ring               69 kernel/virtio.h   uint16 ring[NUM]; // descriptor numbers of chain heads
ring               83 kernel/virtio.h   struct virtq_used_elem ring[NUM];
ring              275 kernel/virtio_disk.c   disk.avail->ring[disk.avail->idx % NUM] = idx[0];
ring              320 kernel/virtio_disk.c     int id = disk.used->ring[disk.used_idx % NUM].id;