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

*** 1297,1309 ****
          return (0);
  }
  
  /*ARGSUSED*/
  void
! sa_evict(dmu_buf_t *db, void *sap)
  {
!         panic("evicting sa dbuf %p\n", (void *)db);
  }
  
  static void
  sa_idx_tab_rele(objset_t *os, void *arg)
  {
--- 1297,1309 ----
          return (0);
  }
  
  /*ARGSUSED*/
  void
! sa_evict(dmu_buf_user_t *dbu)
  {
!         panic("evicting sa dbuf\n");
  }
  
  static void
  sa_idx_tab_rele(objset_t *os, void *arg)
  {
*** 1338,1350 ****
  }
  
  void
  sa_handle_destroy(sa_handle_t *hdl)
  {
          mutex_enter(&hdl->sa_lock);
!         (void) dmu_buf_update_user((dmu_buf_t *)hdl->sa_bonus, hdl,
!             NULL, NULL, NULL);
  
          if (hdl->sa_bonus_tab) {
                  sa_idx_tab_rele(hdl->sa_os, hdl->sa_bonus_tab);
                  hdl->sa_bonus_tab = NULL;
          }
--- 1338,1351 ----
  }
  
  void
  sa_handle_destroy(sa_handle_t *hdl)
  {
+         dmu_buf_t *db = hdl->sa_bonus;
+ 
          mutex_enter(&hdl->sa_lock);
!         (void) dmu_buf_remove_user(db, &hdl->db_evict);
  
          if (hdl->sa_bonus_tab) {
                  sa_idx_tab_rele(hdl->sa_os, hdl->sa_bonus_tab);
                  hdl->sa_bonus_tab = NULL;
          }
*** 1366,1402 ****
  sa_handle_get_from_db(objset_t *os, dmu_buf_t *db, void *userp,
      sa_handle_type_t hdl_type, sa_handle_t **handlepp)
  {
          int error = 0;
          dmu_object_info_t doi;
!         sa_handle_t *handle;
  
  #ifdef ZFS_DEBUG
          dmu_object_info_from_db(db, &doi);
          ASSERT(doi.doi_bonus_type == DMU_OT_SA ||
              doi.doi_bonus_type == DMU_OT_ZNODE);
  #endif
          /* find handle, if it exists */
          /* if one doesn't exist then create a new one, and initialize it */
  
!         handle = (hdl_type == SA_HDL_SHARED) ? dmu_buf_get_user(db) : NULL;
          if (handle == NULL) {
!                 sa_handle_t *newhandle;
                  handle = kmem_cache_alloc(sa_cache, KM_SLEEP);
                  handle->sa_userp = userp;
                  handle->sa_bonus = db;
                  handle->sa_os = os;
                  handle->sa_spill = NULL;
  
                  error = sa_build_index(handle, SA_BONUS);
!                 newhandle = (hdl_type == SA_HDL_SHARED) ?
!                     dmu_buf_set_user_ie(db, handle,
!                     NULL, sa_evict) : NULL;
! 
!                 if (newhandle != NULL) {
                          kmem_cache_free(sa_cache, handle);
!                         handle = newhandle;
                  }
          }
          *handlepp = handle;
  
          return (error);
--- 1367,1408 ----
  sa_handle_get_from_db(objset_t *os, dmu_buf_t *db, void *userp,
      sa_handle_type_t hdl_type, sa_handle_t **handlepp)
  {
          int error = 0;
          dmu_object_info_t doi;
!         sa_handle_t *handle = NULL;
  
  #ifdef ZFS_DEBUG
          dmu_object_info_from_db(db, &doi);
          ASSERT(doi.doi_bonus_type == DMU_OT_SA ||
              doi.doi_bonus_type == DMU_OT_ZNODE);
  #endif
          /* find handle, if it exists */
          /* if one doesn't exist then create a new one, and initialize it */
  
!         if (hdl_type == SA_HDL_SHARED)
!                 handle = (sa_handle_t *)dmu_buf_get_user(db);
! 
          if (handle == NULL) {
!                 sa_handle_t *winner = NULL;
! 
!                 bzero(&handle->db_evict, sizeof(dmu_buf_user_t));
                  handle = kmem_cache_alloc(sa_cache, KM_SLEEP);
                  handle->sa_userp = userp;
                  handle->sa_bonus = db;
                  handle->sa_os = os;
                  handle->sa_spill = NULL;
  
                  error = sa_build_index(handle, SA_BONUS);
!                 if (hdl_type == SA_HDL_SHARED) {
!                         dmu_buf_init_user(&handle->db_evict, sa_evict);
!                         winner = (sa_handle_t *)
!                             dmu_buf_set_user_ie(db, &handle->db_evict);
!                 }
!                 if (winner != NULL) {
                          kmem_cache_free(sa_cache, handle);
!                         handle = winner;
                  }
          }
          *handlepp = handle;
  
          return (error);
*** 1905,1916 ****
  }
  
  void
  sa_update_user(sa_handle_t *newhdl, sa_handle_t *oldhdl)
  {
!         (void) dmu_buf_update_user((dmu_buf_t *)newhdl->sa_bonus,
!             oldhdl, newhdl, NULL, sa_evict);
          oldhdl->sa_bonus = NULL;
  }
  
  void
  sa_set_userp(sa_handle_t *hdl, void *ptr)
--- 1911,1926 ----
  }
  
  void
  sa_update_user(sa_handle_t *newhdl, sa_handle_t *oldhdl)
  {
!         dmu_buf_user_t *new_user = &newhdl->db_evict;
!         dmu_buf_user_t *old_user = &oldhdl->db_evict;
! 
!         dmu_buf_init_user(new_user, sa_evict);
!         VERIFY(dmu_buf_replace_user(newhdl->sa_bonus, old_user,
!             new_user) == old_user);
          oldhdl->sa_bonus = NULL;
  }
  
  void
  sa_set_userp(sa_handle_t *hdl, void *ptr)