Perform necessary operations just before fields data get saved.
We take no specific action here, we just give other modules the opportunity to act.
$entity_type: The type of $entity; e.g. 'node' or 'user'.
$entity: The entity with fields to process.
function field_attach_presave($entity_type, $entity) {
_field_invoke('presave', $entity_type, $entity);
// Let other modules act on presaving the entity.
module_invoke_all('field_attach_presave', $entity_type, $entity);
}