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>

*** 2298,2315 ****
                  }
  
                  enabled_feat = fnvlist_alloc();
                  unsup_feat = fnvlist_alloc();
  
!                 if (!feature_is_supported(spa->spa_meta_objset,
!                     spa->spa_feat_for_read_obj, spa->spa_feat_desc_obj,
                      unsup_feat, enabled_feat))
                          missing_feat_read = B_TRUE;
  
                  if (spa_writeable(spa) || state == SPA_LOAD_TRYIMPORT) {
!                         if (!feature_is_supported(spa->spa_meta_objset,
!                             spa->spa_feat_for_write_obj, spa->spa_feat_desc_obj,
                              unsup_feat, enabled_feat)) {
                                  missing_feat_write = B_TRUE;
                          }
                  }
  
--- 2298,2313 ----
                  }
  
                  enabled_feat = fnvlist_alloc();
                  unsup_feat = fnvlist_alloc();
  
!                 if (!spa_features_check(spa, B_FALSE,
                      unsup_feat, enabled_feat))
                          missing_feat_read = B_TRUE;
  
                  if (spa_writeable(spa) || state == SPA_LOAD_TRYIMPORT) {
!                         if (!spa_features_check(spa, B_TRUE,
                              unsup_feat, enabled_feat)) {
                                  missing_feat_write = B_TRUE;
                          }
                  }
  
*** 5912,5934 ****
                  uint64_t intval;
                  char *strval, *fname;
                  zpool_prop_t prop;
                  const char *propname;
                  zprop_type_t proptype;
!                 zfeature_info_t *feature;
  
                  switch (prop = zpool_name_to_prop(nvpair_name(elem))) {
                  case ZPROP_INVAL:
                          /*
                           * We checked this earlier in spa_prop_validate().
                           */
                          ASSERT(zpool_prop_feature(nvpair_name(elem)));
  
                          fname = strchr(nvpair_name(elem), '@') + 1;
!                         VERIFY0(zfeature_lookup_name(fname, &feature));
  
!                         spa_feature_enable(spa, feature, tx);
                          spa_history_log_internal(spa, "set", tx,
                              "%s=enabled", nvpair_name(elem));
                          break;
  
                  case ZPOOL_PROP_VERSION:
--- 5910,5932 ----
                  uint64_t intval;
                  char *strval, *fname;
                  zpool_prop_t prop;
                  const char *propname;
                  zprop_type_t proptype;
!                 spa_feature_t fid;
  
                  switch (prop = zpool_name_to_prop(nvpair_name(elem))) {
                  case ZPROP_INVAL:
                          /*
                           * We checked this earlier in spa_prop_validate().
                           */
                          ASSERT(zpool_prop_feature(nvpair_name(elem)));
  
                          fname = strchr(nvpair_name(elem), '@') + 1;
!                         VERIFY0(zfeature_lookup_name(fname, &fid));
  
!                         spa_feature_enable(spa, fid, tx);
                          spa_history_log_internal(spa, "set", tx,
                              "%s=enabled", nvpair_name(elem));
                          break;
  
                  case ZPOOL_PROP_VERSION: