path: root/doc/gconf/tmpl/gconf-backend.sgml

<!-- ##### SECTION Title ##### -->
gconf-backend

<!-- ##### SECTION Short_Description ##### -->


<!-- ##### SECTION Long_Description ##### -->
<para>

</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### SECTION Image ##### -->


<!-- ##### STRUCT GConfBackendVTable ##### -->
<para>
The #GConfBackendVTable is a table of methods that any GConf backend must
implement.  The dynamically loaded library module should export a function
called gconf_backend_get_vtable() that returns a pointer to a
#GConfBackendVTable.
</para>

<para>
Here is the specification of the vtable members:

<informaltable pgwide="1" frame="none">
<tgroup cols="2"><colspec colwidth="2*"/><colspec colwidth="8*"/>
<tbody>

<row>
<entry>@vtable_size</entry> 
<entry>
The size of the vtable structure. This is used by the daemon to ensure that
a mismatch between the version of GConf the backend was compiled against and
the version the daemon was compiled against can be handled gracefully. Set
this field to sizeof (GConfBackendVtable).
</entry>
</row>
 
<row>
<entry>@shutdown</entry> 
<entry>Called prior to unloading the dynamic
module. Should ensure that no functions or static/global variables from the
module will ever be accessed again. Should free any memory that the backend
no longer needs.
</entry>
</row>
 
<row>
<entry>@resolve_address</entry> 

<entry>
Should create a #GConfSource for accessing the supplied address. Should set the
%GCONF_SOURCE_ALL_READABLE and %GCONF_SOURCE_ALL_WRITEABLE flags if
appropriate. If these are not set, the backend must implement the @writable and
@readable methods. If <symbol>NULL</symbol> is returned, then the error should
be set.
</entry>

</row>
 
<row>
<entry>@lock</entry> 

<entry>If the backend is thread safe (does its own locking or whatever), then
@lock and @unlock can be <symbol>NULL</symbol>.  If the backend requires a lock
for each source, then @lock and @unlock should lock/unlock that lock. If the
backend has a global lock for all uses of the backend, then @lock and @unlock
should ignore their arguments and lock the entire backend.
</entry>

</row>
 

<row>
<entry>@unlock</entry>
<entry>See description of @lock.</entry>
</row>
 

<row>
<entry>@readable</entry> 

<entry>
If the %GCONF_SOURCE_ALL_READABLE flag is set, this method is never called and
may be <symbol>NULL</symbol>. If %GCONF_SOURCE_ALL_READABLE is unset, and this
method is <symbol>NULL</symbol>, then the source is write-only. If this method
is implemented, it should return <symbol>TRUE</symbol> if the given key could be
read from the given source. <symbol>TRUE</symbol> should be returned even if the
key is unset; this function returns something similar to permissions, it is not
asking whether the key exists. <emphasis>If an error is set, then
<symbol>FALSE</symbol> must be returned.</emphasis>
</entry>

</row>
 

<row>
<entry>@writable</entry>
<entry>Analagous to @readable, but for writing.</entry>
</row>
 

<row>
<entry>@query_value</entry>

<entry>This method must be implemented if the source is readable. It returns the
value of a key.  The "locales" argument is a <symbol>NULL</symbol>-terminated
vector of locale names, where the first locale in the vector is the preferred
locale, the next is the second choice, etc. if the "schema_name" argument is
non-<symbol>NULL</symbol>, then it should be filled with an allocated string
giving the name of the schema attached to the key, if and only if
<symbol>NULL</symbol> is returned. This is an optimization to avoid looking up
the same key again in the database if it's unset and we need to ask for its
default value from the schema. If <symbol>NULL</symbol> is returned, indicating
that the key is unset, then schema_name should not be filled in. If this method
sets an error, <symbol>NULL</symbol> must be returned. It may not set an error
while also returning a value. The returned value will be destroyed by the
caller, so should be a copy of the backend's internal data.
</entry>
</row>

<row>
<entry>@query_metainfo</entry>

<entry>This method must be implemented. If any metainfo is
available about a key, it returns a #GConfMetaInfo with that metainfo set.  If
none is available, <symbol>NULL</symbol> is returned. <symbol>NULL</symbol>
should also be returned if an error is set.
</entry>

</row>
 

<row>
<entry>@set_value</entry>

<entry>This method must be implemented if the source is
writable. It sets the value of a key. If the key is already set, its value
should be replaced. Setting a value should update the modification time of the
key.
</entry>

</row>
 

<row>
<entry>@all_entries</entry>

<entry>This method must be implemented. It returns a list of all keys in the
given directory for which some information is available (metainfo or
values). The returned list should contain #GConfEntry objects. On error,
<symbol>NULL</symbol> should be returned and the error set. Subdirectories
should not be included in the returned list. The list and the #GConfEntry
objects will be freed by the caller.
</entry>

