libceph: fix truncate size calculation

check the "not truncated yet" case
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>

net/ceph/osd_client.c

@@ -733,6 +733,7 @@ struct ceph_osd_request *ceph_osdc_new_request(struct ceph_osd_client *osdc,
 
 	object_size = le32_to_cpu(layout->fl_object_size);
 	object_base = off - objoff;
+	if (!(truncate_seq == 1 && truncate_size == -1ULL)) {
 		if (truncate_size <= object_base) {
 			truncate_size = 0;
 		} else {
@@ -740,6 +741,7 @@ struct ceph_osd_request *ceph_osdc_new_request(struct ceph_osd_client *osdc,
 			if (truncate_size > object_size)
 				truncate_size = object_size;
 		}
+	}
 
 	osd_req_op_extent_init(req, 0, opcode, objoff, objlen,
 				truncate_size, truncate_seq);