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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
	  "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
<chapter id='Window_and_Session_Manager_Functions'>
<title>Window and Session Manager Functions</title>

<para>
Although it is difficult to categorize functions as exclusively for an application,
a window manager, or a session manager, the functions in this chapter are most
often used by window managers and session managers. It is not expected that
these functions will be used by most application programs. Xlib provides
management functions to:
</para>

<itemizedlist>
  <listitem><para>Change the parent of a window</para></listitem>
  <listitem><para>Control the lifetime of a window</para></listitem>
  <listitem><para>Manage installed colormaps</para></listitem>
  <listitem><para>Set and retrieve the font search path</para></listitem>
  <listitem><para>Grab the server</para></listitem>
  <listitem><para>Kill a client</para></listitem>
  <listitem><para>Control the screen saver</para></listitem>
  <listitem><para>Control host access</para></listitem>
</itemizedlist>

<sect1 id="Changing_the_Parent_of_a_Window">
<title>Changing the Parent of a Window</title>
<!-- .XS -->
<!-- (SN Changing the Parent of a Window  -->
<!-- .XE -->
<para>
<!-- .LP -->
To change a window's parent to another window on the same screen, use
<xref linkend='XReparentWindow' xrefstyle='select: title'/>.
There is no way to move a window between screens.
</para>
<indexterm significance="preferred"><primary>XReparentWindow</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XReparentWindow'>
<funcprototype>
  <funcdef><function>XReparentWindow</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Window<parameter> w</parameter></paramdef>
  <paramdef>Window<parameter> parent</parameter></paramdef>
  <paramdef>intx,<parameter> y</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the window.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>parent</emphasis>
    </term>
    <listitem>
      <para>
Specifies the parent window.
<!-- .ds Xy \ of the position in the new parent window -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>x</emphasis>
    </term>
    <listitem>
      <para>
<!-- .br -->
<!-- .ns -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>y</emphasis>
    </term>
    <listitem>
      <para>
Specify the x and y coordinates(Xy.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
If the specified window is mapped,
<xref linkend='XReparentWindow' xrefstyle='select: title'/>
automatically performs an
<systemitem>UnmapWindow</systemitem>
request on it, removes it from its current position in the hierarchy,
and inserts it as the child of the specified parent.
The window is placed in the stacking order on top with respect to
sibling windows.
</para>
<para>
<!-- .LP -->
After reparenting the specified window,
<xref linkend='XReparentWindow' xrefstyle='select: title'/>
causes the X server to generate a
<symbol>ReparentNotify</symbol>
event.
The override_redirect member returned in this event is
set to the window's corresponding attribute.
Window manager clients usually should ignore this window if this member
is set to
<symbol>True</symbol>.
Finally, if the specified window was originally mapped,
the X server automatically performs a
<systemitem>MapWindow</systemitem>
request on it.
</para>
<para>
<!-- .LP -->
The X server performs normal exposure processing on formerly obscured
windows.
The X server might not generate 
<symbol>Expose</symbol>
events for regions from the initial
<systemitem>UnmapWindow</systemitem>
request that are immediately obscured by the final
<systemitem>MapWindow</systemitem>
request.
A
<errorname>BadMatch</errorname>
error results if:
</para>
<itemizedlist>
  <listitem>
    <para>
The new parent window is not on the same screen as
the old parent window.
    </para>
  </listitem>
  <listitem>
    <para>
The new parent window is the specified window or an inferior of the
specified window.
    </para>
  </listitem>
  <listitem>
    <para>
The new parent is
<symbol>InputOnly</symbol>,
and the window is not.
    </para>
  </listitem>
  <listitem>
    <para>
The specified window has a
<symbol>ParentRelative</symbol>
background, and the new parent window is not the same depth as the
specified window.
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
<xref linkend='XReparentWindow' xrefstyle='select: title'/>
can generate
<errorname>BadMatch</errorname>
and
<errorname>BadWindow</errorname>
errors.
</para>
</sect1>
<sect1 id="Controlling_the_Lifetime_of_a_Window">
<title>Controlling the Lifetime of a Window</title>
<!-- .XS -->
<!-- (SN Controlling the Lifetime of a Window  -->
<!-- .XE -->
<para>
<!-- .LP -->
The save-set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection close,
should not be destroyed and should be remapped if they are unmapped.
For further information about close-connection processing,
see <link linkend='Using_X_Server_Connection_Close_Operations'>section 2.6</link>.
To allow an application's window to survive when a window manager that
has reparented a window fails,
Xlib provides the save-set functions that you can 
use to control the longevity of subwindows
that are normally destroyed when the parent is destroyed.
