mirror of
https://gitlab.gnome.org/GNOME/glib.git
synced 2024-11-11 03:46:17 +01:00
444 lines
19 KiB
XML
444 lines
19 KiB
XML
<part id="migrating">
|
|
<title>Migrating to GIO</title>
|
|
|
|
<chapter>
|
|
<title>Migrating from POSIX to GIO</title>
|
|
|
|
<table id="posix-vs-gio">
|
|
<title>Comparison of POSIX and GIO concepts</title>
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>POSIX</entry><entry>GIO</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row><entry>char *path</entry><entry>GFile *file</entry></row>
|
|
<row><entry>struct stat *buf</entry><entry>GFileInfo *info</entry></row>
|
|
<row><entry>struct statvfs *buf</entry><entry>GFileInfo *info</entry></row>
|
|
<row><entry morerows="1">int fd</entry><entry>GInputStream *in</entry></row>
|
|
<row><entry>GOutputStream *out</entry></row>
|
|
<row><entry>DIR *</entry><entry>GFileEnumerator *enum</entry></row>
|
|
<row><entry>fstab entry</entry><entry>GUnixMountPoint *mount_point</entry></row>
|
|
<row><entry>mtab entry</entry><entry>GUnixMountEntry *mount_entry</entry></row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
</chapter>
|
|
|
|
<chapter>
|
|
<title>Migrating from GnomeVFS to GIO</title>
|
|
|
|
<table id="gnome-vfs-vs-gio">
|
|
<title>Comparison of GnomeVFS and GIO concepts</title>
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>GnomeVFS</entry><entry>GIO</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row><entry>GnomeVFSURI</entry><entry>GFile</entry></row>
|
|
<row><entry>GnomeVFSFileInfo</entry><entry>GFileInfo</entry></row>
|
|
<row><entry>GnomeVFSResult</entry><entry>GError, with G_IO_ERROR values</entry></row>
|
|
<row><entry>GnomeVFSHandle & GnomeVFSAsyncHandle</entry><entry>GInputStream or GOutputStream</entry></row>
|
|
<row><entry>GnomeVFSDirectoryHandle</entry><entry>GFileEnumerator</entry></row>
|
|
<row><entry>mime type</entry><entry>content type</entry></row>
|
|
<row><entry>GnomeVFSMonitor</entry><entry>GFileMonitor</entry></row>
|
|
<row><entry>GnomeVFSVolumeMonitor</entry><entry>GVolumeMonitor</entry></row>
|
|
<row><entry>GnomeVFSVolume</entry><entry>GMount</entry></row>
|
|
<row><entry>GnomeVFSDrive</entry><entry>GVolume</entry></row>
|
|
<row><entry>-</entry><entry>GDrive</entry></row>
|
|
<row><entry>GnomeVFSContext</entry><entry>GCancellable</entry></row>
|
|
<row><entry>gnome_vfs_async_cancel</entry><entry>g_cancellable_cancel</entry></row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<section>
|
|
<title>Trash handling</title>
|
|
|
|
<para>
|
|
The handling of trashed files has been changed in GIO, compared
|
|
to gnome-vfs. gnome-vfs has a home-grown trash implementation that
|
|
predates the freedesktop.org <ulink url="http://www.freedesktop.org/wiki/Specifications/trash-spec">Desktop Trash Can</ulink> specification
|
|
that is implemented in GIO. The location for storing trashed files
|
|
has changed from <filename>$HOME/.Trash</filename> to
|
|
<filename>$HOME/.local/share/Trash</filename> (or more correctly
|
|
<filename>$XDG_DATA_HOME/Trash</filename>), which means that
|
|
there is a need for migrating files that have been trashed by
|
|
gnome-vfs to the new location.
|
|
</para>
|
|
<para>
|
|
In gnome-vfs, the <filename>trash://</filename> scheme offering a
|
|
merged view of all trash directories was implemented in nautilus,
|
|
and trash-handling applications had to find and monitor all trash
|
|
directories themselves. With GIO, the <filename>trash://</filename>
|
|
implementation has been moved to gvfs and applications can simply
|
|
monitor that location:
|
|
</para>
|
|
<informalexample><programlisting>
|
|
static void
|
|
file_changed (GFileMonitor *file_monitor,
|
|
GFile *child,
|
|
GFile *other_file,
|
|
GFileMonitorEvent event_type,
|
|
gpointer user_data)
|
|
{
|
|
switch (event_type)
|
|
{
|
|
case G_FILE_MONITOR_EVENT_DELETED:
|
|
g_print ("'%s' removed from trash\n", g_file_get_basename (child));
|
|
break;
|
|
case G_FILE_MONITOR_EVENT_CREATED:
|
|
g_print ("'%s' added to trash\n", g_file_get_basename (child));
|
|
break;
|
|
default: ;
|
|
}
|
|
}
|
|
|
|
static void
|
|
start_monitoring_trash (void)
|
|
{
|
|
GFile *file;
|
|
GFileMonitor *monitor;
|
|
|
|
file = g_file_new_for_uri ("trash://");
|
|
monitor = g_file_monitor_directory (file, 0, NULL, NULL);
|
|
g_object_unref (file);
|
|
|
|
g_signal_connect (monitor, "changed", G_CALLBACK (file_changed), NULL);
|
|
|
|
/* ... */
|
|
|
|
}
|
|
</programlisting></informalexample>
|
|
<para>
|
|
GIO exposes some useful metadata about trashed files. There are
|
|
trash::orig-path and trash::deletion-date attributes. The
|
|
standard::icon attribute of the <filename>trash://</filename>
|
|
itself provides a suitable icon for displaying the trash can on
|
|
the desktop. If you are using this icon, make sure to monitor
|
|
this attribute for changes, since the icon may be updated to
|
|
reflect that state of the trash can.
