rbd: assign watch request more directly

Both rbd_req_sync_op() and rbd_do_request() have a "linger"
parameter, which is the address of a pointer that should refer to
the osd request structure used to issue a request to an osd.

Only one case ever supplies a non-null "linger" argument: an
CEPH_OSD_OP_WATCH start.  And in that one case it is assigned
&rbd_dev->watch_request.

Within rbd_do_request() (where the assignment ultimately gets made)
we know the rbd_dev and therefore its watch_request field.  We
also know whether the op being sent is CEPH_OSD_OP_WATCH start.

Stop opaquely passing down the "linger" pointer, and instead just
assign the value directly inside rbd_do_request() when it's needed.

This makes it unnecessary for rbd_req_sync_watch() to make
arrangements to hold a value that's not available until a
bit later.  This more clearly separates setting up a watch
request from submitting it.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -1158,7 +1158,6 @@ static int rbd_do_request(struct request *rq,
 			  int coll_index,
 			  void (*rbd_cb)(struct ceph_osd_request *,
 					 struct ceph_msg *),
-			  struct ceph_osd_request **linger_req,
 			  u64 *ver)
 {
 	struct ceph_osd_client *osdc;
@@ -1210,9 +1209,9 @@ static int rbd_do_request(struct request *rq,
 	ceph_osdc_build_request(osd_req, ofs, len, 1, op,
 				snapc, snapid, &mtime);
 
-	if (linger_req) {
+	if (op->op == CEPH_OSD_OP_WATCH && op->watch.flag) {
 		ceph_osdc_set_request_linger(osdc, osd_req);
-		*linger_req = osd_req;
+		rbd_dev->watch_request = osd_req;
 	}
 
 	ret = ceph_osdc_start_request(osdc, osd_req, false);
@@ -1296,7 +1295,6 @@ static int rbd_req_sync_op(struct rbd_device *rbd_dev,
 			   const char *object_name,
 			   u64 ofs, u64 inbound_size,
 			   char *inbound,
-			   struct ceph_osd_request **linger_req,
 			   u64 *ver)
 {
 	int ret;
@@ -1317,7 +1315,7 @@ static int rbd_req_sync_op(struct rbd_device *rbd_dev,
 			  op,
 			  NULL, 0,
 			  NULL,
-			  linger_req, ver);
+			  ver);
 	if (ret < 0)
 		goto done;
 
@@ -1383,7 +1381,7 @@ static int rbd_do_op(struct request *rq,
 			     flags,
 			     op,
 			     coll, coll_index,
-			     rbd_req_cb, 0, NULL);
+			     rbd_req_cb, NULL);
 	if (ret < 0)
 		rbd_coll_end_req_index(rq, coll, coll_index,
 					(s32)ret, seg_len);
@@ -1410,7 +1408,7 @@ static int rbd_req_sync_read(struct rbd_device *rbd_dev,
 		return -ENOMEM;
 
 	ret = rbd_req_sync_op(rbd_dev, CEPH_OSD_FLAG_READ,
-			       op, object_name, ofs, len, buf, NULL, ver);
+			       op, object_name, ofs, len, buf, ver);
 	rbd_osd_req_op_destroy(op);
 
 	return ret;
@@ -1436,7 +1434,7 @@ static int rbd_req_sync_notify_ack(struct rbd_device *rbd_dev,
 			  CEPH_OSD_FLAG_READ,
 			  op,
 			  NULL, 0,
-			  rbd_simple_req_cb, 0, NULL);
+			  rbd_simple_req_cb, NULL);
 
 	rbd_osd_req_op_destroy(op);
 
@@ -1469,7 +1467,6 @@ static void rbd_watch_cb(u64 ver, u64 notify_id, u8 opcode, void *data)
  */
 static int rbd_req_sync_watch(struct rbd_device *rbd_dev, int start)
 {
-	struct ceph_osd_request **linger_req = NULL;
 	struct ceph_osd_req_op *op;
 	int ret = 0;
 
@@ -1481,7 +1478,6 @@ static int rbd_req_sync_watch(struct rbd_device *rbd_dev, int start)
 						&rbd_dev->watch_event);
 		if (ret < 0)
 			return ret;
-		linger_req = &rbd_dev->watch_request;
 	} else {
 		rbd_assert(rbd_dev->watch_request != NULL);
 	}
@@ -1493,7 +1489,7 @@ static int rbd_req_sync_watch(struct rbd_device *rbd_dev, int start)
 		ret = rbd_req_sync_op(rbd_dev,
 			      CEPH_OSD_FLAG_WRITE | CEPH_OSD_FLAG_ONDISK,
 			      op, rbd_dev->header_name,
-			      0, 0, NULL, linger_req, NULL);
+			      0, 0, NULL, NULL);
 
 	/* Cancel the event if we're tearing down, or on error */
 
@@ -1537,7 +1533,7 @@ static int rbd_req_sync_exec(struct rbd_device *rbd_dev,
 
 	ret = rbd_req_sync_op(rbd_dev, CEPH_OSD_FLAG_READ, op,
 			       object_name, 0, inbound_size, inbound,
-			       NULL, ver);
+			       ver);
 
 	rbd_osd_req_op_destroy(op);