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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 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(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.

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), capabilities(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2004-05-27                           IOPL(2)