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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 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

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