redhat man page for iopl

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

NAME
       iopl - change I/O privilege level

SYNOPSIS
       #include <sys/io.h>

       int iopl(int level);

DESCRIPTION
       iopl changes the I/O privilege level of the current process, as specified in level.

       This call is necessary to allow 8514-compatible X servers to run under Linux.  Since these X servers require access to all 65536 I/O ports,
       the ioperm call is not sufficient.

       In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows the  process  to  disable  inter-
       rupts.  This will probably crash the system, and is not recommended.

       Permissions are inherited by fork and exec.

       The I/O privilege level for a normal process is 0.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EINVAL level is greater than 3.

       EPERM  The current user is not the super-user.

CONFORMING TO
       iopl is Linux specific and should not be used in processes intended to be portable.

NOTES
       Libc5  treats  it  as  a  system  call and has a prototype in <unistd.h>.  Glibc1 does not have a prototype. Glibc2 has a prototype both in
       <sys/io.h> and in <sys/perm.h>.	Avoid the latter, it is available on i386 only.

SEE ALSO
       ioperm(2)

Linux 0.99.11							    1993-07-24								   IOPL(2)