IOPERM(2)                 (2017-09-15)                  IOPERM(2)

     NAME
          ioperm - set port input/output permissions

     SYNOPSIS
          #include <sys/io.h> /* for glibc */

          int ioperm(unsigned long from, unsigned long num, int
          turn_on

     DESCRIPTION
          ioperm() sets the port access permission bits for the call-
          ing thread for num bits starting from port address from. If
          turn_on is nonzero, then permission for the specified bits
          is enabled; otherwise it is disabled.  If turn_on is
          nonzero, the calling thread must be privileged
          (CAP_SYS_RAWIO).

          Before Linux 2.6.8, only the first 0x3ff I/O ports could be
          specified in this manner.  For more ports, the iopl(2) sys-
          tem call had to be used (with a level argument of 3).  Since
          Linux 2.6.8, 65,536 I/O ports can be specified.

          Permissions are inherited by the child created by fork(2)
          (but see NOTES).  Permissions are preserved across
          execve(2); this is useful for giving port access permissions
          to unprivileged programs.

          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
               Invalid values for from or num.

          EIO  (on PowerPC) This call is not supported.

          ENOMEM
               Out of memory.

          EPERM
               The calling thread has insufficient privilege.

     CONFORMING TO
          ioperm() is Linux-specific and should not be used in pro-
          grams intended to be portable.

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     IOPERM(2)                 (2017-09-15)                  IOPERM(2)

     NOTES
          The /proc/ioports file shows the I/O ports that are cur-
          rently allocated on the system.

          Before Linux 2.4, permissions were not inherited by a child
          created by fork(2).

          Glibc has an ioperm() prototype both in <sys/io.h> and in
          <sys/perm.h>. Avoid the latter, it is available on i386
          only.

     SEE ALSO
          iopl(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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