rbd: define inbound data size for method ops

When rbd creates an object request containing an object method call
operation it is passing 0 for the size.  I originally thought this
was because the length was not needed for method calls, but I think
it really should be supplied, to describe how much space is
available to receive response data.  So provide the supplied length.

This resolves:
    http://tracker.ceph.com/issues/4659

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

drivers/block/rbd.c

@@ -1840,12 +1840,11 @@ static int rbd_obj_method_sync(struct rbd_device *rbd_dev,
 	int ret;
 
 	/*
-	 * Method calls are ultimately read operations but they
+	 * Method calls are ultimately read operations.  The result
-	 * don't involve object data (so no offset or length).
+	 * should placed into the inbound buffer provided.  They
-	 * The result should placed into the inbound buffer
+	 * also supply outbound data--parameters for the object
-	 * provided.  They also supply outbound data--parameters for
+	 * method.  Currently if this is present it will be a
-	 * the object method.  Currently if this is present it will
+	 * snapshot id.
-	 * be a snapshot id.
 	 */
 	page_count = (u32) calc_pages_for(0, inbound_size);
 	pages = ceph_alloc_page_vector(page_count, GFP_KERNEL);
@@ -1853,7 +1852,7 @@ static int rbd_obj_method_sync(struct rbd_device *rbd_dev,
 		return PTR_ERR(pages);
 
 	ret = -ENOMEM;
-	obj_request = rbd_obj_request_create(object_name, 0, 0,
+	obj_request = rbd_obj_request_create(object_name, 0, inbound_size,
 							OBJ_REQUEST_PAGES);
 	if (!obj_request)
 		goto out;