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

@@ -125,10 +125,15 @@
          */
 
         uint16_t l_hash[1];
 } zap_leaf_phys_t;
 
+typedef struct zap_leaf_dbuf {
+        uint8_t zldb_pad[offsetof(dmu_buf_t, db_data)];
+        zap_leaf_phys_t *zldb_data;
+} zap_leaf_dbuf_t;
+
 typedef union zap_leaf_chunk {
         struct zap_leaf_entry {
                 uint8_t le_type;                /* always ZAP_CHUNK_ENTRY */
                 uint8_t le_value_intlen;        /* size of value's ints */
                 uint16_t le_next;               /* next entry in hash chain */

@@ -150,17 +155,22 @@
                 uint16_t lf_next;       /* next in free list, or CHAIN_END */
         } l_free;
 } zap_leaf_chunk_t;
 
 typedef struct zap_leaf {
+        dmu_buf_user_t db_evict;
         krwlock_t l_rwlock;
         uint64_t l_blkid;               /* 1<<ZAP_BLOCK_SHIFT byte block off */
         int l_bs;                       /* block size shift */
-        dmu_buf_t *l_dbuf;
-        zap_leaf_phys_t *l_phys;
+        union {
+                dmu_buf_t *l_dmu_db;
+                zap_leaf_dbuf_t *l_db;
+        } zl_db_u;
 } zap_leaf_t;
 
+#define l_dbuf zl_db_u.l_dmu_db
+#define l_phys zl_db_u.l_db->zldb_data
 
 typedef struct zap_entry_handle {
         /* below is set by zap_leaf.c and is public to zap.c */
         uint64_t zeh_num_integers;
         uint64_t zeh_hash;