2 <title>GIO Overview</title>
5 <title>Introduction</title>
8 GIO is striving to provide a modern, easy-to-use VFS API that sits
9 at the right level in the library stack. The goal is to overcome the
10 shortcomings of GnomeVFS and provide an API that is so good that
11 developers prefer it over raw POSIX calls. Among other things
12 that means using GObject. It also means not cloning the POSIX
13 API, but providing higher-level, document-centric interfaces.
17 The abstract file system model of GIO consists of a number of
18 interfaces and base classes for I/O and files:
22 <listitem><para>reference to a file</para></listitem>
25 <term>GFileInfo</term>
26 <listitem><para>information about a file or filesystem</para></listitem>
29 <term>GFileEnumerator</term>
30 <listitem><para>list files in directories</para></listitem>
34 <listitem><para>represents a drive</para></listitem>
38 <listitem><para>represents a file system in an abstract way</para></listitem>
42 <listitem><para>represents a mounted file system</para></listitem>
45 Then there is a number of stream classes, similar to the input and
46 output stream hierarchies that can be found in frameworks like Java:
49 <term>GInputStream</term>
50 <listitem><para>read data</para></listitem>
53 <term>GOutputStream</term>
54 <listitem><para>write data</para></listitem>
57 <term>GIOStream</term>
58 <listitem><para>read and write data</para></listitem>
61 <term>GSeekable</term>
62 <listitem><para>interface optionally implemented by streams to support seeking</para></listitem>
65 There are interfaces related to applications and the types
70 <listitem><para>information about an installed application</para></listitem>
74 <listitem><para>abstract type for file and application icons</para></listitem>
77 There is a framework for storing and retrieving application settings:
80 <term>GSettings</term>
81 <listitem><para>stores and retrieves application settings</para></listitem>
84 There is support for network programming, including name resolution, lowlevel socket
85 APIs and highlevel client and server helper classes:
89 <listitem><para>lowlevel platform independent socket object</para></listitem>
92 <term>GResolver</term>
93 <listitem><para>asynchronous and cancellable DNS resolver</para></listitem>
96 <term>GSocketClient</term>
97 <listitem><para>high-level network client helper</para></listitem>
100 <term>GSocketService</term>
101 <listitem><para>high-level network server helper</para></listitem>
104 <term>GSocketConnection</term>
105 <listitem><para>network connection stream</para></listitem>
108 There is support for connecting to <link linkend="http://www.freedesktop.org/wiki/Software/dbus">D-Bus</link>,
109 sending and receiving messages, owning and watching bus names,
110 and making objects available on the bus:
113 <term>GDBusConnection</term>
114 <listitem><para>a D-Bus connection</para></listitem>
118 <term>GDBusMethodInvocation</term>
119 <listitem><para>for handling remove calls</para></listitem>
123 <term>GDBusServer</term>
124 <listitem><para>helper for accepting connections</para></listitem>
128 <term>GDBusProxy</term>
129 <listitem><para>proxy to access D-Bus interfaces on a remote object</para></listitem>
133 Beyond these, GIO provides facilities for file monitoring,
134 asynchronous I/O and filename completion. In addition to the
135 interfaces, GIO provides implementations for the local case.
136 Implementations for various network file systems are provided
137 by the GVFS package as loadable modules.
141 Other design choices which consciously break with the GnomeVFS
142 design are to move backends out-of-process, which minimizes the
143 dependency bloat and makes the whole system more robust. The backends
144 are not included in GIO, but in the separate GVFS package. The GVFS
145 package also contains the GVFS daemon, which spawn further mount
146 daemons for each individual connection.
149 <figure id="gvfs-overview">
150 <title>GIO in the GTK+ library stack</title>
151 <graphic fileref="gvfs-overview.png" format="PNG"></graphic>
155 The GIO model of I/O is stateful: if an application establishes e.g.
156 a SFTP connection to a server, it becomes available to all applications
157 in the session; the user does not have to enter his password over
161 One of the big advantages of putting the VFS in the GLib layer
162 is that GTK+ can directly use it, e.g. in the filechooser.
167 <title>Compiling GIO applications</title>
170 GIO comes with a <filename>gio-2.0.pc</filename> file that you
171 should use together with <literal>pkg-config</literal> to obtain
172 the necessary information about header files and libraries. See
173 the <literal>pkg-config</literal> man page or the GLib documentation
174 for more information on how to use <literal>pkg-config</literal>
175 to compile your application.
