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+.\" Copyright (c) 1993 Michael Haardt
+.\" (michael@moria.de)
+.\" Fri Apr  2 11:32:09 MET DST 1993
+.\"
+.\" SPDX-License-Identifier: GPL-2.0-or-later
+.\"
+.\" Modified Sat Jul 24 15:12:05 1993 by Rik Faith <faith@cs.unc.edu>
+.\" Modified Tue Aug  1 16:27    1995 by Jochen Karrer
+.\"                              <cip307@cip.physik.uni-wuerzburg.de>
+.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
+.\" Modified Mon Feb 15 17:28:41 CET 1999 by Andries E. Brouwer <aeb@cwi.nl>
+.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
+.\"     Added notes on capability requirements
+.\"
+.TH ioperm 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+ioperm \- set port input/output permissions
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <sys/io.h>
+.P
+.BI "int ioperm(unsigned long " from ", unsigned long " num ", int " turn_on );
+.fi
+.SH DESCRIPTION
+.BR ioperm ()
+sets the port access permission bits for the calling thread for
+.I num
+bits starting from port address
+.IR from .
+If
+.I turn_on
+is nonzero, then permission for the specified bits is enabled;
+otherwise it is disabled.
+If
+.I turn_on
+is nonzero, the calling thread must be privileged
+.RB ( CAP_SYS_RAWIO ).
+.P
+Before Linux 2.6.8,
+only the first 0x3ff I/O ports could be specified in this manner.
+For more ports, the
+.BR iopl (2)
+system call had to be used (with a
+.I level
+argument of 3).
+Since Linux 2.6.8, 65,536 I/O ports can be specified.
+.P
+Permissions are inherited by the child created by
+.BR fork (2)
+(but see NOTES).
+Permissions are preserved across
+.BR execve (2);
+this is useful for giving port access permissions to unprivileged
+programs.
+.P
+This call is mostly for the i386 architecture.
+On many other architectures it does not exist or will always
+return an error.
+.SH RETURN VALUE
+On success, zero is returned.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EINVAL
+Invalid values for
+.I from
+or
+.IR num .
+.TP
+.B EIO
+(on PowerPC) This call is not supported.
+.TP
+.B ENOMEM
+.\" Could not allocate I/O bitmap.
+Out of memory.
+.TP
+.B EPERM
+The calling thread has insufficient privilege.
+.SH VERSIONS
+glibc has an
+.BR ioperm ()
+prototype both in
+.I <sys/io.h>
+and in
+.IR <sys/perm.h> .
+Avoid the latter, it is available on i386 only.
+.SH STANDARDS
+Linux.
+.SH HISTORY
+Before Linux 2.4,
+permissions were not inherited by a child created by
+.BR fork (2).
+.SH NOTES
+The
+.I /proc/ioports
+file shows the I/O ports that are currently allocated on the system.
+.SH SEE ALSO
+.BR iopl (2),
+.BR outb (2),
+.BR capabilities (7)