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



NAME
       iopl - change I/O privilege level

SYNOPSIS
       #include <&lt;sys/io.h>&gt;

       int iopl(int level);

DESCRIPTION
       iopl() changes the I/O privilege level of the calling process, as spec-
       ified 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.

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  &lt;unistd.h&gt;.
       Glibc1  does  not  have  a  prototype.   Glibc2 has a prototype both in
       &lt;sys/io.h&gt; and in &lt;sys/perm.h&gt;.  Avoid the latter, it is  available  on
       i386 only.

SEE ALSO
       ioperm(2), capabilities(7)

COLOPHON
       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2004-05-27                           IOPL(2)