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571 lines
20 KiB
XML
571 lines
20 KiB
XML
<part>
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<title>GIO Overview</title>
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<chapter>
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<title>Introduction</title>
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<para>
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GIO is striving to provide a modern, easy-to-use VFS API that sits
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at the right level in the library stack. The goal is to overcome the
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shortcomings of GnomeVFS and provide an API that is so good that
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developers prefer it over raw POSIX calls. Among other things
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that means using GObject. It also means not cloning the POSIX
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API, but providing higher-level, document-centric interfaces.
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</para>
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<para>
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The abstract file system model of GIO consists of a number of
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interfaces and base classes for I/O and files:
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<variablelist>
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<varlistentry>
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<term>GFile</term>
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<listitem><para>reference to a file</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GFileInfo</term>
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<listitem><para>information about a file or filesystem</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GFileEnumerator</term>
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<listitem><para>list files in directories</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GDrive</term>
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<listitem><para>represents a drive</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GVolume</term>
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<listitem><para>represents a file system in an abstract way</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GMount</term>
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<listitem><para>represents a mounted file system</para></listitem>
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</varlistentry>
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</variablelist>
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Then there is a number of stream classes, similar to the input and
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output stream hierarchies that can be found in frameworks like Java:
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<variablelist>
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<varlistentry>
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<term>GInputStream</term>
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<listitem><para>read data</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GOutputStream</term>
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<listitem><para>write data</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GIOStream</term>
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<listitem><para>read and write data</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GSeekable</term>
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<listitem><para>interface optionally implemented by streams to support seeking</para></listitem>
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</varlistentry>
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</variablelist>
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There are interfaces related to applications and the types
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of files they handle:
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<variablelist>
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<varlistentry>
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<term>GAppInfo</term>
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<listitem><para>information about an installed application</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GIcon</term>
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<listitem><para>abstract type for file and application icons</para></listitem>
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</varlistentry>
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</variablelist>
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There is a framework for storing and retrieving application settings:
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<variablelist>
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<varlistentry>
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<term>GSettings</term>
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<listitem><para>stores and retrieves application settings</para></listitem>
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</varlistentry>
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</variablelist>
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There is support for network programming, including name resolution, lowlevel socket
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APIs and highlevel client and server helper classes:
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<variablelist>
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<varlistentry>
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<term>GSocket</term>
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<listitem><para>lowlevel platform independent socket object</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GResolver</term>
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<listitem><para>asynchronous and cancellable DNS resolver</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GSocketClient</term>
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<listitem><para>high-level network client helper</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GSocketService</term>
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<listitem><para>high-level network server helper</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GSocketConnection</term>
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<listitem><para>network connection stream</para></listitem>
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</varlistentry>
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</variablelist>
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There is support for connecting to <link linkend="http://www.freedesktop.org/wiki/Software/dbus">D-Bus</link>,
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sending and receiving messages, owning and watching bus names,
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and making objects available on the bus:
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<variablelist>
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<varlistentry>
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<term>GDBusConnection</term>
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<listitem><para>a D-Bus connection</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GDBusMethodInvocation</term>
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<listitem><para>for handling remove calls</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GDBusServer</term>
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<listitem><para>helper for accepting connections</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>GDBusProxy</term>
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<listitem><para>proxy to access D-Bus interfaces on a remote object</para></listitem>
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</varlistentry>
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</variablelist>
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Beyond these, GIO provides facilities for file monitoring,
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asynchronous I/O and filename completion. In addition to the
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interfaces, GIO provides implementations for the local case.
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Implementations for various network file systems are provided
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by the GVFS package as loadable modules.
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</para>
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<para>
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Other design choices which consciously break with the GnomeVFS
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design are to move backends out-of-process, which minimizes the
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dependency bloat and makes the whole system more robust. The backends
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are not included in GIO, but in the separate GVFS package. The GVFS
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package also contains the GVFS daemon, which spawn further mount
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daemons for each individual connection.
