void mongoc_bulk_operation_update (mongoc_bulk_operation_t *bulk, const bson_t *selector, const bson_t *document, bool upsert);
This function queues an update as part of a bulk operation. This does not execute the operation. To execute the entirety of the bulk operation call mongoc_bulk_operation_execute().
document MUST only contain fields whose key starts with $. See the update document specification for more details.
Errors are propagated via mongoc_bulk_operation_execute().