For example, a window manager that wants to add decoration
to a window by adding a frame might reparent an application's
window. 
When the frame is destroyed,
the application's window should not be destroyed 
but be returned to its previous place in the window hierarchy.
</para>
<para>
<!-- .LP -->
The X server automatically removes windows from the save-set
when they are destroyed.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To add or remove a window from the client's save-set, use
<xref linkend='XChangeSaveSet' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XChangeSaveSet</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XChangeSaveSet'>
<funcprototype>
  <funcdef><function>XChangeSaveSet</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Window<parameter> w</parameter></paramdef>
  <paramdef>int<parameter> change_mode</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Wi that you want to add to or delete from the client's save-set -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the window (Wi.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>change_mode</emphasis>
    </term>
    <listitem>
      <para>
Specifies the mode.
You can pass
<symbol>SetModeInsert</symbol>
or
<symbol>SetModeDelete</symbol>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
Depending on the specified mode,
<xref linkend='XChangeSaveSet' xrefstyle='select: title'/>
either inserts or deletes the specified window from the client's save-set. 
The specified window must have been created by some other client,
or a
<errorname>BadMatch</errorname>
error results.
</para>
<para>
<!-- .LP -->
<xref linkend='XChangeSaveSet' xrefstyle='select: title'/>
can generate
<errorname>BadMatch</errorname>,
<errorname>BadValue</errorname>,
and
<errorname>BadWindow</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To add a window to the client's save-set, use
<xref linkend='XAddToSaveSet' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XAddToSaveSet</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XAddToSaveSet'>
<funcprototype>
  <funcdef><function>XAddToSaveSet</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Window<parameter> w</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Wi that you want to add to the client's save-set -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the window (Wi.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XAddToSaveSet' xrefstyle='select: title'/>
function adds the specified window to the client's save-set.
The specified window must have been created by some other client,
or a
<errorname>BadMatch</errorname>
error results.
</para>
<para>
<!-- .LP -->
<xref linkend='XAddToSaveSet' xrefstyle='select: title'/>
can generate
<errorname>BadMatch</errorname>
and
<errorname>BadWindow</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To remove a window from the client's save-set, use
<xref linkend='XRemoveFromSaveSet' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XRemoveFromSaveSet</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XRemoveFromSaveSet'>
<funcprototype>
  <funcdef><function>XRemoveFromSaveSet</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Window<parameter> w</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Wi that you want to delete from the client's save-set -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the window (Wi.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XRemoveFromSaveSet' xrefstyle='select: title'/>
function removes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
<errorname>BadMatch</errorname>
error results.
</para>
<para>
<!-- .LP -->
<xref linkend='XRemoveFromSaveSet' xrefstyle='select: title'/>
can generate
<errorname>BadMatch</errorname>
and
<errorname>BadWindow</errorname>
errors.
</para>
</sect1>
<sect1 id="Managing_Installed_Colormaps">
<title>Managing Installed Colormaps</title>
<!-- .XS -->
<!-- (SN Managing Installed Colormaps -->
<!-- .XE -->
<para>
<!-- .LP -->
The X server maintains a list of installed colormaps.
Windows using these colormaps are guaranteed to display with
correct colors; windows using other colormaps may or may not display
with correct colors.
Xlib provides functions that you can use to install a colormap, 
uninstall a colormap, and obtain a list of installed colormaps.
</para>
<para>
<!-- .LP -->
At any time,
there is a subset of the installed maps that is viewed as an ordered list
and is called the required list.
The length of the required list is at most M,
where M is the minimum number of installed colormaps specified for the screen
in the connection setup.
The required list is maintained as follows.
When a colormap is specified to
<xref linkend='XInstallColormap' xrefstyle='select: title'/>,
it is added to the head of the list;
the list is truncated at the tail, if necessary, to keep its length to 
at most M.
When a colormap is specified to
<xref linkend='XUninstallColormap' xrefstyle='select: title'/>
and it is in the required list,
it is removed from the list.
A colormap is not added to the required list when it is implicitly installed
by the X server,
and the X server cannot implicitly uninstall a colormap that is in the
required list.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To install a colormap, use
<xref linkend='XInstallColormap' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XInstallColormap</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XInstallColormap'>
<funcprototype>
  <funcdef><function>XInstallColormap</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Colormap<parameter> colormap</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>colormap</emphasis>
    </term>
    <listitem>
      <para>
Specifies the colormap.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XInstallColormap' xrefstyle='select: title'/>
function installs the specified colormap for its associated screen.
