The
nullop() function provides a generic “null operation”. It always returns the value 0. The
voidop() function takes no arguments and does nothing.
The
enodev(),
enxio(),
enoioctl(),
enosys(), and
eopnotsupp() functions always fail, returning
ENODEV,
ENXIO,
ENOTTY,
ENOSYS, and
EOPNOTSUPP, respectively.