NAME    [Toc]    [Back]

       iopl - change I/O privilege level

SYNOPSIS    [Toc]    [Back]

       #include <sys/io.h>

       int iopl(int level);

DESCRIPTION    [Toc]    [Back]

       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 interrupts.
  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    [Toc]    [Back]

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

ERRORS    [Toc]    [Back]

       EINVAL level is greater than 3.

       EPERM  The current user is not the super-user.

NOTES FROM THE KERNEL SOURCE    [Toc]    [Back]

       iopl  has  to  be used when you want to access the I/O ports beyond the
       0x3ff range: to get the full 65536 ports bitmapped you'd  need  8kB  of
       bitmaps/process, which is a bit excessive.

CONFORMING TO    [Toc]    [Back]

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

COMPATIBILITY    [Toc]    [Back]

       Under libc5, the prototype for iopl() was given in <unistd.h>.

SEE ALSO    [Toc]    [Back]

       ioperm(2)



Linux 0.99.11			  1993-07-24			       IOPL(2)