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>

*** 25,34 ****
--- 25,36 ----
  
  #include <sys/dmu.h>
  #include <sys/dmu_objset.h>
  #include <sys/dmu_tx.h>
  #include <sys/dnode.h>
+ #include <sys/zap.h>
+ #include <sys/zfeature.h>
  
  uint64_t
  dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
      dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
  {
*** 192,197 ****
--- 194,250 ----
              (hole ? DNODE_FIND_HOLE : 0), &offset, 0, DNODES_PER_BLOCK, txg);
  
          *objectp = offset >> DNODE_SHIFT;
  
          return (error);
+ }
+ 
+ /*
+  * Turn this object from old_type into DMU_OTN_ZAP_METADATA, and bump the
+  * refcount on SPA_FEATURE_EXTENSIBLE_DATASET.
+  *
+  * Only for use from syncing context, on MOS objects.
+  */
+ void
+ dmu_object_zapify(objset_t *mos, uint64_t object, dmu_object_type_t old_type,
+     dmu_tx_t *tx)
+ {
+         dnode_t *dn;
+ 
+         ASSERT(dmu_tx_is_syncing(tx));
+ 
+         VERIFY0(dnode_hold(mos, object, FTAG, &dn));
+         if (dn->dn_type == DMU_OTN_ZAP_METADATA) {
+                 dnode_rele(dn, FTAG);
+                 return;
+         }
+         ASSERT3U(dn->dn_type, ==, old_type);
+         ASSERT0(dn->dn_maxblkid);
+         dn->dn_next_type[tx->tx_txg & TXG_MASK] = dn->dn_type =
+             DMU_OTN_ZAP_METADATA;
+         dnode_setdirty(dn, tx);
+         dnode_rele(dn, FTAG);
+ 
+         mzap_create_impl(mos, object, 0, 0, tx);
+ 
+         spa_feature_incr(dmu_objset_spa(mos),
+             SPA_FEATURE_EXTENSIBLE_DATASET, tx);
+ }
+ 
+ void
+ dmu_object_free_zapified(objset_t *mos, uint64_t object, dmu_tx_t *tx)
+ {
+         dnode_t *dn;
+         dmu_object_type_t t;
+ 
+         ASSERT(dmu_tx_is_syncing(tx));
+ 
+         VERIFY0(dnode_hold(mos, object, FTAG, &dn));
+         t = dn->dn_type;
+         dnode_rele(dn, FTAG);
+ 
+         if (t == DMU_OTN_ZAP_METADATA) {
+                 spa_feature_decr(dmu_objset_spa(mos),
+                     SPA_FEATURE_EXTENSIBLE_DATASET, tx);
+         }
+         VERIFY0(dmu_object_free(mos, object, tx));
  }