|
|
</para>
|
|
<para>
|
|
Moving a file to the trash is much simpler with GIO. Instead of
|
|
using gnome_vfs_find_directory() with %GNOME_VFS_DIRECTORY_KIND_TRASH
|
|
to find out where to move the trashed file, just use the g_file_trash()
|
|
function.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Operations on multiple files</title>
|
|
|
|
<para>
|
|
gnome-vfs has the dreaded gnome_vfs_xfer_uri_list() function which
|
|
has tons of options and offers the equivalent of cp, mv, ln, mkdir
|
|
and rm at the same time.
|
|
</para>
|
|
<para>
|
|
GIO offers a much simpler I/O scheduler functionality instead, that
|
|
lets you schedule a function to be called in a separate thread, or
|
|
if threads are not available, as an idle in the mainloop.
|
|
See g_io_scheduler_push_job().
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section>
|
|
<title>Mime monitoring</title>
|
|
|
|
<para>
|
|
gnome-vfs offered a way to monitor the association between mime types
|
|
and default handlers for changes, with the #GnomeVFSMIMEMonitor object.
|
|
GIO does not offer a replacement for this functionality at this time,
|
|
since we have not found a compelling use case where
|
|
#GnomeVFSMIMEMonitor was used. If you think you have such a use
|
|
case, please report it at
|
|
<ulink url="http://bugzilla.gnome.org">bugzilla.gnome.org</ulink>.
|
|
</para>
|
|
</section>
|
|
</chapter>
|
|
|
|
<chapter>
|
|
<title>Migrating from GConf to GSettings</title>
|
|
|
|
<section>
|
|
<title>Before you start</title>
|
|
|
|
<para>
|
|
Converting individual applications and their settings from GConf to
|
|
GSettings can be done at will. But desktop-wide settings like font or
|
|
theme settings often have consumers in multiple modules. Therefore,
|
|
some consideration has to go into making sure that all users of a setting
|
|
are converted to GSettings at the same time or that the program
|
|
responsible for configuring that setting continues to update the value in
|
|
both places.
|
|
</para>
|
|
<para>
|
|
It is always a good idea to have a look at how others have handled
|
|
similar problems before. An examplaric conversion can be found e.g.
|
|
in the <ulink url="http://git.gnome.org/browse/gnome-utils/log/?h=gsettings-tutorial">gsettings-tutorial</ulink> branch of gnome-utils.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Conceptual differences</title>
|
|
|
|
<para>
|
|
Conceptually, GConf and GSettings are fairly similar. Both
|
|
have a concept of pluggable backends. Both keep information
|
|
about keys and their types in schemas. Both have a concept of
|
|
mandatory values, which lets you implement lock-down.
|
|
</para>
|
|
<para>
|
|
There are some differences in the approach to schemas. GConf
|
|
installs the schemas into the database and has API to handle
|
|
schema information (gconf_client_get_default_from_schema(),
|
|
gconf_value_get_schema(), etc). GSettings on the other hand
|
|
assumes that an application knows its own schemas, and does
|
|
not provide API to handle schema information at runtime.
|
|
GSettings is also more strict about requiring a schema whenever
|
|
you want to read or write a key. To deal with more free-form
|
|
information that would appear in schema-less entries in GConf,
|
|
GSettings allows for schemas to be 'relocatable'.
|
|
</para>
|
|
<para>
|
|
One difference in the way applications interact with their
|
|
settings is that with GConf you interact with a tree of
|
|
settings (ie the keys you pass to functions when reading
|
|
or writing values are actually paths with the actual name
|
|
of the key as the last element. With GSettings, you create
|
|
a GSettings object which has an implicit prefix that determines
|
|
where the settings get stored in the global tree of settings,
|
|
but the keys you pass when reading or writing values are just
|
|
the key names, not the full path.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>GConfClient API conversion</title>
|
|
|
|
<para>
|
|
Most people use GConf via the high-level #GConfClient API.
