This family of functions is used to do low level port input and output. The out*
functions do port output, the in* functions do port input; the b-suffix
functions are byte-width and the w-suffix functions word-width; the _p-suffix
functions pause until the I/O completes.
They are primarily designed for internal kernel use, but can be used from user
You compile with -O or -O2 or similar. The functions are defined
as inline macros, and will not be substituted in without optimization enabled,
causing unresolved references at link time.
You use ioperm(2) or alternatively iopl(2) to tell the kernel to
allow the user space application to access the I/O ports in question. Failure
to do this will cause the application to receive a segmentation fault.