All windows associated with this colormap immediately display with
true colors.
You associated the windows with this colormap when you created them by calling
<xref linkend='XCreateWindow' xrefstyle='select: title'/>,
<xref linkend='XCreateSimpleWindow' xrefstyle='select: title'/>,
<xref linkend='XChangeWindowAttributes' xrefstyle='select: title'/>,
or
<xref linkend='XSetWindowColormap' xrefstyle='select: title'/>.
</para>
<para>
<!-- .LP -->
If the specified colormap is not already an installed colormap, 
the X server generates a
<symbol>ColormapNotify</symbol>
event on each window that has that colormap.
In addition, for every other colormap that is installed as 
a result of a call to
<xref linkend='XInstallColormap' xrefstyle='select: title'/>,
the X server generates a
<symbol>ColormapNotify</symbol>
event on each window that has that colormap.
</para>
<para>
<!-- .LP -->
<xref linkend='XInstallColormap' xrefstyle='select: title'/>
can generate a
<errorname>BadColor</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To uninstall a colormap, use
<xref linkend='XUninstallColormap' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XUninstallColormap</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XUninstallColormap'>
<funcprototype>
  <funcdef><function>XUninstallColormap</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Colormap<parameter> colormap</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>colormap</emphasis>
    </term>
    <listitem>
      <para>
Specifies the colormap.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XUninstallColormap' xrefstyle='select: title'/>
function removes the specified colormap from the required
list for its screen.
As a result,
the specified colormap might be uninstalled, 
and the X server might implicitly install or uninstall additional colormaps.
Which colormaps get installed or uninstalled is server dependent
except that the required list must remain installed.
</para>
<para>
<!-- .LP -->
If the specified colormap becomes uninstalled, 
the X server generates a
<symbol>ColormapNotify</symbol>
event on each window that has that colormap.
In addition, for every other colormap that is installed or uninstalled as a 
result of a call to 
<xref linkend='XUninstallColormap' xrefstyle='select: title'/>,
the X server generates a
<symbol>ColormapNotify</symbol>
event on each window that has that colormap.
</para>
<para>
<!-- .LP -->
<xref linkend='XUninstallColormap' xrefstyle='select: title'/>
can generate a
<errorname>BadColor</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To obtain a list of the currently installed colormaps for a given screen, use
<xref linkend='XListInstalledColormaps' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XListInstalledColormaps</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XListInstalledColormaps'>
<funcprototype>
  <funcdef>Colormap *<function>XListInstalledColormaps</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>Window<parameter> w</parameter></paramdef>
  <paramdef>int<parameter> *num_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Wi that determines the screen -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the window (Wi.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the number of currently installed colormaps.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XListInstalledColormaps' xrefstyle='select: title'/>
function returns a list of the currently installed colormaps for the screen 
of the specified window.
The order of the colormaps in the list is not significant
and is no explicit indication of the required list.
When the allocated list is no longer needed,
free it by using
<xref linkend='XFree' xrefstyle='select: title'/>.
</para>
<para>
<!-- .LP -->
<xref linkend='XListInstalledColormaps' xrefstyle='select: title'/>
can generate a
<errorname>BadWindow</errorname>
error.
</para>
</sect1>
<sect1 id="Setting_and_Retrieving_the_Font_Search_Path">
<title>Setting and Retrieving the Font Search Path</title>
<!-- .XS -->
<!-- (SN Setting and Retrieving the Font Search Path  -->
<!-- .XE -->
<para>
<!-- .LP -->
The set of fonts available from a server depends on a font
search path.  Xlib provides functions to set and retrieve the
search path for a server.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To set the font search path, use
<xref linkend='XSetFontPath' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XSetFontPath</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XSetFontPath'>
<funcprototype>
  <funcdef><function>XSetFontPath</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>char<parameter> **directories</parameter></paramdef>
  <paramdef>int<parameter> ndirs</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>directories</emphasis>
    </term>
    <listitem>
      <para>
Specifies the directory path used to look for a font.
Setting the path to the empty list restores the default path defined
for the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>ndirs</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of directories in the path.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XSetFontPath' xrefstyle='select: title'/>
function defines the directory search path for font lookup.
There is only one search path per X server, not one per client.
The encoding and interpretation of the strings are implementation-dependent,
but typically they specify directories or font servers to be searched 
in the order listed.
An X server is permitted to cache font information internally;
for example, it might cache an entire font from a file and not
check on subsequent opens of that font to see if the underlying
font file has changed.
