X86_64_IOPL(2) System Calls Manual (x86_64) X86_64_IOPL(2)
x86_64_iopl -- change the x86_64 I/O privilege level
x86_64 Architecture Library (libx86_64, -lx86_64)
x86_64_iopl() sets the x86_64 I/O privilege level to the value specified
by iopl. This call is restricted to the super-user.
Upon successful completion, x86_64_iopl() returns 0. Otherwise, a value
of -1 is returned and the global variable errno is set to indicate the
x86_64_iopl() will fail if:
[EPERM] The caller was not the super-user, or the operation was not
permitted at the current security level.
You can really hose your machine if you enable user-level I/O and write
to hardware ports without care.
NetBSD 6.1.5 July 3, 2002 NetBSD 6.1.5