used_idx           43 kernel/virtio_disk.c   uint16 used_idx; // we've looked this far in used[2..NUM].
used_idx          318 kernel/virtio_disk.c   while (disk.used_idx != disk.used->idx) {
used_idx          320 kernel/virtio_disk.c     int id = disk.used->ring[disk.used_idx % NUM].id;
used_idx          329 kernel/virtio_disk.c     disk.used_idx += 1;