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iopl(2)


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

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.



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