traffic-control: (fixes #2389) Internal queues need to notify their queue disc of packet drops

src/network/utils/queue.cc

@@ -97,19 +97,18 @@ bool
 Queue::Enqueue (Ptr<QueueItem> item)
 {
   NS_LOG_FUNCTION (this << item);
-  Ptr<Packet> p = item->GetPacket ();
 
   if (m_mode == QUEUE_MODE_PACKETS && (m_nPackets.Get () >= m_maxPackets))
     {
       NS_LOG_LOGIC ("Queue full (at max packets) -- dropping pkt");
-      Drop (p);
+      Drop (item);
       return false;
     }
 
   if (m_mode == QUEUE_MODE_BYTES && (m_nBytes.Get () + item->GetPacketSize () > m_maxBytes))
     {
       NS_LOG_LOGIC ("Queue full (packet would exceed max bytes) -- dropping pkt");
-      Drop (p);
+      Drop (item);
       return false;
     }
 
@@ -319,15 +318,33 @@ Queue::GetMaxBytes (void) const
 }
 
 void
-Queue::Drop (Ptr<Packet> p)
+Queue::SetDropCallback (DropCallback cb)
 {
-  NS_LOG_FUNCTION (this << p);
+  m_dropCallback = cb;
+}
+
+void
+Queue::NotifyDrop (Ptr<QueueItem> item)
+{
+  NS_LOG_FUNCTION (this << item);
+
+  if (!m_dropCallback.IsNull ())
+    {
+      m_dropCallback (item);
+    }
+}
+
+void
+Queue::Drop (Ptr<QueueItem> item)
+{
+  NS_LOG_FUNCTION (this << item);
 
   m_nTotalDroppedPackets++;
-  m_nTotalDroppedBytes += p->GetSize ();
+  m_nTotalDroppedBytes += item->GetPacketSize ();
 
   NS_LOG_LOGIC ("m_traceDrop (p)");
-  m_traceDrop (p);
+  m_traceDrop (item->GetPacket ());
+  NotifyDrop (item);
 }
 
 } // namespace ns3

src/network/utils/queue.h

@@ -190,16 +190,28 @@ public:
   double GetDroppedPacketsPerSecondVariance (void);
 #endif
 
+  /// Callback set by the object (e.g., a queue disc) that wants to be notified of a packet drop
+  typedef Callback<void, Ptr<QueueItem> > DropCallback;
+
+  /**
+   * \brief Set the drop callback
+   * \param cb the callback to set
+   *
+   * Called when a queue is added to a queue disc in order to set a
+   * callback to the Drop method of the queue disc.
+   */
+  virtual void SetDropCallback (DropCallback cb);
+
 protected:
   /**
    * \brief Drop a packet
-   * \param p packet that was dropped
+   * \param item item that was dropped
    *
    * This method is called by the base class when a packet is dropped because
    * the queue is full and by the subclasses to notify parent (this class) that
    * a packet has been dropped for other reasons.
    */
-  void Drop (Ptr<Packet> p);
+  void Drop (Ptr<QueueItem> item);
 
 private:
   /**
@@ -219,6 +231,12 @@ private:
    */
   virtual Ptr<const QueueItem> DoPeek (void) const = 0;
 
+  /**
+   *  \brief Notification of a packet drop
+   *  \param item item that was dropped
+   */
+  void NotifyDrop (Ptr<QueueItem> item);
+
   /// Traced callback: fired when a packet is enqueued
   TracedCallback<Ptr<const Packet> > m_traceEnqueue;
   /// Traced callback: fired when a packet is dequeued
@@ -236,6 +254,7 @@ private:
   uint32_t m_maxPackets;              //!< max packets in the queue
   uint32_t m_maxBytes;                //!< max bytes in the queue
   QueueMode m_mode;                   //!< queue mode (packets or bytes limited)
+  DropCallback m_dropCallback;        //!< drop callback
 };
 
 } // namespace ns3

src/traffic-control/model/codel-queue-disc.cc

@@ -296,13 +296,16 @@ CoDelQueueDisc::DoEnqueue (Ptr<QueueDiscItem> item)
   // Tag packet with current time for DoDequeue() to compute sojourn time
   CoDelTimestampTag tag;
   p->AddPacketTag (tag);
-  
-  GetInternalQueue (0)->Enqueue (item);
+
+  bool retval = GetInternalQueue (0)->Enqueue (item);
+
+  // If Queue::Enqueue fails, QueueDisc::Drop is called by the internal queue
+  // because QueueDisc::AddInternalQueue sets the drop callback
 
   NS_LOG_LOGIC ("Number packets " << GetInternalQueue (0)->GetNPackets ());
   NS_LOG_LOGIC ("Number bytes " << GetInternalQueue (0)->GetNBytes ());
 
-  return true;
+  return retval;
 }
 
 bool

src/traffic-control/model/pfifo-fast-queue-disc.cc

@@ -87,15 +87,14 @@ PfifoFastQueueDisc::DoEnqueue (Ptr<QueueDiscItem> item)
       band = ret;
     }
 
-  if (!GetInternalQueue(band)->Enqueue (item))
-    {
-      NS_LOG_LOGIC ("Enqueue failed -- dropping pkt");
-      Drop (item);
-      return false;
-    }
+  bool retval = GetInternalQueue(band)->Enqueue (item);
+
+  // If Queue::Enqueue fails, QueueDisc::Drop is called by the internal queue
+  // because QueueDisc::AddInternalQueue sets the drop callback
+
   NS_LOG_LOGIC ("Number packets band " << band << ": " << GetInternalQueue(band)->GetNPackets ());
 
-  return true;
+  return retval;
 }
 
 Ptr<QueueDiscItem>

src/traffic-control/model/queue-disc.cc

@@ -313,6 +313,9 @@ void
 QueueDisc::AddInternalQueue (Ptr<Queue> queue)
 {
   NS_LOG_FUNCTION (this);
+  // set the drop callback on the internal queue, so that the queue disc is
+  // notified of packets dropped by the internal queue
+  queue->SetDropCallback (MakeCallback (&QueueDisc::Drop, this));
   m_queues.push_back (queue);
 }
 

src/traffic-control/model/red-queue-disc.cc

@@ -410,12 +410,15 @@ RedQueueDisc::DoEnqueue (Ptr<QueueDiscItem> item)
       return false;
     }
 
-  GetInternalQueue (0)->Enqueue (item);
+  bool retval = GetInternalQueue (0)->Enqueue (item);
+
+  // If Queue::Enqueue fails, QueueDisc::Drop is called by the internal queue
+  // because QueueDisc::AddInternalQueue sets the drop callback
 
   NS_LOG_LOGIC ("Number packets " << GetInternalQueue (0)->GetNPackets ());
   NS_LOG_LOGIC ("Number bytes " << GetInternalQueue (0)->GetNBytes ());
 
-  return true;
+  return retval;
 }
 
 /*