data interfaces: the pack operation of user-defined data interfaces now defines a count parameter which should be set to thesize of the buffer created by the packing of the data

doc/chapters/advanced-api.texi

@@ -72,8 +72,8 @@ todo
 @item @code{struct starpu_multiformat_data_interface_ops* (*get_mf_ops)(void *data_interface)}
 todo
 
-@item @code{int (*pack_data)(starpu_data_handle_t handle, uint32_t node, void **ptr)}
-Pack the data handle into a contiguous buffer at the address @code{ptr}
+@item @code{int (*pack_data)(starpu_data_handle_t handle, uint32_t node, void **ptr, size_t *count)}
+Pack the data handle into a contiguous buffer at the address @code{ptr} and set the size of the newly created buffer in @code{count}
 
 @item @code{int (*unpack_data)(starpu_data_handle_t handle, uint32_t node, void *ptr)}
 Unpack the data handle from the contiguous buffer at the address @code{ptr}

doc/chapters/mpi-support.texi

@@ -259,21 +259,22 @@ of data interface} can also be used within StarPU-MPI and exchanged
 between nodes. Two functions needs to be defined through
 the type @code{struct starpu_data_interface_ops} (@pxref{Data
 Interface API}). The pack function takes a handle and returns a
-contiguous memory buffer where data to be conveyed to another node
+contiguous memory buffer along with its size where data to be conveyed to another node
 should be copied. The reversed operation is implemented in the unpack
 function which takes a contiguous memory buffer and recreates the data
 handle.
 
 @cartouche
 @smallexample
-static int complex_pack_data(starpu_data_handle_t handle, uint32_t node, void **ptr)
+static int complex_pack_data(starpu_data_handle_t handle, uint32_t node, void **ptr, size_t *count)
 @{
   STARPU_ASSERT(starpu_data_test_if_allocated_on_node(handle, node));
 
   struct starpu_complex_interface *complex_interface =
     (struct starpu_complex_interface *) starpu_data_get_interface_on_node(handle, node);
 
-  *ptr = malloc(complex_get_size(handle));
+  *count = complex_get_size(handle);
+  *ptr = malloc(*count);
   memcpy(*ptr, complex_interface->real, complex_interface->nx*sizeof(double));
   memcpy(*ptr+complex_interface->nx*sizeof(double), complex_interface->imaginary,
          complex_interface->nx*sizeof(double));

examples/interface/complex_interface.c

@@ -171,14 +171,15 @@ static void *complex_handle_to_pointer(starpu_data_handle_t handle, uint32_t nod
 	return (void*) complex_interface->real;
 }
 
-static int complex_pack_data(starpu_data_handle_t handle, uint32_t node, void **ptr)
+static int complex_pack_data(starpu_data_handle_t handle, uint32_t node, void **ptr, size_t *count)
 {
 	STARPU_ASSERT(starpu_data_test_if_allocated_on_node(handle, node));
 
 	struct starpu_complex_interface *complex_interface = (struct starpu_complex_interface *)
 		starpu_data_get_interface_on_node(handle, node);
 
-	*ptr = malloc(complex_get_size(handle));
+	*count = complex_get_size(handle);
+	*ptr = malloc(*count);
 	memcpy(*ptr, complex_interface->real, complex_interface->nx*sizeof(double));
 	memcpy(*ptr+complex_interface->nx*sizeof(double), complex_interface->imaginary, complex_interface->nx*sizeof(double));
 

include/starpu_data_interfaces.h

@@ -133,7 +133,7 @@ struct starpu_data_interface_ops
 	struct starpu_multiformat_data_interface_ops* (*get_mf_ops)(void *data_interface);
 
 	/* Pack the data handle into a contiguous buffer at the address ptr and store the size of the buffer in count */
-	int (*pack_data)(starpu_data_handle_t handle, uint32_t node, void **ptr);
+        int (*pack_data)(starpu_data_handle_t handle, uint32_t node, void **ptr, size_t *count);
 	/* Unpack the data handle from the contiguous buffer at the address ptr */
 	int (*unpack_data)(starpu_data_handle_t handle, uint32_t node, void *ptr);
 };

src/datawizard/interfaces/data_interface.c

@@ -684,8 +684,7 @@ int starpu_data_interface_get_next_id(void)
 int starpu_handle_pack_data(starpu_data_handle_t handle, void **ptr, size_t *count)
 {
 	STARPU_ASSERT(handle->ops->pack_data);
-	*count = starpu_handle_get_size(handle);
-	return handle->ops->pack_data(handle, _starpu_get_local_memory_node(), ptr);
+	return handle->ops->pack_data(handle, _starpu_get_local_memory_node(), ptr, count);
 }
 
 int starpu_handle_unpack_data(starpu_data_handle_t handle, void *ptr)