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>
187 Since GIO is based on GObject, you need to call g_type_init()
188 before you can use any GIO functions. If your application uses
189 GTK+, this is already taken care of by gtk_init().
194 <title>Running GIO applications</title>
197 GIO inspects a few of environment variables in addition to the
202 <title><envar>XDG_DATA_HOME</envar>, <envar>XDG_DATA_DIRS</envar></title>
205 GIO uses these environment variables to locate MIME information.
206 For more information, see the <ulink url="http://freedesktop.org/Standards/shared-mime-info-spec">Shared MIME-info Database</ulink>
207 and the <ulink url="http://freedesktop.org/Standards/basedir-spec">Base Directory Specification</ulink>.
212 <title><envar>GVFS_DISABLE_FUSE</envar></title>
215 This variable can be set to keep #Gvfs from starting the fuse backend,
216 which may be unwanted or unnecessary in certain situations.
221 The following environment variables are only useful for debugging
222 GIO itself or modules that it loads. They should not be set in a
223 production environment.
226 <title><envar>GIO_USE_VFS</envar></title>
229 This environment variable can be set to the name of a #GVfs
230 implementation to override the default for debugging purposes.
231 The #GVfs implementation for local files that is included in GIO
232 has the name "local", the implementation in the gvfs module has
238 <title><envar>GIO_USE_VOLUME_MONITOR</envar></title>
241 This variable can be set to the name of a #GVolumeMonitor
242 implementation to override the default for debugging purposes.
243 The #GVolumeMonitor implementation for local files that is included
244 in GIO has the name "unix", the hal-based implementation in the
245 gvfs module has the name "hal".
250 <title><envar>GIO_USE_URI_ASSOCIATION</envar></title>
253 This variable can be set to the name of a #GDesktopAppInfoLookup
254 implementation to override the default for debugging purposes.
255 GIO does not include a #GDesktopAppInfoLookup implementation,
256 the GConf-based implementation in the gvfs module has the name
262 <title><envar>GVFS_INOTIFY_DIAG</envar></title>
265 When this environment variable is set and GIO has been built
266 with inotify support, a dump of diagnostic inotify information
267 will be written every 20 seconds to a file named
268 <filename>/tmp/gvfsdid.<replaceable>pid</replaceable></filename>.
273 <title><envar>GIO_EXTRA_MODULES</envar></title>
276 When this environment variable is set to a path, or a set of
277 paths separated by a colon, GIO will attempt to load
278 modules from within the path.
283 <title><envar>GSETTINGS_BACKEND</envar></title>
286 This variable can be set to the name of a #GSettingsBackend
287 implementation to override the default for debugging purposes.
288 The memory-based implementation that is included in GIO has
289 the name "memory", the one in dconf has the name "dconf-settings".
294 <title><envar>GSETTINGS_SCHEMA_DIR</envar></title>
297 This variable can be set to the name of a directory that is
298 considered in addition to the <filename>glib-2.0/schemas</filename>
299 subdirectories of the XDG system data dirs when looking
300 for compiled schemas for #GSettings.
305 <title><envar>DBUS_SYSTEM_BUS_ADDRESS</envar></title>
308 This variable is consulted to find the address of the D-Bus system
309 bus. For the format of D-Bus addresses, see the D-Bus
310 <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#addresses">specification</ulink>.
313 Setting this variable overrides platform-specific ways of determining
314 the system bus address.
319 <title><envar>DBUS_SESSION_BUS_ADDRESS</envar></title>
322 This variable is consulted to find the address of the D-Bus session bus.
325 Setting this variable overrides platform-specific ways of determining
326 the session bus address.
331 <title><envar>DBUS_STARTER_BUS_TYPE</envar></title>
334 This variable is consulted to find out the 'starter' bus for an
335 application that has been started via D-Bus activation. The possible
336 values are 'system' or 'session'.
341 <title><envar>G_DBUS_DEBUG</envar></title>
344 This variable can be set to a list of debug options, which
345 cause GLib to print out different types of debugging
346 information when using the D-Bus routines.
349 <term>transport</term>
350 <listitem><para>Show IO activity (e.g. reads and writes)</para></listitem>
354 <listitem><para>Show all sent and received D-Bus messages</para></listitem>
358 <listitem><para>Show payload for all sent and received D-Bus messages (implies message)</para></listitem>
362 <listitem><para>Trace g_dbus_connection_call() and g_dbus_connection_call_sync() API usage</para></listitem>
366 <listitem><para>Show when a D-Bus signal is received</para></listitem>
369 <term>incoming</term>
370 <listitem><para>Show when an incoming D-Bus method call is received</para></listitem>
374 <listitem><para>Show when a reply is returned via the #GDBusMethodInvocation API</para></listitem>
377 <term>emission</term>
378 <listitem><para>Trace g_dbus_connection_emit_signal() API usage</para></listitem>
381 <term>authentication</term>
382 <listitem><para>Show information about connection authentication</para></listitem>
386 <listitem><para>Show information about D-Bus address lookups and autolaunching</para></listitem>
389 The special value <literal>all</literal> can be used to turn
390 on all debug options. The special value
391 <literal>help</literal> can be used to print a list of
392 supported options to standard output.
