Document the permission store API

Add doc comments to the xml.

data/org.freedesktop.impl.portal.PermissionStore.xml

@@ -24,8 +24,35 @@
 -->
 
 <node name="/" xmlns:doc="http://www.freedesktop.org/dbus/1.0/doc.dtd">
+  <!--
+      org.freedesktop.impl.portal.PermissionStore:
+      @short_description: Database to store permissions
+
+      The permission store can be used by portals to store permissions
+      that sandboxed applications have to various resources, such as
+      files outside the sandbox.
+
+      Since the resources managed by portals can be varied, the permission
+      store is fairly free-form: there can be multiple tables; resources are
+      identified by an ID, as are applications, and permissions are stored as
+      string arrays. None of these strings are interpreted by the permission
+      store in any way.
+
+      In addition, the permission store allows to associate extra data
+      (in the form of a GVariant) with each resource.
+  -->
   <interface name='org.freedesktop.impl.portal.PermissionStore'>
 
+    <!--
+        Lookup:
+        @table: the name of the table to use
+        @id: the resource ID to look up
+        @permissions: map from application ID to permissions
+        @data: data that is associated with the resource
+
+        Looks up the entry for a resource in one of the tables and returns
+        all associated application permissions and data.
+    -->
     <method name="Lookup">
       <arg name='table' type='s' direction='in'/>
       <arg name='id' type='s' direction='in'/>
@@ -33,6 +60,16 @@
       <arg name='data' type='v' direction='out'/>
     </method>
 
+    <!--
+        Set:
+        @table: the name of the table to use
+        @create: whether to create the table if it does not exist
+        @id: the resource ID to modify
+        @app_permissions: map from application ID to permissions
+        @data: data to associate with the resource
+
+        Writes the entry for a resource in the given table.
+    -->
     <method name="Set">
       <arg name='table' type='s' direction='in'/>
       <arg name='create' type='b' direction='in'/>
@@ -41,11 +78,27 @@
       <arg name='data' type='v' direction='in'/>
     </method>
 
+    <!--
+        Delete:
+        @table: the name of the table to use
+        @id: the resource ID to delete
+
+        Removes the entry for a resource in the given table.
+    -->
     <method name="Delete">
       <arg name='table' type='s' direction='in'/>
       <arg name='id' type='s' direction='in'/>
     </method>
 
+    <!--
+        SetValue:
+        @table: the name of the table to use
+        @create: whether to create the table if it does not exist
+        @id: the resource ID to modify
+        @data: data to associate with the resource
+
+        Sets just the data for a resource in the given table.
+    -->
     <method name="SetValue">
       <arg name='table' type='s' direction='in'/>
       <arg name='create' type='b' direction='in'/>
@@ -53,6 +106,17 @@
       <arg name='data' type='v' direction='in'/>
     </method>
 
+    <!--
+        SetPermission:
+        @table: the name of the table to use
+        @create: whether to create the table if it does not exist
+        @id: the resource ID to modify
+        @app: the application ID to modify
+        @permissions: permissions to set
+
+        Sets the permissions for an application and a resource
+        in the given table.
+    -->
     <method name="SetPermission">
       <arg name='table' type='s' direction='in'/>
       <arg name='create' type='b' direction='in'/>
@@ -61,11 +125,31 @@
       <arg name='permissions' type='as' direction='in'/>
     </method>
 
+    <!--
+        List:
+        @table: the name of the table to use
+        @ids: IDs of all resources that are present in the table
+
+        Returns all the resources that are present in the table.
+    -->
     <method name="List">
       <arg name='table' type='s' direction='in'/>
       <arg name='ids' type='as' direction='out'/>
     </method>
 
+    <!--
+        Changed:
+        @table: the name of the table
+        @ids: IDs of the changed resource
+        @deleted: whether the resource was deleted
+        @data: the data that is associated the resource
+        @permissions: the permissions that are associated with the resource
+
+        The Changed signal is emitted when the entry for a resource
+        is modified or deleted. If the entry was deleted, then @data
+        and @permissions contain the last values that were found in the
+        database. If the entry was modified, they contain the new values.
+    -->
     <signal name="Changed">
       <arg name='table' type='s' direction='out'/>
       <arg name='id' type='s' direction='out'/>