However,
when the font path is changed,
the X server is guaranteed to flush all cached information about fonts 
for which there currently are no explicit resource IDs allocated.
The meaning of an error from this request is implementation-dependent.
</para>
<para>
<!-- .LP -->
<xref linkend='XSetFontPath' xrefstyle='select: title'/>
can generate a
<errorname>BadValue</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To get the current font search path, use
<xref linkend='XGetFontPath' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XGetFontPath</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XGetFontPath'>
<funcprototype>
  <funcdef>char **<function>XGetFontPath</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>int<parameter> *npaths_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>npaths_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the number of strings in the font path array.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XGetFontPath' xrefstyle='select: title'/>
function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent
and are not intended to be interpreted by client applications.
When it is no longer needed,
the data in the font path should be freed by using
<xref linkend='XFreeFontPath' xrefstyle='select: title'/>.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To free data returned by
<xref linkend='XGetFontPath' xrefstyle='select: title'/>,
use
<xref linkend='XFreeFontPath' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XFreeFontPath</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XFreeFontPath'>
<funcprototype>
  <funcdef><function>XFreeFontPath</function></funcdef>
  <paramdef>char<parameter> **list</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>list</emphasis>
    </term>
    <listitem>
      <para>
Specifies the array of strings you want to free.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XFreeFontPath' xrefstyle='select: title'/>
function
frees the data allocated by
<xref linkend='XGetFontPath' xrefstyle='select: title'/>.
</para>
</sect1>
<sect1 id='Grabbing_the_Server'>
<title>Grabbing the Server</title>
<!-- .XS -->
<!-- (SN Grabbing the Server  -->
<!-- .XE -->
<para>
<!-- .LP -->
Xlib provides functions that you can use to grab and ungrab the server.
These functions can be used to control processing of output on other
connections by the window system server.
While the server is grabbed,
no processing of requests or close downs on any other connection will occur.
A client closing its connection automatically ungrabs the server.
<indexterm><primary>Menus</primary></indexterm>
<indexterm><primary>Window</primary><secondary>managers</secondary></indexterm>
Although grabbing the server is highly discouraged, it is sometimes necessary.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To grab the server, use
<xref linkend='XGrabServer' xrefstyle='select: title'/>.
</para>
<indexterm><primary>Server</primary><secondary>grabbing</secondary></indexterm>
<indexterm><primary>Grabbing</primary><secondary>server</secondary></indexterm>
<indexterm significance="preferred"><primary>XGrabServer</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XGrabServer'>
<funcprototype>
  <funcdef><function>XGrabServer</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XGrabServer' xrefstyle='select: title'/>
function disables processing of requests and close downs on all other 
connections than the one this request arrived on.
You should not grab the X server any more than is absolutely necessary.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To ungrab the server, use
<xref linkend='XUngrabServer' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XUngrabServer</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XUngrabServer'>
<funcprototype>
  <funcdef><function>XUngrabServer</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XUngrabServer' xrefstyle='select: title'/>
function restarts processing of requests and close downs on other connections.
You should avoid grabbing the X server as much as possible.
</para>
</sect1>
<sect1 id="Killing_Clients">
<title>Killing Clients</title>
<!-- .XS -->
<!-- (SN Killing Clients  -->
<!-- .XE -->
<para>
<!-- .LP -->
Xlib provides a function to cause the connection to
a client to be closed and its resources to be destroyed.
To destroy a client, use
<xref linkend='XKillClient' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XKillClient</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XKillClient'>
<funcprototype>
  <funcdef><function>XKillClient</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>XID<parameter> resource</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>resource</emphasis>
    </term>
    <listitem>
      <para>
Specifies any resource associated with the client that you want to destroy or
<symbol>AllTemporary</symbol>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XKillClient' xrefstyle='select: title'/>
function
forces a close down of the client
that created the resource
if a valid resource is specified.
If the client has already terminated in
either 
<symbol>RetainPermanent</symbol>
or 
<symbol>RetainTemporary</symbol>
mode, all of the client's
resources are destroyed.
If 
<symbol>AllTemporary</symbol>
is specified, the resources of all clients that have terminated in
<symbol>RetainTemporary</symbol>
are destroyed (see <link linkend="Closing_the_Display">section 2.5</link>).
This permits implementation of window manager facilities that aid debugging.
A client can set its close-down mode to
<symbol>RetainTemporary</symbol>.
If the client then crashes,
its windows would not be destroyed. 
The programmer can then inspect the application's window tree 
and use the window manager to destroy the zombie windows.
