rbd: pass flags to rbd_req_sync_exec()

In order to allow both read requests and write requests to be
initiated using rbd_req_sync_exec(), add an OSD flags value
which can be passed down to rbd_req_sync_op().  Rename the "data"
and "len" parameters to be more clear that they represent data
that is outbound.

At this point, this function is still only used (and only works) for
write requests.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -1437,23 +1437,33 @@ fail:
 }
 
 /*
- * Request sync osd read
+ * Synchronous osd object method call
  */
 static int rbd_req_sync_exec(struct rbd_device *rbd_dev,
 			     const char *object_name,
 			     const char *class_name,
 			     const char *method_name,
-			     const char *data,
-			     int len,
+			     const char *outbound,
+			     size_t outbound_size,
+			     int flags,
 			     u64 *ver)
 {
 	struct ceph_osd_req_op *ops;
 	int class_name_len = strlen(class_name);
 	int method_name_len = strlen(method_name);
+	int payload_size;
 	int ret;
 
-	ops = rbd_create_rw_ops(1, CEPH_OSD_OP_CALL,
-				    class_name_len + method_name_len + len);
+	/*
+	 * Any input parameters required by the method we're calling
+	 * will be sent along with the class and method names as
+	 * part of the message payload.  That data and its size are
+	 * supplied via the indata and indata_len fields (named from
+	 * the perspective of the server side) in the OSD request
+	 * operation.
+	 */
+	payload_size = class_name_len + method_name_len + outbound_size;
+	ops = rbd_create_rw_ops(1, CEPH_OSD_OP_CALL, payload_size);
 	if (!ops)
 		return -ENOMEM;
 
@@ -1462,13 +1472,12 @@ static int rbd_req_sync_exec(struct rbd_device *rbd_dev,
 	ops[0].cls.method_name = method_name;
 	ops[0].cls.method_len = (__u8) method_name_len;
 	ops[0].cls.argc = 0;
-	ops[0].cls.indata = data;
-	ops[0].cls.indata_len = len;
+	ops[0].cls.indata = outbound;
+	ops[0].cls.indata_len = outbound_size;
 
 	ret = rbd_req_sync_op(rbd_dev, NULL,
 			       CEPH_NOSNAP,
-			       CEPH_OSD_FLAG_WRITE | CEPH_OSD_FLAG_ONDISK,
-			       ops,
+			       flags, ops,
 			       object_name, 0, 0, NULL, NULL, ver);
 
 	rbd_destroy_ops(ops);
@@ -1780,7 +1789,9 @@ static int rbd_header_add_snap(struct rbd_device *rbd_dev,
 
 	ret = rbd_req_sync_exec(rbd_dev, rbd_dev->header_name,
 				"rbd", "snap_add",
-				data, p - data, NULL);
+				data, (size_t) (p - data),
+				CEPH_OSD_FLAG_WRITE | CEPH_OSD_FLAG_ONDISK,
+				NULL);
 
 	kfree(data);