field_info_instances function to retrieve all fields info under a content type.
As from API page,
$entity_typeis not set, return all instances keyed by entity type and bundle name.
$entity_typeis set, return all instances for that entity type, keyed by bundle name.
$bundle_nameare set, return all instances for that bundle.
I didn't get the third point here. what is the default order for return output by