mzap_create_impl: use zap_lock_by_dnode()

The only reason this used zap_lock_impl() directly was to avoid an extra
dbuf hold, but there's no real reason to do that. Just use
zap_lock_by_dnode(), and then zap_lock_impl() can be de-exported.

Sponsored-by: TrueNAS
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@truenas.com>
Closes #18546

include/sys/zap_impl.h

@@ -255,10 +255,6 @@ int zap_lock_by_dnode(dnode_t *dn, dmu_tx_t *tx,
     krw_t lti, boolean_t fatreader, boolean_t adding, const void *tag,
     zap_t **zapp);
 
-/* Underlying implementation for above; do not use. */
-int zap_lock_impl(dnode_t *dn, dmu_buf_t *db, const void *tag, dmu_tx_t *tx,
-    krw_t lti, boolean_t fatreader, boolean_t adding, zap_t **zapp);
-
 /* Unlock and release a zap_t. */
 void zap_unlock(zap_t *zap, const void *tag);
 

module/zfs/zap_impl.c

@@ -289,7 +289,7 @@ zap_hash(zap_name_t *zn)
  * This routine "consumes" the caller's hold on the dbuf, which must
  * have the specified tag.
  */
-int
+static int
 zap_lock_impl(dnode_t *dn, dmu_buf_t *db, const void *tag, dmu_tx_t *tx,
     krw_t lti, boolean_t fatreader, boolean_t adding, zap_t **zapp)
 {

module/zfs/zap_micro.c

@@ -405,14 +405,13 @@ mzap_create_impl(dnode_t *dn, int normflags, zap_flags_t flags, dmu_tx_t *tx)
 	if (flags != 0) {
 		zap_t *zap;
 		/* Only fat zap supports flags; upgrade immediately. */
-		VERIFY(dnode_add_ref(dn, FTAG));
-		VERIFY0(zap_lock_impl(dn, db, FTAG, tx, RW_WRITER,
-		    B_FALSE, B_FALSE, &zap));
+		VERIFY0(zap_lock_by_dnode(dn, tx,
+		    RW_WRITER, B_FALSE, B_FALSE, FTAG, &zap));
 		VERIFY0(mzap_upgrade(&zap, FTAG, tx, flags));
 		zap_unlock(zap, FTAG);
-	} else {
-		dmu_buf_rele(db, FTAG);
 	}
+
+	dmu_buf_rele(db, FTAG);
 }
 
 /*