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>

*** 47,59 ****
  struct dsl_pool;
  
  #define DS_FLAG_INCONSISTENT    (1ULL<<0)
  #define DS_IS_INCONSISTENT(ds)  \
          ((ds)->ds_phys->ds_flags & DS_FLAG_INCONSISTENT)
  /*
!  * Note: nopromote can not yet be set, but we want support for it in this
!  * on-disk version, so that we don't need to upgrade for it later.
   */
  #define DS_FLAG_NOPROMOTE       (1ULL<<1)
  
  /*
   * DS_FLAG_UNIQUE_ACCURATE is set if ds_unique_bytes has been correctly
--- 47,59 ----
  struct dsl_pool;
  
  #define DS_FLAG_INCONSISTENT    (1ULL<<0)
  #define DS_IS_INCONSISTENT(ds)  \
          ((ds)->ds_phys->ds_flags & DS_FLAG_INCONSISTENT)
+ 
  /*
!  * Do not allow this dataset to be promoted.
   */
  #define DS_FLAG_NOPROMOTE       (1ULL<<1)
  
  /*
   * DS_FLAG_UNIQUE_ACCURATE is set if ds_unique_bytes has been correctly
*** 69,78 ****
--- 69,83 ----
  #define DS_FLAG_DEFER_DESTROY   (1ULL<<3)
  #define DS_IS_DEFER_DESTROY(ds) \
          ((ds)->ds_phys->ds_flags & DS_FLAG_DEFER_DESTROY)
  
  /*
+  * DS_FIELD_* are strings that are used in the "extensified" dataset zap object.
+  * They should be of the format <reverse-dns>:<field>.
+  */
+ 
+ /*
   * DS_FLAG_CI_DATASET is set if the dataset contains a file system whose
   * name lookups should be performed case-insensitively.
   */
  #define DS_FLAG_CI_DATASET      (1ULL<<16)