vio9p —
VirtIO 9p front-end driver
In conjunction with mount_9p(8),
  the vio9p driver enables a
  NetBSD system running as a VM guest to mount an
  exported file system by the host via virtio-9p. It exports a 9p end-point of
  virtio-9p via a character device file for
  mount_9p(8).
Each exported file system is assigned a character device and
    accessible via /dev/vio9p0,
    /dev/vio9p1 and so on, respectively, in exporting
    order by the host.
The following command mounts the first exported file system by the host at
  /mnt/9p:
# mount_9p -cu /dev/vio9p0 /mnt/9p
 
The vio9p driver first appeared in
  NetBSD 10.0.