| IO(4) | Device Drivers Manual (i386) | IO(4) | 
io —
After opening /dev/io for writing the process is granted full I/O privileges; closing the returned file descriptor does not result in revocation of these privileges. The new I/O privileges can be useful in order to write userland programs that handle some hardware directly.
The entire access control is handled by the file access permissions of /dev/io, so care should be taken in granting rights for this device.
I/O privilege on access to /dev/io is only
    granted if the kernel was built with the COMPAT_10
    option.
io file appeared in NetBSD
  1.0 after it was in the kernel for some time.
| January 1, 1996 | NetBSD 10.1 |