|
|
The corresponding API is the #GSettings object. While not
|
|
every GConfClient function has a direct GSettings equivalent,
|
|
many do:
|
|
<table id="gconf-client-vs-gsettings">
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>GConfClient</entry><entry>GSettings</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row><entry>gconf_client_set()</entry><entry>g_settings_set()</entry></row>
|
|
<row><entry>gconf_client_get()</entry><entry>g_settings_get()</entry></row>
|
|
<row><entry>gconf_client_get_bool()</entry><entry>g_settings_get_boolean()</entry></row>
|
|
<row><entry>gconf_client_set_bool()</entry><entry>g_settings_set_boolean()</entry></row>
|
|
<row><entry>gconf_client_get_int()</entry><entry>g_settings_get_int()</entry></row>
|
|
<row><entry>gconf_client_set_int()</entry><entry>g_settings_set_int()</entry></row>
|
|
<row><entry>gconf_client_get_float()</entry><entry>g_settings_get_double()</entry></row>
|
|
<row><entry>gconf_client_set_float()</entry><entry>g_settings_set_double()</entry></row>
|
|
<row><entry>gconf_client_get_string()</entry><entry>g_settings_get_string()</entry></row>
|
|
<row><entry>gconf_client_set_string()</entry><entry>g_settings_set_string()</entry></row>
|
|
<row><entry>gconf_client_get_list()</entry><entry>for string lists, see g_settings_get_strv(), else see g_settings_get_value() and #GVariant API</entry></row>
|
|
<row><entry>gconf_client_set_list()</entry><entry>for string lists, see g_settings_set_strv(), else see g_settings_set_value() and #GVariant API</entry></row>
|
|
<row><entry>gconf_entry_get_is_writable()</entry><entry>g_settings_is_writable()</entry></row>
|
|
<row><entry>gconf_client_notify_add()</entry><entry>not required, the #GSettings::changed signal is emitted automatically</entry></row>
|
|
<row><entry>gconf_client_add_dir()</entry><entry>not required, each GSettings instance automatically watches all keys in its path</entry></row>
|
|
<row><entry>#GConfChangeSet</entry><entry>g_settings_delay(), g_settings_apply()</entry></row>
|
|
<row><entry>gconf_client_get_default_from_schema()</entry><entry>no equivalent, applications are expected to know their schema</entry></row>
|
|
<row><entry>gconf_client_all_entries()</entry><entry>no equivalent, applications are expected to know their schema, and GSettings does not allow schema-less entries</entry></row>
|
|
<row><entry>gconf_client_get_without_default()</entry><entry>no equivalent</entry></row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
<para>
|
|
There is a pattern that is sometimes used for GConf, where a setting can have
|
|
explicit 'value A', explicit 'value B' or 'use the system default'. With GConf,
|
|
'use the system default' is sometimes implemented by unsetting the user value.
|
|
</para>
|
|
<para>
|
|
This is not possible in GSettings, since it does not have API to determine if a value
|
|
is the default and does not let you unset values. The recommended way (and much
|
|
clearer) way in which this can be implemented in GSettings is to have a separate
|
|
'use-system-default' boolean setting.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Change notification</title>
|
|
|
|
<para>
|
|
GConf requires you to call gconf_client_add_dir() and
|
|
gconf_client_notify_add() to get change notification. With
|
|
GSettings, this is not necessary; signals get emitted automatically
|
|
for every change.
|
|
</para>
|
|
<para>
|
|
The #GSettings::changed signal is emitted for each changed key.
|
|
There is also a #GSettings::change-event signal that you can handle
|
|
if you need to see groups of keys that get changed at the same time.
|
|
</para>
|
|
<para>
|
|
GSettings also notifies you about changes in writability of keys,
|
|
with the #GSettings::writable-changed signal (and the
|
|
#GSettings::writable-change-event signal).
|
|
</para>
|
|
</section>
|
|
|
|
<section><title>Change sets</title>
|
|
<para>
|
|
GConf has a a concept of a set of changes which can be applied or reverted
|
|
at once: #GConfChangeSet (GConf doesn't actually apply changes atomically,
|
|
which is one of its shortcomings).
|
|
</para>
|
|
<para>
|
|
Instead of a separate object to represent a change set, GSettings has a
|
|
'delayed-apply' mode, which can be turned on for a GSettings object by
|
|
calling g_settings_delay(). In this mode, changes done to the GSettings
|
|
object are not applied - they are still visible when calling g_settings_get()
|
|
<emphasis>on the same object</emphasis>, but not to other GSettings instances
|
|
or even other processes.
