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>

*** 34,59 ****
   * Return an empty bpobj, preferably the empty dummy one (dp_empty_bpobj).
   */
  uint64_t
  bpobj_alloc_empty(objset_t *os, int blocksize, dmu_tx_t *tx)
  {
-         zfeature_info_t *empty_bpobj_feat =
-             &spa_feature_table[SPA_FEATURE_EMPTY_BPOBJ];
          spa_t *spa = dmu_objset_spa(os);
          dsl_pool_t *dp = dmu_objset_pool(os);
  
!         if (spa_feature_is_enabled(spa, empty_bpobj_feat)) {
!                 if (!spa_feature_is_active(spa, empty_bpobj_feat)) {
                          ASSERT0(dp->dp_empty_bpobj);
                          dp->dp_empty_bpobj =
                              bpobj_alloc(os, SPA_MAXBLOCKSIZE, tx);
                          VERIFY(zap_add(os,
                              DMU_POOL_DIRECTORY_OBJECT,
                              DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                              &dp->dp_empty_bpobj, tx) == 0);
                  }
!                 spa_feature_incr(spa, empty_bpobj_feat, tx);
                  ASSERT(dp->dp_empty_bpobj != 0);
                  return (dp->dp_empty_bpobj);
          } else {
                  return (bpobj_alloc(os, blocksize, tx));
          }
--- 34,57 ----
   * Return an empty bpobj, preferably the empty dummy one (dp_empty_bpobj).
   */
  uint64_t
  bpobj_alloc_empty(objset_t *os, int blocksize, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_objset_spa(os);
          dsl_pool_t *dp = dmu_objset_pool(os);
  
!         if (spa_feature_is_enabled(spa, SPA_FEATURE_EMPTY_BPOBJ)) {
!                 if (!spa_feature_is_active(spa, SPA_FEATURE_EMPTY_BPOBJ)) {
                          ASSERT0(dp->dp_empty_bpobj);
                          dp->dp_empty_bpobj =
                              bpobj_alloc(os, SPA_MAXBLOCKSIZE, tx);
                          VERIFY(zap_add(os,
                              DMU_POOL_DIRECTORY_OBJECT,
                              DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                              &dp->dp_empty_bpobj, tx) == 0);
                  }
!                 spa_feature_incr(spa, SPA_FEATURE_EMPTY_BPOBJ, tx);
                  ASSERT(dp->dp_empty_bpobj != 0);
                  return (dp->dp_empty_bpobj);
          } else {
                  return (bpobj_alloc(os, blocksize, tx));
          }
*** 60,75 ****
  }
  
  void
  bpobj_decr_empty(objset_t *os, dmu_tx_t *tx)
  {
-         zfeature_info_t *empty_bpobj_feat =
-             &spa_feature_table[SPA_FEATURE_EMPTY_BPOBJ];
          dsl_pool_t *dp = dmu_objset_pool(os);
  
!         spa_feature_decr(dmu_objset_spa(os), empty_bpobj_feat, tx);
!         if (!spa_feature_is_active(dmu_objset_spa(os), empty_bpobj_feat)) {
                  VERIFY3U(0, ==, zap_remove(dp->dp_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT,
                      DMU_POOL_EMPTY_BPOBJ, tx));
                  VERIFY3U(0, ==, dmu_object_free(os, dp->dp_empty_bpobj, tx));
                  dp->dp_empty_bpobj = 0;
--- 58,72 ----
  }
  
  void
  bpobj_decr_empty(objset_t *os, dmu_tx_t *tx)
  {
          dsl_pool_t *dp = dmu_objset_pool(os);
  
!         spa_feature_decr(dmu_objset_spa(os), SPA_FEATURE_EMPTY_BPOBJ, tx);
!         if (!spa_feature_is_active(dmu_objset_spa(os),
!             SPA_FEATURE_EMPTY_BPOBJ)) {
                  VERIFY3U(0, ==, zap_remove(dp->dp_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT,
                      DMU_POOL_EMPTY_BPOBJ, tx));
                  VERIFY3U(0, ==, dmu_object_free(os, dp->dp_empty_bpobj, tx));
                  dp->dp_empty_bpobj = 0;
*** 263,272 ****
--- 260,270 ----
          err = dmu_object_info(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs, &doi);
          if (err) {
                  mutex_exit(&bpo->bpo_lock);
                  return (err);
          }
+         ASSERT3U(doi.doi_type, ==, DMU_OT_BPOBJ_SUBOBJ);
          epb = doi.doi_data_block_size / sizeof (uint64_t);
  
          for (i = bpo->bpo_phys->bpo_num_subobjs - 1; i >= 0; i--) {
                  uint64_t *objarray;
                  uint64_t offset, blkoff;