rbd: don't assign extent info in rbd_do_request()

In rbd_do_request() there's a sort of last-minute assignment of the
extent offset and length and payload length for read and write
operations.  Move those assignments into the caller (in those spots
that might initiate read or write operations)
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -1156,13 +1156,6 @@ static int rbd_do_request(struct request *rq,
 	osd_req->r_oid_len = strlen(osd_req->r_oid);
 
 	osd_req->r_file_layout = rbd_dev->layout;	/* struct */
-
-	if (op->op == CEPH_OSD_OP_READ || op->op == CEPH_OSD_OP_WRITE) {
-		op->extent.offset = ofs;
-		op->extent.length = len;
-		if (op->op == CEPH_OSD_OP_WRITE)
-			op->payload_len = len;
-	}
 	osd_req->r_num_pages = calc_pages_for(ofs, len);
 	osd_req->r_page_alignment = ofs & ~PAGE_MASK;
 
@@ -1269,6 +1262,13 @@ static int rbd_req_sync_op(struct rbd_device *rbd_dev,
 	if (IS_ERR(pages))
 		return PTR_ERR(pages);
 
+	if (op->op == CEPH_OSD_OP_READ || op->op == CEPH_OSD_OP_WRITE) {
+		op->extent.offset = ofs;
+		op->extent.length = inbound_size;
+		if (op->op == CEPH_OSD_OP_WRITE)
+			op->payload_len = inbound_size;
+	}
+
 	ret = rbd_do_request(NULL, rbd_dev, NULL, CEPH_NOSNAP,
 			  object_name, ofs, inbound_size, NULL,
 			  pages, num_pages,
@@ -1332,6 +1332,9 @@ static int rbd_do_op(struct request *rq,
 	op = rbd_create_rw_op(opcode, payload_len);
 	if (!op)
 		goto done;
+	op->extent.offset = seg_ofs;
+	op->extent.length = seg_len;
+	op->payload_len = payload_len;
 
 	/* we've taken care of segment sizes earlier when we
 	   cloned the bios. We should never have a segment