</para>
<para>
<!-- .LP -->
<xref linkend='XKillClient' xrefstyle='select: title'/>
can generate a
<errorname>BadValue</errorname>
error.
</para>
</sect1>
<sect1 id='Controlling_the_Screen_Saver'>
<title>Controlling the Screen Saver</title>
<!-- .XS -->
<!-- (SN Controlling the Screen Saver  -->
<!-- .XE -->
<para>
<!-- .LP -->
Xlib provides functions that you can use to set or reset the mode 
of the screen saver, to force or activate the screen saver,
or to obtain the current screen saver values.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To set the screen saver mode, use
<xref linkend='XSetScreenSaver' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XSetScreenSaver</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XSetScreenSaver'>
<funcprototype>
  <funcdef><function>XSetScreenSaver</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>inttimeout,<parameter> interval</parameter></paramdef>
  <paramdef>int<parameter> prefer_blanking</parameter></paramdef>
  <paramdef>int<parameter> allow_exposures</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>timeout</emphasis>
    </term>
    <listitem>
      <para>
Specifies the timeout, in seconds, until the screen saver turns on.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>interval</emphasis>
    </term>
    <listitem>
      <para>
Specifies the interval, in seconds, between screen saver alterations.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>prefer_blanking</emphasis>
    </term>
    <listitem>
      <para>
Specifies how to enable screen blanking.
You can pass
<symbol>DontPreferBlanking</symbol>,
<symbol>PreferBlanking</symbol>,
or
<symbol>DefaultBlanking</symbol>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>allow_exposures</emphasis>
    </term>
    <listitem>
      <para>
Specifies the screen save control values.
You can pass
<symbol>DontAllowExposures</symbol>,
<symbol>AllowExposures</symbol>,
or
<symbol>DefaultExposures</symbol>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
Timeout and interval are specified in seconds. 
A timeout of 0 disables the screen saver 
(but an activated screen saver is not deactivated),
and a timeout of &minus;1 restores the default.
Other negative values generate a
<errorname>BadValue</errorname>
error.
If the timeout value is nonzero, 
<xref linkend='XSetScreenSaver' xrefstyle='select: title'/>
enables the screen saver.
An interval of 0 disables the random-pattern motion.
If no input from devices (keyboard, mouse, and so on) is generated 
for the specified number of timeout seconds once the screen saver is enabled,
the screen saver is activated.
</para>
<para>
<!-- .LP -->
For each screen, 
if blanking is preferred and the hardware supports video blanking, 
the screen simply goes blank.  
Otherwise, if either exposures are allowed or the screen can be regenerated 
without sending 
<symbol>Expose</symbol>
events to clients, 
the screen is tiled with the root window background tile randomly 
re-origined each interval seconds.
Otherwise, the screens' state do not change, 
and the screen saver is not activated.
The screen saver is deactivated,
and all screen states are restored at the next
keyboard or pointer input or at the next call to
<xref linkend='XForceScreenSaver' xrefstyle='select: title'/>
with mode
<symbol>ScreenSaverReset</symbol>.
</para>
<para>
<!-- .LP -->
If the server-dependent screen saver method supports periodic change,
the interval argument serves as a hint about how long the change period
should be, and zero hints that no periodic change should be made.
Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling
the screen with the root window background tile, randomly re-origined
periodically.
</para>
<para>
<!-- .LP -->
<xref linkend='XSetScreenSaver' xrefstyle='select: title'/>
can generate a
<errorname>BadValue</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To force the screen saver on or off, use
<xref linkend='XForceScreenSaver' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XForceScreenSaver</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XForceScreenSaver'>
<funcprototype>
  <funcdef><function>XForceScreenSaver</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>int<parameter> mode</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>mode</emphasis>
    </term>
    <listitem>
      <para>
Specifies the mode that is to be applied.
You can pass
<symbol>ScreenSaverActive</symbol>
or
<symbol>ScreenSaverReset</symbol>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
If the specified mode is 
<symbol>ScreenSaverActive</symbol>
and the screen saver currently is deactivated,
<xref linkend='XForceScreenSaver' xrefstyle='select: title'/>
activates the screen saver even if the screen saver had been disabled
with a timeout of zero.
If the specified mode is 
<symbol>ScreenSaverReset</symbol>
and the screen saver currently is enabled,
<xref linkend='XForceScreenSaver' xrefstyle='select: title'/>
deactivates the screen saver if it was activated,
and the activation timer is reset to its initial state 
(as if device input had been received).
