System Calls Manual (i386)
NAME i386_iopl — change the i386 I/O privilege level
LIBRARY i386 Architecture Library (libi386, -li386)
DESCRIPTION i386_iopl() sets the i386 I/O privilege level to the value specified by iopl. This call is restricted to the super-user.
RETURN VALUES Upon successful completion, i386_iopl() returns 0. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.
() will fail if:
The caller was not the super-user, or the operation was not permitted at the current security level.
REFERENCES i386 Microprocessor Programmer's Reference Manual, Intel
WARNING You can really hose your machine if you enable user-level I/O and write to hardware ports without care.