<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<HTML
><HEAD
><TITLE
> copy_[to/from]_user()
/
get_user()
/
put_user()
include/asm/uaccess.h
</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="Unreliable Guide To Hacking The Linux Kernel"
HREF="book1.html"><LINK
REL="UP"
TITLE="Common Routines"
HREF="c141.html"><LINK
REL="PREVIOUS"
TITLE="Common Routines"
HREF="c141.html"><LINK
REL="NEXT"
TITLE="kmalloc()/kfree()
include/linux/slab.h"
HREF="x180.html"></HEAD
><BODY
CLASS="SECT1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Unreliable Guide To Hacking The Linux Kernel</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="c141.html"
ACCESSKEY="P"
><<< Previous</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Common Routines</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x180.html"
ACCESSKEY="N"
>Next >>></A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="ROUTINES-COPY"
></A
><TT
CLASS="FUNCTION"
>copy_[to/from]_user()</TT
>
/
<TT
CLASS="FUNCTION"
>get_user()</TT
>
/
<TT
CLASS="FUNCTION"
>put_user()</TT
>
<TT
CLASS="FILENAME"
>include/asm/uaccess.h</TT
></H1
><P
> <I
CLASS="EMPHASIS"
>[SLEEPS]</I
>
</P
><P
> <TT
CLASS="FUNCTION"
>put_user()</TT
> and <TT
CLASS="FUNCTION"
>get_user()</TT
>
are used to get and put single values (such as an int, char, or
long) from and to userspace. A pointer into userspace should
never be simply dereferenced: data should be copied using these
routines. Both return <TT
CLASS="CONSTANT"
>-EFAULT</TT
> or 0.
</P
><P
> <TT
CLASS="FUNCTION"
>copy_to_user()</TT
> and
<TT
CLASS="FUNCTION"
>copy_from_user()</TT
> are more general: they copy
an arbitrary amount of data to and from userspace.
<DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="./stylesheet-images/caution.gif"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
> Unlike <TT
CLASS="FUNCTION"
>put_user()</TT
> and
<TT
CLASS="FUNCTION"
>get_user()</TT
>, they return the amount of
uncopied data (ie. <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> still means
success).
</P
></TD
></TR
></TABLE
></DIV
>
[Yes, this moronic interface makes me cringe. Please submit a
patch and become my hero --RR.]
</P
><P
> The functions may sleep implicitly. This should never be called
outside user context (it makes no sense), with interrupts
disabled, or a spinlock held.
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="c141.html"
ACCESSKEY="P"
><<< Previous</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x180.html"
ACCESSKEY="N"
>Next >>></A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Common Routines</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c141.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><TT
CLASS="FUNCTION"
>kmalloc()</TT
>/<TT
CLASS="FUNCTION"
>kfree()</TT
>
<TT
CLASS="FILENAME"
>include/linux/slab.h</TT
></TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
