convension about type argument on _IO macro

[Colin Vidal]

Hi all,

In LDDv3, chapter 6, on ioctl, macros IOCTQUANTIUM is defined with
_IO(SCULL_MAGIC, 3).

IOCT_* tells that a value (given directly as value through the argument)
is set to the device. However, no type is given to this macro.

It is not a big deal since this macro is just a helper to generate
identifiers, but, I wonder if there is any convention telling that we
should precise an argument only if it's a pointer ?

Thanks

- Colin