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outb(2) — Linux manual page

outb(2)                    System Calls Manualoutb(2)

NAME        top

       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

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <sys/io.h>unsigned char inb(unsigned shortport);unsigned char inb_p(unsigned shortport);unsigned short inw(unsigned shortport);unsigned short inw_p(unsigned shortport);unsigned int inl(unsigned shortport);unsigned int inl_p(unsigned shortport);void outb(unsigned charvalue, unsigned shortport);void outb_p(unsigned charvalue, unsigned shortport);void outw(unsigned shortvalue, unsigned shortport);void outw_p(unsigned shortvalue, unsigned shortport);void outl(unsigned intvalue, unsigned shortport);void outl_p(unsigned intvalue, unsigned shortport);void insb(unsigned long count;unsigned shortport, voidaddr[count],unsigned longcount);void insw(unsigned long count;unsigned shortport, voidaddr[count],unsigned longcount);void insl(unsigned long count;unsigned shortport, voidaddr[count],unsigned longcount);void outsb(unsigned long count;unsigned shortport, const voidaddr[count],unsigned longcount);void outsw(unsigned long count;unsigned shortport, const voidaddr[count],unsigned longcount);void outsl(unsigned long count;unsigned shortport, const voidaddr[count],unsigned longcount);

DESCRIPTION        top

       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.       They are primarily designed for internal kernel use, but can be       used from user space.       You must compile with-Oor-O2or similar.  The functions are       defined as inline macros, and will not be substituted in without       optimization enabled, causing unresolved references at link time.       You useioperm(2) or alternativelyiopl(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.

VERSIONS        top

outb() and friends are hardware-specific.  Thevalue argument is       passed first and theport argument is passed second, which is the       opposite order from most DOS implementations.

STANDARDS        top

       None.

SEE ALSO        top

ioperm(2),iopl(2)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-06-28outb(2)

Pages that refer to this page:ioperm(2), iopl(2)

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