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Linux 2.6 - man page for iopl (linux section 2)

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 specified 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 interrupts.  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 architectures 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 privilege level above its current value.

CONFORMING TO
       iopl() is Linux-specific and should not be used in programs that are intended to be porta-
       ble.

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 3.55 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					    2013-03-15					  IOPL(2)


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