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       iopl - change I/O privilege level


       #include <sys/io.h>

       int iopl(int level);


       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

       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.


       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.


       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.


       iopl()  is  Linux-specific  and should not be used in programs that are
       intended to be portable.


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


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


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