pybind/rados/rados: do not pass prval from stack

The prval is a pointer to an int to write the final completion code of
the rados op.  This can't be on the stack since we immediately leave the
current scope after preparing the op (looong before we do the rados op).

We keep the tuple return value to avoid breaking users of this API
(devicehealth module, gnocchi at a minimum).

Fixes: http://tracker.ceph.com/issues/25175
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 8e36f18)

src/pybind/rados/rados.pyx

@@ -3511,14 +3511,13 @@ returned %d, but should return zero on success." % (self.name, ret))
             ReadOp _read_op = read_op
             rados_omap_iter_t iter_addr = NULL
             int _max_return = max_return
-            int prval = 0
 
         with nogil:
             rados_read_op_omap_get_vals2(_read_op.read_op, _start_after, _filter_prefix,
-                                         _max_return, &iter_addr, NULL, &prval)
+                                         _max_return, &iter_addr, NULL, NULL)
         it = OmapIterator(self)
         it.ctx = iter_addr
-        return it, int(prval)
+        return it, 0   # 0 is meaningless; there for backward-compat
 
     @requires(('read_op', ReadOp), ('start_after', str_type), ('max_return', int))
     def get_omap_keys(self, read_op, start_after, max_return):
@@ -3538,14 +3537,13 @@ returned %d, but should return zero on success." % (self.name, ret))
             ReadOp _read_op = read_op
             rados_omap_iter_t iter_addr = NULL
             int _max_return = max_return
-            int prval = 0
 
         with nogil:
             rados_read_op_omap_get_keys2(_read_op.read_op, _start_after,
-                                         _max_return, &iter_addr, NULL, &prval)
+                                         _max_return, &iter_addr, NULL, NULL)
         it = OmapIterator(self)
         it.ctx = iter_addr
-        return it, int(prval)
+        return it, 0   # 0 is meaningless; there for backward-compat
 
     @requires(('read_op', ReadOp), ('keys', tuple))
     def get_omap_vals_by_keys(self, read_op, keys):
@@ -3563,16 +3561,15 @@ returned %d, but should return zero on success." % (self.name, ret))
             rados_omap_iter_t iter_addr
             char **_keys = to_bytes_array(keys)
             size_t key_num = len(keys)
-            int prval = 0
 
         try:
             with nogil:
                 rados_read_op_omap_get_vals_by_keys(_read_op.read_op,
                                                     <const char**>_keys,
-                                                    key_num, &iter_addr,  &prval)
+                                                    key_num, &iter_addr, NULL)
             it = OmapIterator(self)
             it.ctx = iter_addr
-            return it, int(prval)
+            return it, 0   # 0 is meaningless; there for backward-compat
         finally:
             free(_keys)