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>

*** 36,74 ****
  extern "C" {
  #endif
  
  struct zfeature_info;
  
  typedef struct zfeature_info {
          const char *fi_uname;   /* User-facing feature name */
          const char *fi_guid;    /* On-disk feature identifier */
          const char *fi_desc;    /* Feature description */
          boolean_t fi_can_readonly; /* Can open pool readonly w/o support? */
          boolean_t fi_mos;       /* Is the feature necessary to read the MOS? */
!         struct zfeature_info **fi_depends; /* array; null terminated */
  } zfeature_info_t;
  
  typedef int (zfeature_func_t)(zfeature_info_t *fi, void *arg);
  
  #define ZFS_FEATURE_DEBUG
  
- enum spa_feature {
-         SPA_FEATURE_ASYNC_DESTROY,
-         SPA_FEATURE_EMPTY_BPOBJ,
-         SPA_FEATURE_LZ4_COMPRESS,
-         SPA_FEATURE_MULTI_VDEV_CRASH_DUMP,
-         SPA_FEATURE_SPACEMAP_HISTOGRAM,
-         SPA_FEATURES
- } spa_feature_t;
- 
  extern zfeature_info_t spa_feature_table[SPA_FEATURES];
  
  extern boolean_t zfeature_is_valid_guid(const char *);
  
  extern boolean_t zfeature_is_supported(const char *);
! extern int zfeature_lookup_guid(const char *, zfeature_info_t **res);
! extern int zfeature_lookup_name(const char *, zfeature_info_t **res);
  
  extern void zpool_feature_init(void);
  
  #ifdef  __cplusplus
  }
--- 36,77 ----
  extern "C" {
  #endif
  
  struct zfeature_info;
  
+ typedef enum spa_feature {
+         SPA_FEATURE_NONE = -1,
+         SPA_FEATURE_ASYNC_DESTROY,
+         SPA_FEATURE_EMPTY_BPOBJ,
+         SPA_FEATURE_LZ4_COMPRESS,
+         SPA_FEATURE_MULTI_VDEV_CRASH_DUMP,
+         SPA_FEATURE_SPACEMAP_HISTOGRAM,
+         SPA_FEATURE_EXTENSIBLE_DATASET,
+         SPA_FEATURES
+ } spa_feature_t;
+ 
  typedef struct zfeature_info {
+         spa_feature_t fi_feature;
          const char *fi_uname;   /* User-facing feature name */
          const char *fi_guid;    /* On-disk feature identifier */
          const char *fi_desc;    /* Feature description */
          boolean_t fi_can_readonly; /* Can open pool readonly w/o support? */
          boolean_t fi_mos;       /* Is the feature necessary to read the MOS? */
!         /* array of dependencies, terminated by SPA_FEATURE_NONE */
!         const spa_feature_t *fi_depends;
  } zfeature_info_t;
  
  typedef int (zfeature_func_t)(zfeature_info_t *fi, void *arg);
  
  #define ZFS_FEATURE_DEBUG
  
  extern zfeature_info_t spa_feature_table[SPA_FEATURES];
  
  extern boolean_t zfeature_is_valid_guid(const char *);
  
  extern boolean_t zfeature_is_supported(const char *);
! extern int zfeature_lookup_name(const char *name, spa_feature_t *res);
  
  extern void zpool_feature_init(void);
  
  #ifdef  __cplusplus
  }