|
|
</para>
|
|
<para>
|
|
To apply the pending changes all at once (GSettings <emphasis>does</emphasis>
|
|
atomicity here), call g_settings_apply(). To revert the pending changes,
|
|
call g_settings_revert() or just drop the reference to the #GSettings object.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Schema conversion</title>
|
|
|
|
<para>
|
|
One possible pitfall in doing schema conversion is that the default
|
|
values in GSettings schemas are parsed by the #GVariant parser.
|
|
This means that strings need to include quotes in the XML. Also note
|
|
that the types are now specified as #GVariant type strings.
|
|
<programlisting>
|
|
<![CDATA[
|
|
<type>string</type>
|
|
<default>rgb</default>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key name="rgba-order" type="s">
|
|
<default>'rgb'</default> <!-- note quotes -->
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Another possible complication is that GConf specifies full paths
|
|
for each key, while a GSettings schema has a 'path' attribute that
|
|
contains the prefix for all the keys in the schema, and individual
|
|
keys just have a simple name. So
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key>/schemas/desktop/gnome/font_rendering/antialiasing</key>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<schema id="org.gnome.font" path="/desktop/gnome/font_rendering/">
|
|
<key name="antialiasing" type="s">
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Default values can be localized in both GConf and GSettings schemas,
|
|
but GSettings uses gettext for the localization, so
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key>/schemas/apps/my_app/font_size</key>
|
|
<locale name="C">
|
|
<default>18</default>
|
|
</locale>
|
|
<locale name="be">
|
|
<default>24</default>
|
|
</locale>
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key name="font-size" type="i">
|
|
<default l10n="messages" context="font_size">18</default>
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
Note how we used the context attribute to add msgctxt - "18" is not a
|
|
good string to look up in gettext by itself. Also note that the value
|
|
24 is not present in the schema anymore. It has to be added to the gettext
|
|
catalog for "be" instead.
|
|
</para>
|
|
<para>
|
|
GSettings schemas have more stringent restrictions on key names
|
|
than GConf. Key names in GSettings are restricted to at most 32
|
|
characters, and must only consist of lowercase characters, numbers
|
|
and dashes, with no consecutive dashes. The first character must
|
|
not be a number or dash, and the last character cannot be '-'.
|
|
The <link linkend="gschema-compile">gschema-compile</link> schema
|
|
compiler has a <option>--allow-any-name</option> that lets you
|
|
ignore these restrictions. Note that this option is only meant
|
|
to ease the process of porting your application, allowing parts
|
|
of your application to continue to access GConf and parts to use
|
|
GSettings. By the time you have finished porting your application
|
|
you must ensure that all key names are valid.
|
|
</para>
|
|
<para>
|
|
GIO comes with a commandline tool
|
|
<link linkend="gsettings-schema-convert">gsettings-schema-convert</link>
|
|
that can help with the task of converting a GConf schema into
|
|
an equivalent GSettings schema. The tool is not perfect and
|
|
may need assistence in some cases.
|
|
</para>
|
|
</section>
|
|
|
|
<section><title>Data conversion</title>
|
|
<para>
|
|
GConf comes with a utility called <command>gsettings-data-convert</command>,
|
|
which is designed to help with the task of migrating user settings from
|
|
GConf into GSetting. <command>gsettings-data-convert</command> can be run
|
|
manually, but it is designed to be run automatically, every time a user
|
|
logs in. It keeps track of the conversion that it has already done, and it
|
|
is harmless to run it more than once.
|
|
</para>
|
|
<para>
|
|
To make use of this utility, you must install a keyfile in the
|
|
<filename>/usr/share/gsettings-data-convert</filename> which lists the GSettings
|
|
and GConf paths to map to each other, for each schema that you want to migrate
|
|
user data for.
|
|
</para>
|
|
<para>
|
|
Here is an example:
|
|
<programlisting>
|
|
<![CDATA[
|
|
[org.gnome.fonts]
|
|
antialiasing = /desktop/gnome/font_rendering/antialiasing
|
|
dpi = /desktop/gnome/font_rendering/dpi
|
|
hinting = /desktop/gnome/font_rendering/hinting
|
|
rgba-order = /desktop/gnome/font_rendering/rgba_order
|
|
|
|
[apps.myapp]
|
|
some-odd-key1 = /apps/myapp/some_ODD-key1
|
|
]]>
|
|
</programlisting>
|
|
The last key demonstrates that it may be necessary to modify the key name
|
|
to comply with stricter GSettings key name rules. Of course, that means your
|
|
application must make the corresponding adjustments.
|
|
</para>
|
|
<para>
|
|
There are some limitations: <command>gsettings-data-convert</command> does not
|
|
do any transformation of the values. And it does not handle complex GConf types
|
|
other than lists of strings or integers.
|
|
</para>
|
|
</section>
|
|
</chapter>
|
|
|
|
</part>
|