsl_scan_free_block_cb, scn, tx);
                  VERIFY3U(0, ==, zio_wait(scn->scn_zio_root));
  
                  if (err == 0 && spa_feature_is_active(spa,
!                     SPA_FEATURE_ASYNC_DESTROY)) {
                          ASSERT(scn->scn_async_destroying);
                          scn->scn_is_bptree = B_TRUE;
                          scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
                              NULL, ZIO_FLAG_MUSTSUCCEED);
                          err = bptree_iterate(dp->dp_meta_objset,
*** 1421,1435 ****
                              dp->dp_bptree_obj, B_TRUE, dsl_scan_free_block_cb,
                              scn, tx);
                          VERIFY0(zio_wait(scn->scn_zio_root));
  
                          if (err == 0) {
-                                 zfeature_info_t *feat = &spa_feature_table
-                                     [SPA_FEATURE_ASYNC_DESTROY];
                                  /* finished; deactivate async destroy feature */
!                                 spa_feature_decr(spa, feat, tx);
!                                 ASSERT(!spa_feature_is_active(spa, feat));
                                  VERIFY0(zap_remove(dp->dp_meta_objset,
                                      DMU_POOL_DIRECTORY_OBJECT,
                                      DMU_POOL_BPTREE_OBJ, tx));
                                  VERIFY0(bptree_free(dp->dp_meta_objset,
                                      dp->dp_bptree_obj, tx));
--- 1420,1434 ----
                              dp->dp_bptree_obj, B_TRUE, dsl_scan_free_block_cb,
                              scn, tx);
                          VERIFY0(zio_wait(scn->scn_zio_root));
  
                          if (err == 0) {
                                  /* finished; deactivate async destroy feature */
!                                 spa_feature_decr(spa, SPA_FEATURE_ASYNC_DESTROY,
!                                     tx);
!                                 ASSERT(!spa_feature_is_active(spa,
!                                     SPA_FEATURE_ASYNC_DESTROY));
                                  VERIFY0(zap_remove(dp->dp_meta_objset,
                                      DMU_POOL_DIRECTORY_OBJECT,
                                      DMU_POOL_BPTREE_OBJ, tx));
                                  VERIFY0(bptree_free(dp->dp_meta_objset,
                                      dp->dp_bptree_obj, tx));