[rygel] server: Query SystemUpdateID from backend

[Jens Georg <jensgeorg src gnome org>]

commit b3d9c78ef5781744a7e938427523204d3191ab9b
Author: Jens Georg <jensg openismus com>
Date:   Tue Dec 11 20:39:03 2012 +0100

    server: Query SystemUpdateID from backend

 src/librygel-server/rygel-content-directory.vala   |    2 ++
 src/librygel-server/rygel-trackable-container.vala |    9 +++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)
---
diff --git a/src/librygel-server/rygel-content-directory.vala b/src/librygel-server/rygel-content-directory.vala
index 1cc952c..3834b6b 100644
--- a/src/librygel-server/rygel-content-directory.vala
+++ b/src/librygel-server/rygel-content-directory.vala
@@ -119,8 +119,10 @@ internal class Rygel.ContentDirectory: Service {
         if (this.root_container is TrackableContainer) {
             var trackable = this.root_container as TrackableContainer;
             this.service_reset_token = trackable.get_service_reset_token ();
+            this.system_update_id = trackable.get_system_update_id ();
         } else {
             this.service_reset_token = UUID.get ();
+            this.system_update_id = 0;
         }
 
         this.action_invoked["Browse"].connect (this.browse_cb);
diff --git a/src/librygel-server/rygel-trackable-container.vala b/src/librygel-server/rygel-trackable-container.vala
index dbd6371..431928d 100644
--- a/src/librygel-server/rygel-trackable-container.vala
+++ b/src/librygel-server/rygel-trackable-container.vala
@@ -86,6 +86,15 @@ public interface Rygel.TrackableContainer : Rygel.MediaContainer {
      */
     public virtual void set_service_reset_token (string token) {}
 
+    /**
+     * Query the current system update id.
+     * This should be overriden by the root container of the back-end
+     * implementation.
+     *
+     * @return: the current SystemUpdateID as persisted by the back-end.
+     */
+    public virtual uint32 get_system_update_id () { return 0; }
+
     private void thaw_events () {
         // Forward events.
     }