drbd: fix effective error returned when refusing an invalidate

Since commit
  drbd: Disallow the peer_disk_state to be D_OUTDATED while connected
trying to invalidate a disconnected Primary returned an error code
that did not really match the situation:
"Refusing to be Outdated while Connected"

Insert two more specific conditions into is_valid_state(),
changing that to "Need access to UpToDate data",
respectively "Need a connection to start verify or resync".
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_state.c

@@ -570,6 +570,13 @@ is_valid_state(struct drbd_conf *mdev, union drbd_state ns)
 		  mdev->tconn->agreed_pro_version < 88)
 		rv = SS_NOT_SUPPORTED;
 
+	else if (ns.role == R_PRIMARY && ns.disk < D_UP_TO_DATE && ns.pdsk < D_UP_TO_DATE)
+		rv = SS_NO_UP_TO_DATE_DISK;
+
+	else if ((ns.conn == C_STARTING_SYNC_S || ns.conn == C_STARTING_SYNC_T) &&
+                 ns.pdsk == D_UNKNOWN)
+		rv = SS_NEED_CONNECTION;
+
 	else if (ns.conn >= C_CONNECTED && ns.pdsk == D_UNKNOWN)
 		rv = SS_CONNECTED_OUTDATES;