diff --git a/include/private/surfaceflinger/SharedBufferStack.h b/include/private/surfaceflinger/SharedBufferStack.h
index d689667..d6ae5e9 100644
--- a/include/private/surfaceflinger/SharedBufferStack.h
+++ b/include/private/surfaceflinger/SharedBufferStack.h
@@ -114,8 +114,9 @@
 
     int32_t     identity;       // surface's identity (const)
     int32_t     token;          // surface's token (for debugging)
-    int32_t     reserved32[1];
     Statistics  stats;
+    int8_t      headBuf;        // last retired buffer
+    uint8_t     reservedBytes[3];
     int32_t     reserved;
     BufferData  buffers[NUM_BUFFER_MAX];     // 1024 bytes
 };
@@ -201,6 +202,7 @@
     status_t undoDequeue(int buf);
     
     status_t lock(int buf);
+    status_t cancel(int buf);
     status_t queue(int buf);
     bool needNewBuffer(int buffer) const;
     status_t setDirtyRegion(int buffer, const Region& reg);
@@ -230,8 +232,9 @@
         inline ssize_t operator()();
     };
 
-    struct UndoDequeueUpdate : public UpdateBase {
-        inline UndoDequeueUpdate(SharedBufferBase* sbb);
+    struct CancelUpdate : public UpdateBase {
+        int tail, buf;
+        inline CancelUpdate(SharedBufferBase* sbb, int tail, int buf);
         inline ssize_t operator()();
     };
 
@@ -256,7 +259,6 @@
     int mNumBuffers;
 
     int32_t tail;
-    int32_t undoDequeueTail;
     int32_t queued_head;
     // statistics...
     nsecs_t mDequeueTime[SharedBufferStack::NUM_BUFFER_MAX];
diff --git a/include/surfaceflinger/Surface.h b/include/surfaceflinger/Surface.h
index 7c5a39b..22684db 100644
--- a/include/surfaceflinger/Surface.h
+++ b/include/surfaceflinger/Surface.h
@@ -199,6 +199,7 @@
      */
     static int setSwapInterval(ANativeWindow* window, int interval);
     static int dequeueBuffer(ANativeWindow* window, android_native_buffer_t** buffer);
+    static int cancelBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int lockBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int queueBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int query(ANativeWindow* window, int what, int* value);
@@ -207,6 +208,7 @@
     int dequeueBuffer(android_native_buffer_t** buffer);
     int lockBuffer(android_native_buffer_t* buffer);
     int queueBuffer(android_native_buffer_t* buffer);
+    int cancelBuffer(android_native_buffer_t* buffer);
     int query(int what, int* value);
     int perform(int operation, va_list args);
 
diff --git a/include/ui/egl/android_natives.h b/include/ui/egl/android_natives.h
index d59d72b..654d0f3 100644
--- a/include/ui/egl/android_natives.h
+++ b/include/ui/egl/android_natives.h
@@ -218,7 +218,17 @@
     int     (*perform)(struct ANativeWindow* window,
                 int operation, ... );
     
-    void* reserved_proc[3];
+    /*
+     * hook used to cancel a buffer that has been dequeued.
+     * No synchronization is performed between dequeue() and cancel(), so
+     * either external synchronization is needed, or these functions must be
+     * called from the same thread.
+     */
+    int     (*cancelBuffer)(struct ANativeWindow* window,
+                struct android_native_buffer_t* buffer);
+
+
+    void* reserved_proc[2];
 };
 
 // Backwards compatibility...  please switch to ANativeWindow.