179 If you are using GIO on UNIX-like systems, you may want to use
180 UNIX-specific GIO interfaces such as #GUnixInputStream,
181 #GUnixOutputStream, #GUnixMount or #GDesktopAppInfo.
182 To do so, use the <filename>gio-unix-2.0.pc</filename> file
183 instead of <filename>gio-2.0.pc</filename>
188 <title>Running GIO applications</title>
191 GIO inspects a few of environment variables in addition to the
196 <title><envar>XDG_DATA_HOME</envar>, <envar>XDG_DATA_DIRS</envar></title>
199 GIO uses these environment variables to locate MIME information.
200 For more information, see the <ulink url="http://freedesktop.org/Standards/shared-mime-info-spec">Shared MIME-info Database</ulink>
201 and the <ulink url="http://freedesktop.org/Standards/basedir-spec">Base Directory Specification</ulink>.
206 <title><envar>GVFS_DISABLE_FUSE</envar></title>
209 This variable can be set to keep #Gvfs from starting the fuse backend,
210 which may be unwanted or unnecessary in certain situations.
215 The following environment variables are only useful for debugging
216 GIO itself or modules that it loads. They should not be set in a
217 production environment.
220 <title><envar>GIO_USE_VFS</envar></title>
223 This environment variable can be set to the name of a #GVfs
224 implementation to override the default for debugging purposes.
225 The #GVfs implementation for local files that is included in GIO
226 has the name "local", the implementation in the gvfs module has
232 <title><envar>GIO_USE_VOLUME_MONITOR</envar></title>
235 This variable can be set to the name of a #GVolumeMonitor
236 implementation to override the default for debugging purposes.
237 The #GVolumeMonitor implementation for local files that is included
238 in GIO has the name "unix", the hal-based implementation in the
239 gvfs module has the name "hal".
244 <title><envar>GIO_USE_URI_ASSOCIATION</envar></title>
247 This variable can be set to the name of a #GDesktopAppInfoLookup
248 implementation to override the default for debugging purposes.
249 GIO does not include a #GDesktopAppInfoLookup implementation,
250 the GConf-based implementation in the gvfs module has the name
256 <title><envar>GVFS_INOTIFY_DIAG</envar></title>
259 When this environment variable is set and GIO has been built
260 with inotify support, a dump of diagnostic inotify information
261 will be written every 20 seconds to a file named
262 <filename>/tmp/gvfsdid.<replaceable>pid</replaceable></filename>.
267 <title><envar>GIO_EXTRA_MODULES</envar></title>
270 When this environment variable is set to a path, or a set of
271 paths separated by a colon, GIO will attempt to load
272 modules from within the path.
277 <title><envar>GSETTINGS_BACKEND</envar></title>
280 This variable can be set to the name of a #GSettingsBackend
281 implementation to override the default for debugging purposes.
282 The memory-based implementation that is included in GIO has
283 the name "memory", the one in dconf has the name "dconf-settings".
288 <title><envar>GSETTINGS_SCHEMA_DIR</envar></title>
291 This variable can be set to the name of a directory that is
292 considered in addition to the <filename>glib-2.0/schemas</filename>
293 subdirectories of the XDG system data dirs when looking
294 for compiled schemas for #GSettings.
299 <title><envar>DBUS_SYSTEM_BUS_ADDRESS</envar></title>
302 This variable is consulted to find the address of the D-Bus system
303 bus. For the format of D-Bus addresses, see the D-Bus
304 <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#addresses">specification</ulink>.
307 Setting this variable overrides platform-specific ways of determining
308 the system bus address.
313 <title><envar>DBUS_SESSION_BUS_ADDRESS</envar></title>
316 This variable is consulted to find the address of the D-Bus session bus.
319 Setting this variable overrides platform-specific ways of determining
320 the session bus address.
325 <title><envar>DBUS_STARTER_BUS_TYPE</envar></title>
328 This variable is consulted to find out the 'starter' bus for an
329 application that has been started via D-Bus activation. The possible
330 values are 'system' or 'session'.
335 <title><envar>G_DBUS_DEBUG</envar></title>
338 This variable can be set to a list of debug options, which
339 cause GLib to print out different types of debugging
340 information when using the D-Bus routines.