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</para>
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<figure id="gvfs-overview">
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<title>GIO in the GTK+ library stack</title>
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<graphic fileref="gvfs-overview.png" format="PNG"></graphic>
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</figure>
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<para>
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The GIO model of I/O is stateful: if an application establishes e.g.
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a SFTP connection to a server, it becomes available to all applications
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in the session; the user does not have to enter his password over
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and over again.
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</para>
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<para>
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One of the big advantages of putting the VFS in the GLib layer
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is that GTK+ can directly use it, e.g. in the filechooser.
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</para>
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</chapter>
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<chapter>
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<title>Compiling GIO applications</title>
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<para>
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GIO comes with a <filename>gio-2.0.pc</filename> file that you
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should use together with <literal>pkg-config</literal> to obtain
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the necessary information about header files and libraries. See
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the <literal>pkg-config</literal> man page or the GLib documentation
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for more information on how to use <literal>pkg-config</literal>
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to compile your application.
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</para>
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<para>
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If you are using GIO on UNIX-like systems, you may want to use
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UNIX-specific GIO interfaces such as #GUnixInputStream,
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#GUnixOutputStream, #GUnixMount or #GDesktopAppInfo.
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To do so, use the <filename>gio-unix-2.0.pc</filename> file
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instead of <filename>gio-2.0.pc</filename>
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</para>
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<para>
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Since GIO is based on GObject, you need to call g_type_init()
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before you can use any GIO functions. If your application uses
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GTK+, this is already taken care of by gtk_init().
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</para>
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</chapter>
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<chapter>
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<title>Running GIO applications</title>
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<para>
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GIO inspects a few of environment variables in addition to the
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ones used by GLib.
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</para>
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<formalpara>
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<title><envar>XDG_DATA_HOME</envar>, <envar>XDG_DATA_DIRS</envar></title>
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<para>
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GIO uses these environment variables to locate MIME information.
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For more information, see the <ulink url="http://freedesktop.org/Standards/shared-mime-info-spec">Shared MIME-info Database</ulink>
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and the <ulink url="http://freedesktop.org/Standards/basedir-spec">Base Directory Specification</ulink>.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GVFS_DISABLE_FUSE</envar></title>
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<para>
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This variable can be set to keep #Gvfs from starting the fuse backend,
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which may be unwanted or unnecessary in certain situations.
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</para>
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</formalpara>
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<para>
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The following environment variables are only useful for debugging
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GIO itself or modules that it loads. They should not be set in a
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production environment.
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</para>
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<formalpara>
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<title><envar>GIO_USE_VFS</envar></title>
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<para>
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This environment variable can be set to the name of a #GVfs
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implementation to override the default for debugging purposes.
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The #GVfs implementation for local files that is included in GIO
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has the name "local", the implementation in the gvfs module has
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the name "gvfs".
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GIO_USE_VOLUME_MONITOR</envar></title>
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<para>
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This variable can be set to the name of a #GVolumeMonitor
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implementation to override the default for debugging purposes.
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The #GVolumeMonitor implementation for local files that is included
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in GIO has the name "unix", the hal-based implementation in the
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gvfs module has the name "hal".
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GIO_USE_URI_ASSOCIATION</envar></title>
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<para>
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This variable can be set to the name of a #GDesktopAppInfoLookup
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implementation to override the default for debugging purposes.
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GIO does not include a #GDesktopAppInfoLookup implementation,
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the GConf-based implementation in the gvfs module has the name
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"gconf".
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GVFS_INOTIFY_DIAG</envar></title>
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<para>
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When this environment variable is set and GIO has been built
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with inotify support, a dump of diagnostic inotify information
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will be written every 20 seconds to a file named
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<filename>/tmp/gvfsdid.<replaceable>pid</replaceable></filename>.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GIO_EXTRA_MODULES</envar></title>
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<para>
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When this environment variable is set to a path, or a set of
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paths separated by a colon, GIO will attempt to load
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modules from within the path.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GSETTINGS_BACKEND</envar></title>
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<para>
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This variable can be set to the name of a #GSettingsBackend
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implementation to override the default for debugging purposes.