</para>
<para>
<!-- .LP -->
<xref linkend='XForceScreenSaver' xrefstyle='select: title'/>
can generate a
<errorname>BadValue</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To activate the screen saver, use
<xref linkend='XActivateScreenSaver' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XActivateScreenSaver</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XActivateScreenSaver'>
<funcprototype>
  <funcdef><function>XActivateScreenSaver</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
<!-- .sp -->
To reset the screen saver, use
<xref linkend='XResetScreenSaver' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XResetScreenSaver</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XResetScreenSaver'>
<funcprototype>
  <funcdef><function>XResetScreenSaver</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
<!-- .sp -->
To get the current screen saver values, use
<xref linkend='XGetScreenSaver' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XGetScreenSaver</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XGetScreenSaver'>
<funcprototype>
  <funcdef><function>XGetScreenSaver</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>int*timeout_return,<parameter> *interval_return</parameter></paramdef>
  <paramdef>int<parameter> *prefer_blanking_return</parameter></paramdef>
  <paramdef>int<parameter> *allow_exposures_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>timeout_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the timeout, in seconds, until the screen saver turns on.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>interval_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the interval between screen saver invocations.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>prefer_blanking_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the current screen blanking preference
(<symbol>DontPreferBlanking</symbol>,
<symbol>PreferBlanking</symbol>,
or
<symbol>DefaultBlanking</symbol>).
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>allow_exposures_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the current screen save control value
(<symbol>DontAllowExposures</symbol>,
<symbol>AllowExposures</symbol>,
or
<symbol>DefaultExposures</symbol>).
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
</para>
</sect1>
<sect1 id="Controlling_Host_Access">
<title>Controlling Host Access</title>
<!-- .XS -->
<!-- (SN Controlling Host Access  -->
<!-- .XE -->
<para>
<!-- .LP -->
This section discusses how to:
</para>
<itemizedlist>
  <listitem>
    <para>
Add, get, or remove hosts from the access control list
    </para>
  </listitem>
  <listitem>
    <para>
Change, enable, or disable access
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
<indexterm><primary>Access control list</primary></indexterm>
<indexterm><primary>Authentication</primary></indexterm>
X does not provide any protection on a per-window basis.
If you find out the resource ID of a resource, you can manipulate it.
To provide some minimal level of protection, however,
connections are permitted only from machines you trust.
This is adequate on single-user workstations but obviously
breaks down on timesharing machines.
Although provisions exist in the X protocol for proper connection
authentication, the lack of a standard authentication server
leaves host-level access control as the only common mechanism.
</para>
<para>
<!-- .LP -->
<indexterm><primary>Default Protection</primary></indexterm>
The initial set of hosts allowed to open connections typically consists of:
</para>
<itemizedlist>
  <listitem>
    <para>
The host the window system is running on.
    </para>
  </listitem>
  <listitem>
    <para>
On <acronym>POSIX</acronym>-conformant systems, each host listed in the
<filename>/etc/X<replaceable>?</replaceable>.hosts</filename>
file.
The ? indicates the number of the
display.
<indexterm><primary>Files</primary><secondary><filename>/etc/X<replaceable>?</replaceable>.hosts</filename></secondary></indexterm>
This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.
    </para>
  </listitem>
</itemizedlist>
<para>
<!-- .LP -->
If a host is not in the access control list when the access control 
mechanism is enabled and if the host attempts to establish a connection,
the server refuses the connection.
To change the access list,
the client must reside on the same host as the server and/or must
have been granted permission in the initial authorization at connection
setup.
</para>
<para>
<!-- .LP -->
Servers also can implement other access control policies in addition to
or in place of this host access facility.
For further information about other access control implementations,
see <olink targetdoc='x11protocol' targetptr='Connection_Setup'
><citetitle>X Window System Protocol</citetitle></olink>.
</para>
<sect2 id="Adding_Getting_or_Removing_Hosts">
<title>Adding, Getting, or Removing Hosts</title>
<!-- .XS -->
<!-- (SN Adding, Getting, or Removing Hosts  -->
<!-- .XE -->
<para>
<!-- .LP -->
Xlib provides functions that you can use to add, get, or remove hosts
from the access control list.
