IOPL(2)                   (2020-08-13)                    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
          thread, as specified by the two least significant bits in
          level.

          The I/O privilege level for a normal thread is 0.  Permis-
          sions 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 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 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.

     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 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.

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     IOPL(2)                   (2020-08-13)                    IOPL(2)

          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 5.10 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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