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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 thread, as specified by the two
       least significant bits in level.

       The I/O privilege level for a normal thread is 0.  Permissions are inherited from  parents
       to children.

       This  call is deprecated, is significantly slower than ioperm(2), and is only provided for
       older X servers which require access to all 65536 I/O ports.  It is mostly  for  the  i386
       architecture.   On  many  other  architectures  it does not exist or will always return an


       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 thread 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


       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  5.5  iopl()  allowed the thread to disable interrupts while running at a
       higher I/O privilege level.  This will probably crash the system, and is not recommended.

       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.


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


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