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The memory-based implementation that is included in GIO has
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the name "memory", the one in dconf has the name "dconf-settings".
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</para>
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</formalpara>
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<formalpara>
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<title><envar>GSETTINGS_SCHEMA_DIR</envar></title>
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<para>
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This variable can be set to the name of a directory that is
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considered in addition to the <filename>glib-2.0/schemas</filename>
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subdirectories of the XDG system data dirs when looking
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for compiled schemas for #GSettings.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>DBUS_SYSTEM_BUS_ADDRESS</envar></title>
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<para>
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This variable is consulted to find the address of the D-Bus system
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bus. For the format of D-Bus addresses, see the D-Bus
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<ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#addresses">specification</ulink>.
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</para>
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<para>
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Setting this variable overrides platform-specific ways of determining
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the system bus address.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>DBUS_SESSION_BUS_ADDRESS</envar></title>
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<para>
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This variable is consulted to find the address of the D-Bus session bus.
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</para>
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<para>
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Setting this variable overrides platform-specific ways of determining
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the session bus address.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>DBUS_STARTER_BUS_TYPE</envar></title>
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<para>
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This variable is consulted to find out the 'starter' bus for an
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application that has been started via D-Bus activation. The possible
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values are 'system' or 'session'.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>G_DBUS_DEBUG</envar></title>
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<para>
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This variable can be set to a list of debug options, which
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cause GLib to print out different types of debugging
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information when using the D-Bus routines.
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<variablelist>
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<varlistentry>
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<term>transport</term>
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<listitem><para>Show IO activity (e.g. reads and writes)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>message</term>
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<listitem><para>Show all sent and received D-Bus messages</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>payload</term>
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<listitem><para>Show payload for all sent and received D-Bus messages (implies message)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>call</term>
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<listitem><para>Trace g_dbus_connection_call() and g_dbus_connection_call_sync() API usage</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>signal</term>
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<listitem><para>Show when a D-Bus signal is received</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>incoming</term>
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<listitem><para>Show when an incoming D-Bus method call is received</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>return</term>
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<listitem><para>Show when a reply is returned via the #GDBusMethodInvocation API</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>emission</term>
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<listitem><para>Trace g_dbus_connection_emit_signal() API usage</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>authentication</term>
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<listitem><para>Show information about connection authentication</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>address</term>
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<listitem><para>Show information about D-Bus address lookups and autolaunching</para></listitem>
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</varlistentry>
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</variablelist>
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The special value <literal>all</literal> can be used to turn
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on all debug options. The special value
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<literal>help</literal> can be used to print a list of
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supported options to standard output.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR</envar></title>
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<para>
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Can be used to override the directory used to store the
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keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
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authentication mechanism. Normally the directory used is
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<filename>.dbus-keyrings</filename> in the user's home
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directory.
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</para>
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</formalpara>
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<formalpara>
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<title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION</envar></title>
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<para>
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If set, the permissions of the directory used to store the
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keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
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authentication mechanism won't be checked. Normally the
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directory must be readable only by the user.
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</para>
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</formalpara>
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</chapter>
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<chapter id="extending-gio">
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<title>Extending GIO</title>
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<para>
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A lot of the functionality that is accessible through GIO
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is implemented in loadable modules, and modules provide a convenient
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way to extend GIO. In addition to the #GIOModule API which supports
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writing such modules, GIO has a mechanism to define extension points,
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and register implementations thereof, see #GIOExtensionPoint.
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</para>
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<para>
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The following extension points are currently defined by GIO:
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</para>
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<formalpara>
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<title>G_VFS_EXTENSION_POINT_NAME</title>
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<para>
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Allows to override the functionality of the #GVfs class.
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Implementations of this extension point must be derived from #GVfs.
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GIO uses the implementation with the highest priority that is active,
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see g_vfs_is_active().
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</para>
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<para>
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GIO implements this extension point for local files, gvfs contains
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an implementation that supports all the backends in gvfs.
