/* Populate front untouched region of new data cluster  */
static void qed_aio_write_prefill(void *opaque, int ret)
/* Populate front untouched region of new data cluster  */
static void qed_aio_write_prefill(void *opaque, int ret)
{
    QEDAIOCB *acb = opaque;
    BDRVQEDState *s = acb_to_s(acb);
    uint64_t start = qed_start_of_cluster(s, acb->cur_pos);
    uint64_t len = qed_offset_into_cluster(s, acb->cur_pos);
    trace_qed_aio_write_prefill(s, acb, start, len, acb->cur_cluster);
    qed_copy_from_backing_file(s, start, len, acb->cur_cluster,
                                qed_aio_write_postfill, acb);
}