</row>
 

<row>
<entry>@all_subdirs</entry>

<entry>This method must be implemented. It returns a list of all the subdirectories in a given
directory.  It should return the subdirectories as relative paths, i.e. there
should not be any slashes in the subdirectory name. Each subdirectory in the list
should be an allocated string; the list and the strings will be freed by the caller.
</entry>

</row>
 

<row>
<entry>@unset_value</entry>

<entry>If the given key has a value, then this method should unset the value.
If a value is unset, subsequent calls to @query_value should return
<symbol>NULL</symbol>. If the locale string passed in to @unset_value is
non-<symbol>NULL</symbol>, then only the value for that locale should be
unset. If <symbol>NULL</symbol>, the value should be globally unset for all
locales.
</entry>

</row>
 

<row>
<entry>@dir_exists</entry>

<entry>
Determines whether a directory exists. Should return
<symbol>TRUE</symbol> if there is a directory with the given name.
</entry>

</row>
 

<row>
<entry>@remove_dir</entry>

<entry>
Should remove a directory, recursively: including all its subdirectories and 
all the values and keys inside the directory.
</entry>

</row>
 

<row>
<entry>@set_schema</entry>

<entry>Should associate a schema name with a key.
</entry>

</row>
 

<row>
<entry>@sync_all</entry>

<entry>
Should ensure that all data is stored on permanent media, or whatever makes
sense for the backend. Called periodically by the GConf daemon.
</entry>

</row>
 

<row>
<entry>@destroy_source</entry>

<entry>
Should destroy a source obtained with @resolve_address.
</entry>

</row>
 
<row>
<entry>@clear_cache</entry>

<entry>
Discard any cached data after saving the data to permanent storage.
</entry>

</row>
 
<row>
<entry>@blow_away_locks</entry>

<entry>
Unconditionally discard any locks whether they are stale or otherwise in
order to force the backend to be able to obtain access to its data store.
</entry>

</row>
 
<row>
<entry>@set_notify_func</entry>

<entry>
If the backend wishes to notify the daemon of changes in the value of
keys it must implement this method. In order to notify the daemon
of a change, the backend should invoke the supplied @notify_func with
@user_data. Backends must not notify the daemon of changes which the
daemon has not expressed interest in by adding a listener with
@add_listener. Also, the backend must make every effort to minimise the
number of notifications it emits. For example, if the daemon has added
a listener for /apps and another for /apps/foo and the value of
/apps/foo/bar changes, the backend should only emit a single notification.
</entry>

</row>
 
<row>
<entry>@add_listener</entry>

<entry>
If it is possible for entries to be changed concurrently by another
daemon, the backend may support notifying the daemon (and any listening
clients) of such changes. This function should add a listener to a
section of the tree and when any of the following events occur, the
backend should invoke the notify function with the key that has changed:
 <itemizedlist mark="bullet">
  <listitem>
    <para>If the entry is set or unset</para>
  </listitem>
  <listitem>
    <para>If the entry's value changes</para>
  </listitem>
  <listitem>
    <para>If the entry's schema name changes</para>
  </listitem>
  <listitem>
    <para>
      If the entry is a schema and its value in <emphasis>any</emphasis>
      locale changes
    </para>
  </listitem>
 </itemizedlist>
Note, the backend should <emphasis>not</emphasis> notify the daemon of
any changes that originated from the daemon itself.
</entry>

</row>

<row>
<entry>@remove_listener</entry>

<entry>
Remove a listener added with @add_listener. The listener is identified
by the integer supplied.
</entry>

</row>
 
</tbody></tgroup></informaltable>
</para>

@vtable_size: 
@shutdown: 
@resolve_address: 
@lock: 
@unlock: 
@readable: 
@writable: 
@query_value: 
@query_metainfo: 
@set_value: 
@all_entries: 
@all_subdirs: 
@unset_value: 
@dir_exists: 
@remove_dir: 
@set_schema: 
@sync_all: 
@destroy_source: 
@clear_cache: 
@blow_away_locks: 
@set_notify_func: 
@add_listener: 
@remove_listener: 

<!-- ##### STRUCT GConfBackend ##### -->
<para>

</para>

@name: 
@refcount: 
@vtable: 
@module: 

<!-- ##### FUNCTION gconf_address_backend ##### -->
<para>

</para>

@address: 
@Returns: 


<!-- ##### FUNCTION gconf_address_resource ##### -->
<para>

</para>

@address: 
@Returns: 


<!-- ##### FUNCTION gconf_backend_file ##### -->
<para>

</para>

@address: 
@Returns: 


<!-- ##### FUNCTION gconf_get_backend ##### -->
<para>

</para>

@address: 
@err: 
@Returns: 


<!-- ##### FUNCTION gconf_backend_ref ##### -->
<para>

</para>

@backend: 


<!-- ##### FUNCTION gconf_backend_unref ##### -->
<para>

</para>

@backend: 


<!-- ##### FUNCTION gconf_backend_resolve_address ##### -->
<para>

</para>

@backend: 
@address: 
@err: 
@Returns: