.\" Copyright (c) 1995 Paul Gortmaker
.\" (gpg109@rsphy1.anu.edu.au)
.\" Wed Nov 29 10:58:54 EST 1995
.\"
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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 5.04 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/.