All the host access control functions use the 
<structname>XHostAddress</structname>
structure, which contains:
</para>
<para>
<!-- .LP -->
<indexterm significance="preferred"><primary>XHostAddress</primary></indexterm>
<!-- .sM -->
<literallayout class="monospaced">
<!-- .TA .5i 3i -->
<!-- .ta .5i 3i -->
typedef struct {
     int family;        /* for example FamilyInternet */
     int length;        /* length of address, in bytes */
     char *address;     /* pointer to where to find the address */
} XHostAddress;
</literallayout>
</para>
<para>
<!-- .LP -->
<!-- .eM -->
The family member specifies which protocol address family to use 
(for example, <acronym>TCP</acronym>/<acronym>IP</acronym> or DECnet) and can be
<symbol>FamilyInternet</symbol>,
<symbol>FamilyInternet6</symbol>,
<symbol>FamilyServerInterpreted</symbol>,
<symbol>FamilyDECnet</symbol>,
or
<symbol>FamilyChaos</symbol>.
The length member specifies the length of the address in bytes.
The address member specifies a pointer to the address.
</para>
<para>
<!-- .LP -->
For <acronym>TCP</acronym>/<acronym>IP</acronym>, the address should be in network byte order.
For <acronym>IP</acronym> version 4 addresses, the family should be FamilyInternet
and the length should be 4 bytes.  For <acronym>IP</acronym> version 6 addresses, the
family should be FamilyInternet6 and the length should be 16 bytes.
</para>
<para>
<!-- .LP -->
For the DECnet family, 
the server performs no automatic swapping on the address bytes.
A Phase IV address is 2 bytes long.
The first byte contains the least significant 8 bits of the node number.
The second byte contains the most significant 2 bits of the
node number in the least significant 2 bits of the byte
and the area in the most significant 6 bits of the byte.
</para>
<para>
<!-- .LP -->
For the ServerInterpreted family, the length is ignored and the address 
member is a pointer to a 
<structname>XServerInterpretedAddress</structname>
structure, which contains:
</para>
<para>
<!-- .LP -->
<indexterm significance="preferred"><primary>XServerInterpretedAddress</primary></indexterm>
<!-- .sM -->
<literallayout class="monospaced">
<!-- .TA .5i 3i -->
<!-- .ta .5i 3i -->
typedef struct {
     int typelength;     /* length of type string, in bytes */
     int valuelength;    /* length of value string, in bytes */
     char *type;         /* pointer to where to find the type string */
     char *value;        /* pointer to where to find the address */
} XServerInterpretedAddress;
</literallayout>
</para>
<para>
<!-- .LP -->
<!-- .eM -->
The type and value members point to strings representing the type and value of
the server interpreted entry.  These strings may not be NULL-terminated so care
should be used when accessing them.  The typelength and valuelength members
specify the length in byte of the type and value strings.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To add a single host, use
<xref linkend='XAddHost' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XAddHost</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XAddHost'>
<funcprototype>
  <funcdef><function>XAddHost</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>XHostAddress<parameter> *host</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Ho added -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>host</emphasis>
    </term>
    <listitem>
      <para>
Specifies the host that is to be (Ho.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XAddHost' xrefstyle='select: title'/>
function adds the specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
<errorname>BadAccess</errorname>
error results.
</para>
<para>
<!-- .LP -->
<xref linkend='XAddHost' xrefstyle='select: title'/>
can generate
<errorname>BadAccess</errorname>
and
<errorname>BadValue</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To add multiple hosts at one time, use
<xref linkend='XAddHosts' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XAddHosts</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XAddHosts'>
<funcprototype>
  <funcdef><function>XAddHosts</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>XHostAddress<parameter> *hosts</parameter></paramdef>
  <paramdef>int<parameter> num_hosts</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Ho added -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>hosts</emphasis>
    </term>
    <listitem>
      <para>
Specifies each host that is to be (Ho.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_hosts</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of hosts.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XAddHosts' xrefstyle='select: title'/>
function adds each specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
<errorname>BadAccess</errorname>
error results.
</para>
<para>
<!-- .LP -->
<xref linkend='XAddHosts' xrefstyle='select: title'/>
can generate
<errorname>BadAccess</errorname>
and
<errorname>BadValue</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To obtain a host list, use
<xref linkend='XListHosts' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XListHosts</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XListHosts'>
<funcprototype>
  <funcdef>XHostAddress *<function>XListHosts</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>int<parameter> *nhosts_return</parameter></paramdef>
  <paramdef>Bool<parameter> *state_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nhosts_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the number of hosts currently in the access control list.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>state_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the state of the access control.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XListHosts' xrefstyle='select: title'/>
function returns the current access control list as well as whether the use 
of the list at connection setup was enabled or disabled.
<xref linkend='XListHosts' xrefstyle='select: title'/>
allows a program to find out what machines can make connections.
It also returns a pointer to a list of host structures that
were allocated by the function. 