344 <listitem><para>Show all sent and received D-Bus messages</para></listitem>
348 <listitem><para>Show payload for all sent and received D-Bus messages (implies message)</para></listitem>
352 <listitem><para>Trace g_dbus_connection_call() and g_dbus_connection_call_sync() API usage</para></listitem>
356 <listitem><para>Show when a D-Bus signal is received</para></listitem>
359 <term>incoming</term>
360 <listitem><para>Show when an incoming D-Bus method call is received</para></listitem>
364 <listitem><para>Show when a reply is returned via the #GDBusMethodInvocation API</para></listitem>
367 <term>emission</term>
368 <listitem><para>Trace g_dbus_connection_emit_signal() API usage</para></listitem>
371 <term>authentication</term>
372 <listitem><para>Show information about connection authentication</para></listitem>
376 <listitem><para>Show information about D-Bus address lookups and autolaunching</para></listitem>
379 The special value <literal>all</literal> can be used to turn
380 on all debug options. The special value
381 <literal>help</literal> can be used to print a list of
382 supported options to standard output.
387 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR</envar></title>
390 Can be used to override the directory used to store the
391 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
392 authentication mechanism. Normally the directory used is
393 <filename>.dbus-keyrings</filename> in the user's home
399 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION</envar></title>
402 If set, the permissions of the directory used to store the
403 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
404 authentication mechanism won't be checked. Normally the
405 directory must be readable only by the user.
410 <chapter id="extending-gio">
411 <title>Extending GIO</title>
414 A lot of the functionality that is accessible through GIO
415 is implemented in loadable modules, and modules provide a convenient
416 way to extend GIO. In addition to the #GIOModule API which supports
417 writing such modules, GIO has a mechanism to define extension points,
418 and register implementations thereof, see #GIOExtensionPoint.
421 The following extension points are currently defined by GIO:
425 <title>G_VFS_EXTENSION_POINT_NAME</title>
428 Allows to override the functionality of the #GVfs class.
429 Implementations of this extension point must be derived from #GVfs.
430 GIO uses the implementation with the highest priority that is active,
431 see g_vfs_is_active().
434 GIO implements this extension point for local files, gvfs contains
435 an implementation that supports all the backends in gvfs.
440 <title>G_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
443 Allows to add more volume monitors.
444 Implementations of this extension point must be derived from
445 #GVolumeMonitor. GIO uses all registered extensions.
448 gvfs contains an implementation that works together with the #GVfs
449 implementation in gvfs.
454 <title>G_NATIVE_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
457 Allows to override the 'native' volume monitor.
458 Implementations of this extension point must be derived from
459 #GNativeVolumeMonitor. GIO uses the implementation with
460 the highest priority that is supported, as determined by the
461 is_supported() vfunc in #GVolumeMonitorClass.
464 GIO implements this extension point for local mounts,
465 gvfs contains a hal-based implementation.
470 <title>G_LOCAL_FILE_MONITOR_EXTENSION_POINT_NAME</title>
473 Allows to override the file monitor implementation for
474 local files. Implementations of this extension point must
475 be derived from #GLocalFileMonitor. GIO uses the implementation
476 with the highest priority that is supported, as determined by the
477 is_supported() vfunc in #GLocalFileMonitorClass.
480 GIO uses this extension point internally, to switch between
481 its fam-based and inotify-based file monitoring implementations.
486 <title>G_LOCAL_DIRECTORY_MONITOR_EXTENSION_POINT_NAME</title>
489 Allows to override the directory monitor implementation for
490 local files. Implementations of this extension point must be
491 derived from #GLocalDirectoryMonitor. GIO uses the implementation
492 with the highest priority that is supported, as determined by the
493 is_supported() vfunc in #GLocalDirectoryMonitorClass.
496 GIO uses this extension point internally, to switch between
497 its fam-based and inotify-based directory monitoring implementations.
502 <title>G_DESKTOP_APP_INFO_LOOKUP_EXTENSION_POINT_NAME</title>
505 Unix-only. Allows to provide a way to associate default handlers
506 with URI schemes. Implementations of this extension point must
507 implement the #GDesktopAppInfoLookup interface. GIO uses the
508 implementation with the highest priority.
511 gvfs contains a GConf-based implementation that uses the
512 same GConf keys as gnome-vfs.
517 <title>G_SETTINGS_BACKEND_EXTENSION_POINT_NAME</title>
520 Allows to provide an alternative storage for #GSettings.
521 Implementations of this extension point must derive from the
522 #GSettingsBackend type. GIO contains a keyfile-based
523 implementation of this extension point, another one is provided