397 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR</envar></title>
400 Can be used to override the directory used to store the
401 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
402 authentication mechanism. Normally the directory used is
403 <filename>.dbus-keyrings</filename> in the user's home
409 <title><envar>G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION</envar></title>
412 If set, the permissions of the directory used to store the
413 keyring used in the <literal>DBUS_COOKIE_SHA1</literal>
414 authentication mechanism won't be checked. Normally the
415 directory must be readable only by the user.
420 <chapter id="extending-gio">
421 <title>Extending GIO</title>
424 A lot of the functionality that is accessible through GIO
425 is implemented in loadable modules, and modules provide a convenient
426 way to extend GIO. In addition to the #GIOModule API which supports
427 writing such modules, GIO has a mechanism to define extension points,
428 and register implementations thereof, see #GIOExtensionPoint.
431 The following extension points are currently defined by GIO:
435 <title>G_VFS_EXTENSION_POINT_NAME</title>
438 Allows to override the functionality of the #GVfs class.
439 Implementations of this extension point must be derived from #GVfs.
440 GIO uses the implementation with the highest priority that is active,
441 see g_vfs_is_active().
444 GIO implements this extension point for local files, gvfs contains
445 an implementation that supports all the backends in gvfs.
450 <title>G_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
453 Allows to add more volume monitors.
454 Implementations of this extension point must be derived from
455 #GVolumeMonitor. GIO uses all registered extensions.
458 gvfs contains an implementation that works together with the #GVfs
459 implementation in gvfs.
464 <title>G_NATIVE_VOLUME_MONITOR_EXTENSION_POINT_NAME</title>
467 Allows to override the 'native' volume monitor.
468 Implementations of this extension point must be derived from
469 #GNativeVolumeMonitor. GIO uses the implementation with
470 the highest priority that is supported, as determined by the
471 is_supported() vfunc in #GVolumeMonitorClass.
474 GIO implements this extension point for local mounts,
475 gvfs contains a hal-based implementation.
480 <title>G_LOCAL_FILE_MONITOR_EXTENSION_POINT_NAME</title>
483 Allows to override the file monitor implementation for
484 local files. Implementations of this extension point must
485 be derived from #GLocalFileMonitor. GIO uses the implementation
486 with the highest priority that is supported, as determined by the
487 is_supported() vfunc in #GLocalFileMonitorClass.
490 GIO uses this extension point internally, to switch between
491 its fam-based and inotify-based file monitoring implementations.
496 <title>G_LOCAL_DIRECTORY_MONITOR_EXTENSION_POINT_NAME</title>
499 Allows to override the directory monitor implementation for
500 local files. Implementations of this extension point must be
501 derived from #GLocalDirectoryMonitor. GIO uses the implementation
502 with the highest priority that is supported, as determined by the
503 is_supported() vfunc in #GLocalDirectoryMonitorClass.
506 GIO uses this extension point internally, to switch between
507 its fam-based and inotify-based directory monitoring implementations.
512 <title>G_DESKTOP_APP_INFO_LOOKUP_EXTENSION_POINT_NAME</title>
515 Unix-only. Allows to provide a way to associate default handlers
516 with URI schemes. Implementations of this extension point must
517 implement the #GDesktopAppInfoLookup interface. GIO uses the
518 implementation with the highest priority.
521 This extension point has been discontinued in GLib 2.28. It is
522 still available to keep API and ABI stability, but GIO is no
523 longer using to for default handlers. Instead, the mime handler
524 mechanism is used, together with x-scheme-handler pseudo-mimetypes.
529 <title>G_SETTINGS_BACKEND_EXTENSION_POINT_NAME</title>
532 Allows to provide an alternative storage for #GSettings.
533 Implementations of this extension point must derive from the
534 #GSettingsBackend type. GIO contains a keyfile-based
535 implementation of this extension point, another one is provided
541 <title>G_PROXY_EXTENSION_POINT_NAME</title>
544 Allows to provide implementations for network proxying.
545 Implementations of this extension point must provide the
546 #GProxy interface, and must be named after the network
547 protocol they are proxying.
550 glib-networking contains an implementation of this extension
551 point based on libproxy.
556 <title>G_TLS_BACKEND_EXTENSION_POINT_NAME</title>
559 Allows to provide implementations for TLS support.
560 Implementations of this extension point must implement
561 the #GTlsBackend interface.
564 glib-networking contains an implementation of this extension