.\" Copyright (c) 1995 Paul Gortmaker
.\" (gpg109@rsphy1.anu.edu.au)
.\" Wed Nov 29 10:58:54 EST 1995
.\"
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.TH OUTB 2 2020-11-01 "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 " port );
.BI "unsigned char inb_p(unsigned short " port );
.BI "unsigned short inw(unsigned short " port );
.BI "unsigned short inw_p(unsigned short " port );
.BI "unsigned int inl(unsigned short " port );
.BI "unsigned int inl_p(unsigned short " port );
.PP
.BI "void outb(unsigned char " value ", unsigned short " port );
.BI "void outb_p(unsigned char " value ", unsigned short " port );
.BI "void outw(unsigned short " value ", unsigned short " port );
.BI "void outw_p(unsigned short " value ", unsigned short " port );
.BI "void outl(unsigned int " value ", unsigned short " port );
.BI "void outl_p(unsigned int " value ", unsigned short " port );
.PP
.BI "void insb(unsigned short " port ", void *" addr ,
.BI "           unsigned long " count );
.BI "void insw(unsigned short " port ", void *" addr ,
.BI "           unsigned long " count );
.BI "void insl(unsigned short " port ", void *" addr ,
.BI "           unsigned long " count );
.BI "void outsb(unsigned short " port ", const void *" addr ,
.BI "           unsigned long " count );
.BI "void outsw(unsigned short " port ", const void *" addr ,
.BI "           unsigned long " count );
.BI "void outsl(unsigned short " port ", const void *" addr ,
.BI "           unsigned long " 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 5.10 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/.