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>

*** 1832,1843 ****
  static int
  zfs_mvdev_dump_feature_check(void *arg, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
!         if (spa_feature_is_active(spa,
!             &spa_feature_table[SPA_FEATURE_MULTI_VDEV_CRASH_DUMP]))
                  return (1);
          return (0);
  }
  
  /*ARGSUSED*/
--- 1832,1842 ----
  static int
  zfs_mvdev_dump_feature_check(void *arg, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
!         if (spa_feature_is_active(spa, SPA_FEATURE_MULTI_VDEV_CRASH_DUMP))
                  return (1);
          return (0);
  }
  
  /*ARGSUSED*/
*** 1844,1855 ****
  static void
  zfs_mvdev_dump_activate_feature_sync(void *arg, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
!         spa_feature_incr(spa,
!             &spa_feature_table[SPA_FEATURE_MULTI_VDEV_CRASH_DUMP], tx);
  }
  
  static int
  zvol_dump_init(zvol_state_t *zv, boolean_t resize)
  {
--- 1843,1853 ----
  static void
  zfs_mvdev_dump_activate_feature_sync(void *arg, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
!         spa_feature_incr(spa, SPA_FEATURE_MULTI_VDEV_CRASH_DUMP, tx);
  }
  
  static int
  zvol_dump_init(zvol_state_t *zv, boolean_t resize)
  {
*** 1880,1890 ****
           *   Now have spa_root_vdev->vdev_children == 1 (the raidz vdev),
           *   the raidz vdev itself has 3 children.
           */
          if (vd->vdev_children > 1 || vd->vdev_ops == &vdev_raidz_ops) {
                  if (!spa_feature_is_enabled(spa,
!                     &spa_feature_table[SPA_FEATURE_MULTI_VDEV_CRASH_DUMP]))
                          return (SET_ERROR(ENOTSUP));
                  (void) dsl_sync_task(spa_name(spa),
                      zfs_mvdev_dump_feature_check,
                      zfs_mvdev_dump_activate_feature_sync, NULL, 2);
          }
--- 1878,1888 ----
           *   Now have spa_root_vdev->vdev_children == 1 (the raidz vdev),
           *   the raidz vdev itself has 3 children.
           */
          if (vd->vdev_children > 1 || vd->vdev_ops == &vdev_raidz_ops) {
                  if (!spa_feature_is_enabled(spa,
!                     SPA_FEATURE_MULTI_VDEV_CRASH_DUMP))
                          return (SET_ERROR(ENOTSUP));
                  (void) dsl_sync_task(spa_name(spa),
                      zfs_mvdev_dump_feature_check,
                      zfs_mvdev_dump_activate_feature_sync, NULL, 2);
          }
*** 1901,1912 ****
          /*
           * If MULTI_VDEV_CRASH_DUMP is active, use the NOPARITY checksum
           * function.  Otherwise, use the old default -- OFF.
           */
          checksum = spa_feature_is_active(spa,
!             &spa_feature_table[SPA_FEATURE_MULTI_VDEV_CRASH_DUMP]) ?
!             ZIO_CHECKSUM_NOPARITY : ZIO_CHECKSUM_OFF;
  
          /*
           * If we are resizing the dump device then we only need to
           * update the refreservation to match the newly updated
           * zvolsize. Otherwise, we save off the original state of the
--- 1899,1910 ----
          /*
           * If MULTI_VDEV_CRASH_DUMP is active, use the NOPARITY checksum
           * function.  Otherwise, use the old default -- OFF.
           */
          checksum = spa_feature_is_active(spa,
!             SPA_FEATURE_MULTI_VDEV_CRASH_DUMP) ? ZIO_CHECKSUM_NOPARITY :
!             ZIO_CHECKSUM_OFF;
  
          /*
           * If we are resizing the dump device then we only need to
           * update the refreservation to match the newly updated
           * zvolsize. Otherwise, we save off the original state of the