doc: add missing functions

doc/chapters/mpi-support.texi

@@ -1,3 +1,5 @@
+@c -*-texinfo-*-
+
 @c This file is part of the StarPU Handbook.
 @c Copyright (C) 2009--2011  Universit@'e de Bordeaux 1
 @c Copyright (C) 2010, 2011  Centre National de la Recherche Scientifique
@@ -206,6 +208,14 @@ data. All MPI nodes then process the whole task graph, and StarPU automatically
 determines which node actually execute which task, as well as the required MPI
 transfers.
 
+@deftypefun int starpu_data_set_tag (starpu_data_handle @var{handle}, int @var{tag})
+Tell StarPU-MPI which MPI tag to use when exchanging the data.
+@end deftypefun
+
+@deftypefun int starpu_data_get_tag(starpu_data_handle @var{handle})
+Returns the MPI tag to be used when exchanging the data.
+@end deftypefun
+
 @deftypefun int starpu_data_set_rank (starpu_data_handle @var{handle}, int @var{mpi_rank})
 Tell StarPU-MPI which MPI node "owns" a given data, that is, the node which will
 always keep an up-to-date value, and will by default execute tasks which write
@@ -250,10 +260,9 @@ data twice to the same MPI node, unless the data has been modified.
 @end deftypefun
 
 @deftypefun void starpu_mpi_get_data_on_node (MPI_Comm @var{comm}, starpu_data_handle @var{data_handle}, int @var{node})
+todo
 @end deftypefun
 
-@page
-
 Here an stencil example showing how to use @code{starpu_mpi_insert_task}. One
 first needs to define a distribution function which specifies the
 locality of the data. Note that that distribution information needs to