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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 calling process, as spec-
       ified by	the two	least significant bits 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(2) 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(2) and	execve(2).

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

       This call is mostly for the i386	architecture.  On many other architec-
       tures it	does not exist or will always return an	error.

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

ERRORS
       EINVAL level is greater than 3.

       ENOSYS This call	is unimplemented.

       EPERM  The calling process has insufficient privilege to	 call  iopl();
	      the CAP_SYS_RAWIO	capability is required to raise	the I/O	privi-
	      lege level above its current value.

CONFORMING TO
       iopl() is Linux-specific	and should not be used in  programs  that  are
       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), outb(2), capabilities(7)

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2013-03-15			       IOPL(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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