redhat man page for inw_p

OUTB(2) 						     Linux Programmer's Manual							   OUTB(2)

NAME
       outb, outw, outl, outsb, outsw, outsl - port output
       inb, inw, inl, insb, insw, insl - port input
       outb_p, outw_p, outl_p, inb_p, inw_p, inl_p - paused I/O

DESCRIPTION
       This  family  of  functions is used to do low level port input and output.  They are primarily designed for internal kernel use, but can be
       used from user space.

       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.

CONFORMING TO
       outb and friends are hardware specific. The port and value arguments are in the opposite order to most DOS implementations.

SEE ALSO
       ioperm(2), iopl(2)

Linux								    1995-11-29								   OUTB(2)