mirror of https://github.com/mkerrisk/man-pages
112 lines
3.5 KiB
Groff
112 lines
3.5 KiB
Groff
.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\" Portions extracted from linux/kernel/ioport.c (no copyright notice).
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Modified Tue Aug 1 16:47 1995 by Jochen Karrer
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.\" <cip307@cip.physik.uni-wuerzburg.de>
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.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added notes on capability requirements
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.\"
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.TH IOPL 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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iopl \- change I/O privilege level
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.SH SYNOPSIS
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.nf
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.B #include <sys/io.h>
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.PP
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.BI "int iopl(int " level );
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.fi
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.SH DESCRIPTION
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.BR iopl ()
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changes the I/O privilege level of the calling thread,
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as specified by the two least significant bits in
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.IR level .
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.PP
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The I/O privilege level for a normal thread is 0.
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Permissions are inherited from parents to children.
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.PP
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This call is deprecated, is significantly slower than
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.BR ioperm (2),
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and is only provided for older X servers which require
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access to all 65536 I/O ports.
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It is mostly for the i386 architecture.
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On many other architectures it does not exist or will always
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return an error.
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.SH RETURN VALUE
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EINVAL
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.I level
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is greater than 3.
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.TP
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.B ENOSYS
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This call is unimplemented.
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.TP
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.B EPERM
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The calling thread has insufficient privilege to call
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.BR iopl ();
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the
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.B CAP_SYS_RAWIO
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capability is required to raise the I/O privilege level
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above its current value.
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.SH CONFORMING TO
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.BR iopl ()
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is Linux-specific and should not be used in programs that are
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intended to be portable.
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.SH NOTES
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.\" Libc5 treats it as a system call and has a prototype in
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.\" .IR <unistd.h> .
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.\" Glibc1 does not have a prototype.
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Glibc2 has a prototype both in
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.I <sys/io.h>
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and in
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.IR <sys/perm.h> .
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Avoid the latter, it is available on i386 only.
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.PP
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Prior to Linux 5.5
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.BR iopl ()
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allowed the thread to disable interrupts while running
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at a higher I/O privilege level.
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This will probably crash the system, and is not recommended.
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.PP
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Prior to Linux 3.7,
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on some architectures (such as i386), permissions
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.I were
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inherited by the child produced by
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.BR fork (2)
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and were preserved across
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.BR execve (2).
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This behavior was inadvertently changed in Linux 3.7,
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and won't be reinstated.
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.SH SEE ALSO
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.BR ioperm (2),
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.BR outb (2),
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.BR capabilities (7)
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