iopl


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
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