When no longer needed,
this memory should be freed by calling
<xref linkend='XFree' xrefstyle='select: title'/>.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To remove a single host, use
<xref linkend='XRemoveHost' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XRemoveHost</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XRemoveHost'>
<funcprototype>
  <funcdef><function>XRemoveHost</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>XHostAddress<parameter> *host</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Ho removed -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>host</emphasis>
    </term>
    <listitem>
      <para>
Specifies the host that is to be (Ho.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XRemoveHost' xrefstyle='select: title'/>
function removes the specified host from the access control list 
for that display.
The server must be on the same host as the client process, or a
<errorname>BadAccess</errorname>
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
</para>
<para>
<!-- .LP -->
<xref linkend='XRemoveHost' xrefstyle='select: title'/>
can generate
<errorname>BadAccess</errorname>
and
<errorname>BadValue</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To remove multiple hosts at one time, use
<xref linkend='XRemoveHosts' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XRemoveHosts</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XRemoveHosts'>
<funcprototype>
  <funcdef><function>XRemoveHosts</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>XHostAddress<parameter> *hosts</parameter></paramdef>
  <paramdef>int<parameter> num_hosts</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
<!-- .ds Ho removed -->
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>hosts</emphasis>
    </term>
    <listitem>
      <para>
Specifies each host that is to be (Ho.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>num_hosts</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of hosts.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XRemoveHosts' xrefstyle='select: title'/>
function removes each specified host from the access control list for that 
display.  
The X server must be on the same host as the client process, or a
<errorname>BadAccess</errorname>
error results.
If you remove your machine from the access list, 
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
</para>
<para>
<!-- .LP -->
<xref linkend='XRemoveHosts' xrefstyle='select: title'/>
can generate
<errorname>BadAccess</errorname>
and
<errorname>BadValue</errorname>
errors.
</para>
</sect2>
<sect2 id="Changing_Enabling_or_Disabling_Access_Control">
<title>Changing, Enabling, or Disabling Access Control</title>
<!-- .XS -->
<!-- (SN Changing, Enabling, or Disabling Access Control  -->
<!-- .XE -->
<para>
<!-- .LP -->
Xlib provides functions that you can use to enable, disable, 
or change access control.
</para>
<para>
<!-- .LP -->
For these functions to execute successfully,
the client application must reside on the same host as the X server
and/or have been given permission in the initial authorization
at connection setup.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To change access control, use
<xref linkend='XSetAccessControl' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XSetAccessControl</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XSetAccessControl'>
<funcprototype>
  <funcdef><function>XSetAccessControl</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
  <paramdef>int<parameter> mode</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>mode</emphasis>
    </term>
    <listitem>
      <para>
Specifies the mode.
You can pass
<symbol>EnableAccess</symbol>
or
<symbol>DisableAccess</symbol>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XSetAccessControl' xrefstyle='select: title'/>
function either enables or disables the use of the access control list 
at each connection setup.
</para>
<para>
<!-- .LP -->
<xref linkend='XSetAccessControl' xrefstyle='select: title'/>
can generate
<errorname>BadAccess</errorname>
and
<errorname>BadValue</errorname>
errors.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To enable access control, use
<xref linkend='XEnableAccessControl' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XEnableAccessControl</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XEnableAccessControl'>
<funcprototype>
  <funcdef><function>XEnableAccessControl</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XEnableAccessControl' xrefstyle='select: title'/>
function enables the use of the access control list at each connection setup.
</para>
<para>
<!-- .LP -->
<xref linkend='XEnableAccessControl' xrefstyle='select: title'/>
can generate a
<errorname>BadAccess</errorname>
error.
</para>
<para>
<!-- .LP -->
<!-- .sp -->
To disable access control, use
<xref linkend='XDisableAccessControl' xrefstyle='select: title'/>.
</para>
<indexterm significance="preferred"><primary>XDisableAccessControl</primary></indexterm>
<!-- .sM -->
<funcsynopsis id='XDisableAccessControl'>
<funcprototype>
  <funcdef><function>XDisableAccessControl</function></funcdef>
  <paramdef>Display<parameter> *display</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<!-- .FN -->
<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the connection to the X server.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
<para>
<!-- .LP -->
<!-- .eM -->
The
<xref linkend='XDisableAccessControl' xrefstyle='select: title'/>
function disables the use of the access control list at each connection setup.
</para>
<para>
<!-- .LP -->
<xref linkend='XDisableAccessControl' xrefstyle='select: title'/>
can generate a
<errorname>BadAccess</errorname>
error.
<!-- .bp -->

</para>
</sect2>
</sect1>
</chapter>