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</para>
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</formalpara>
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<formalpara>
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<title>G_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
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<para>
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Allows to add more volume monitors.
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Implementations of this extension point must be derived from
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#GVolumeMonitor. GIO uses all registered extensions.
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</para>
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<para>
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gvfs contains an implementation that works together with the #GVfs
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implementation in gvfs.
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</para>
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</formalpara>
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<formalpara>
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<title>G_NATIVE_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
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<para>
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Allows to override the 'native' volume monitor.
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Implementations of this extension point must be derived from
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#GNativeVolumeMonitor. GIO uses the implementation with
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the highest priority that is supported, as determined by the
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is_supported() vfunc in #GVolumeMonitorClass.
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</para>
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<para>
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GIO implements this extension point for local mounts,
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gvfs contains a hal-based implementation.
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</para>
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</formalpara>
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<formalpara>
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<title>G_LOCAL_FILE_MONITOR_EXTENSION_POINT_NAME</title>
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<para>
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Allows to override the file monitor implementation for
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local files. Implementations of this extension point must
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be derived from #GLocalFileMonitor. GIO uses the implementation
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with the highest priority that is supported, as determined by the
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is_supported() vfunc in #GLocalFileMonitorClass.
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</para>
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<para>
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GIO uses this extension point internally, to switch between
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its fam-based and inotify-based file monitoring implementations.
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</para>
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</formalpara>
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<formalpara>
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<title>G_LOCAL_DIRECTORY_MONITOR_EXTENSION_POINT_NAME</title>
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<para>
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Allows to override the directory monitor implementation for
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local files. Implementations of this extension point must be
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derived from #GLocalDirectoryMonitor. GIO uses the implementation
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with the highest priority that is supported, as determined by the
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is_supported() vfunc in #GLocalDirectoryMonitorClass.
|
|
</para>
|
|
<para>
|
|
GIO uses this extension point internally, to switch between
|
|
its fam-based and inotify-based directory monitoring implementations.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<formalpara>
|
|
<title>G_DESKTOP_APP_INFO_LOOKUP_EXTENSION_POINT_NAME</title>
|
|
|
|
<para>
|
|
Unix-only. Allows to provide a way to associate default handlers
|
|
with URI schemes. Implementations of this extension point must
|
|
implement the #GDesktopAppInfoLookup interface. GIO uses the
|
|
implementation with the highest priority.
|
|
</para>
|
|
<para>
|
|
This extension point has been discontinued in GLib 2.28. It is
|
|
still available to keep API and ABI stability, but GIO is no
|
|
longer using it for default handlers. Instead, the mime handler
|
|
mechanism is used, together with x-scheme-handler pseudo-mimetypes.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<formalpara>
|
|
<title>G_SETTINGS_BACKEND_EXTENSION_POINT_NAME</title>
|
|
|
|
<para>
|
|
Allows to provide an alternative storage for #GSettings.
|
|
Implementations of this extension point must derive from the
|
|
#GSettingsBackend type. GIO contains a keyfile-based
|
|
implementation of this extension point, another one is provided
|
|
by dconf.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<formalpara>
|
|
<title>G_PROXY_EXTENSION_POINT_NAME</title>
|
|
|
|
<para>
|
|
Allows to provide implementations for network proxying.
|
|
Implementations of this extension point must provide the
|
|
#GProxy interface, and must be named after the network
|
|
protocol they are proxying.
|
|
</para>
|
|
<para>
|
|
glib-networking contains an implementation of this extension
|
|
point based on libproxy.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<formalpara>
|
|
<title>G_TLS_BACKEND_EXTENSION_POINT_NAME</title>
|
|
|
|
<para>
|
|
Allows to provide implementations for TLS support.
|
|
Implementations of this extension point must implement
|
|
the #GTlsBackend interface.
|
|
</para>
|
|
<para>
|
|
glib-networking contains an implementation of this extension
|
|
point.
|
|
</para>
|
|
</formalpara>
|
|
|
|
</chapter>
|
|
</part>
|