uint16             59 kernel/virtio.h   uint16 flags;
uint16             60 kernel/virtio.h   uint16 next;
uint16             67 kernel/virtio.h   uint16 flags;     // always zero
uint16             68 kernel/virtio.h   uint16 idx;       // driver will write ring[idx] next
uint16             69 kernel/virtio.h   uint16 ring[NUM]; // descriptor numbers of chain heads
uint16             70 kernel/virtio.h   uint16 unused;
uint16             81 kernel/virtio.h   uint16 flags; // always zero
uint16             82 kernel/virtio.h   uint16 idx;   // device increments when it adds a ring[] entry
uint16             43 kernel/virtio_disk.c   uint16 used_idx; // we've looked this far in used[2..NUM].