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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  not  inherited  by  the  child  process  created  by fork(2) and are not
       preserved across execve(2) (but see NOTES).

       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
       portable.

NOTES

       Glibc2  has  a  prototype both in <sys/io.h> and in <sys/perm.h>.  Avoid the latter, it is
       available on i386 only.

       Prior to Linux 3.7, on some architectures (such as i386), permissions  were  inherited  by
       the  child  produced  by  fork(2)  and were preserved across execve(2).  This behavior was
       inadvertently changed in Linux 3.7, and won't be reinstated.

SEE ALSO

       ioperm(2), outb(2), capabilities(7)

COLOPHON

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