3752 want more verifiable dbuf user eviction
Submitted by:   Justin Gibbs <justing@spectralogic.com>
Submitted by:   Will Andrews <willa@spectralogic.com>

*** 72,86 ****
          uint64_t dd_used_breakdown[DD_USED_NUM];
          uint64_t dd_clones; /* dsl_dir objects */
          uint64_t dd_pad[13]; /* pad out to 256 bytes for good measure */
  } dsl_dir_phys_t;
  
  struct dsl_dir {
          /* These are immutable; no lock needed: */
          uint64_t dd_object;
!         dsl_dir_phys_t *dd_phys;
!         dmu_buf_t *dd_dbuf;
          dsl_pool_t *dd_pool;
  
          /* protected by lock on pool's dp_dirty_dirs list */
          txg_node_t dd_dirty_link;
  
--- 72,95 ----
          uint64_t dd_used_breakdown[DD_USED_NUM];
          uint64_t dd_clones; /* dsl_dir objects */
          uint64_t dd_pad[13]; /* pad out to 256 bytes for good measure */
  } dsl_dir_phys_t;
  
+ typedef struct dsl_dir_dbuf {
+         uint8_t dddb_pad[offsetof(dmu_buf_t, db_data)];
+         dsl_dir_phys_t *dddb_data;
+ } dsl_dir_dbuf_t;
+ 
  struct dsl_dir {
+         dmu_buf_user_t db_evict;
+ 
          /* These are immutable; no lock needed: */
          uint64_t dd_object;
!         union {
!                 dmu_buf_t *dd_dmu_db;
!                 dsl_dir_dbuf_t *dd_db;
!         } dd_db_u;
          dsl_pool_t *dd_pool;
  
          /* protected by lock on pool's dp_dirty_dirs list */
          txg_node_t dd_dirty_link;
  
*** 100,109 ****
--- 109,122 ----
  
          /* protected by dd_lock; keep at end of struct for better locality */
          char dd_myname[MAXNAMELEN];
  };
  
+ /* See sys/dmu.h:dmu_buf_user_t for why we have these. */
+ #define dd_dbuf dd_db_u.dd_dmu_db
+ #define dd_phys dd_db_u.dd_db->dddb_data
+ 
  void dsl_dir_rele(dsl_dir_t *dd, void *tag);
  int dsl_dir_hold(dsl_pool_t *dp, const char *name, void *tag,
      dsl_dir_t **, const char **tail);
  int dsl_dir_hold_obj(dsl_pool_t *dp, uint64_t ddobj,
      const char *tail, void *tag, dsl_dir_t **);