.\" Copyright (c) 1995 Paul Gortmaker

.\" (gpg109@rsphy1.anu.edu.au)

.\" Wed Nov 29 10:58:54 EST 1995

.\"

.\" %%%LICENSE_START(GPLv2+_DOC_FULL)

.\" This is free documentation; you can redistribute it and/or

.\" modify it under the terms of the GNU General Public License as

.\" published by the Free Software Foundation; either version 2 of

.\" the License, or (at your option) any later version.

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.\" and "executables" are to be interpreted as the output of any

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.\" This manual is distributed in the hope that it will be useful,

.\" but WITHOUT ANY WARRANTY; without even the implied warranty of

.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

.\" GNU General Public License for more details.

.\"

.\" You should have received a copy of the GNU General Public

.\" License along with this manual; if not, see

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.\" %%%LICENSE_END

.\"

.TH OUTB 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

outb, outw, outl, outsb, outsw, outsl,

inb, inw, inl, insb, insw, insl,

outb_p, outw_p, outl_p, inb_p, inw_p, inl_p \- port I/O

.SH SYNOPSIS

.nf

.B #include <sys/io.h>

.PP

.BI "unsigned char inb(unsigned short int " port );

.BI "unsigned char inb_p(unsigned short int " port );

.BI "unsigned short int inw(unsigned short int " port );

.BI "unsigned short int inw_p(unsigned short int " port );

.BI "unsigned int inl(unsigned short int " port );

.BI "unsigned int inl_p(unsigned short int " port );

.PP

.BI "void outb(unsigned char " value ", unsigned short int " port );

.BI "void outb_p(unsigned char " value ", unsigned short int " port );

.BI "void outw(unsigned short int " value ", unsigned short int " port );

.BI "void outw_p(unsigned short int " value ", unsigned short int " port );

.BI "void outl(unsigned int " value ", unsigned short int " port );

.BI "void outl_p(unsigned int " value ", unsigned short int " port );

.PP

.BI "void insb(unsigned short int " port ", void *" addr ,

.BI "           unsigned long int " count );

.BI "void insw(unsigned short int " port ", void *" addr ,

.BI "           unsigned long int " count );

.BI "void insl(unsigned short int " port ", void *" addr ,

.BI "           unsigned long int " count );

.BI "void outsb(unsigned short int " port ", const void *" addr ,

.BI "           unsigned long int " count );

.BI "void outsw(unsigned short int " port ", const void *" addr ,

.BI "           unsigned long int " count );

.BI "void outsl(unsigned short int " port ", const void *" addr ,

.BI "           unsigned long int " count );

.fi

.SH DESCRIPTION

This family of functions is used to do low-level port input and output.

The out* functions do port output, the in* functions do port input;

the b-suffix functions are byte-width and the w-suffix functions

word-width; the _p-suffix functions pause until the I/O completes.

.PP

They are primarily designed for internal kernel use,

but can be used from user space.

.\" , given the following information

.\" in addition to that given in

.\" .BR outb (9).

.PP

You must compile with \fB\-O\fP or \fB\-O2\fP or similar.

The functions

are defined as inline macros, and will not be substituted in without

optimization enabled, causing unresolved references at link time.

.PP

You use

.BR ioperm (2)

or alternatively

.BR iopl (2)

to tell the kernel to allow the user space application to access the

I/O ports in question.

Failure to do this will cause the application

to receive a segmentation fault.

.SH CONFORMING TO

.BR outb ()

and friends are hardware-specific.

The

.I value

argument is passed first and the

.I port

argument is passed second,

which is the opposite order from most DOS implementations.

.SH SEE ALSO

.BR ioperm (2),

.BR iopl (2)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.