wifi: Pass the TXOP holder to EHT FEM TxopEnd()

because TxopEnd() may be called when the TXOP holder has been already
reset, e.g., when a TXOP is terminated with a CF-End frame

src/wifi/model/eht/eht-frame-exchange-manager.cc

@@ -840,7 +840,8 @@ EhtFrameExchangeManager::PostProcessFrame(Ptr<const WifiPsdu> psdu, const WifiTx
             auto delay =
                 m_phy->GetSifs() + m_phy->GetSlot() + MicroSeconds(RX_PHY_START_DELAY_USEC);
             NS_LOG_DEBUG("Expected TXOP end=" << (Simulator::Now() + delay).As(Time::S));
-            m_ongoingTxopEnd = Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this);
+            m_ongoingTxopEnd =
+                Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this, m_txopHolder);
         }
         else
         {
@@ -991,7 +992,8 @@ EhtFrameExchangeManager::ReceiveMpdu(Ptr<const WifiMpdu> mpdu,
             NS_LOG_DEBUG("Expected TXOP end=" << (Simulator::Now() + m_phy->GetSifs()).As(Time::S));
             m_ongoingTxopEnd = Simulator::Schedule(m_phy->GetSifs() + NanoSeconds(1),
                                                    &EhtFrameExchangeManager::TxopEnd,
-                                                   this);
+                                                   this,
+                                                   hdr.GetAddr2());
         }
     }
 
@@ -1015,9 +1017,9 @@ EhtFrameExchangeManager::ReceiveMpdu(Ptr<const WifiMpdu> mpdu,
 }
 
 void
-EhtFrameExchangeManager::TxopEnd()
+EhtFrameExchangeManager::TxopEnd(const std::optional<Mac48Address>& txopHolder)
 {
-    NS_LOG_FUNCTION(this);
+    NS_LOG_FUNCTION(this << txopHolder.has_value());
 
     if (m_phy->IsReceivingPhyHeader())
     {
@@ -1028,19 +1030,19 @@ EhtFrameExchangeManager::TxopEnd()
         NS_LOG_DEBUG("PHY is decoding the PHY header of PPDU, postpone TXOP end");
         m_ongoingTxopEnd = Simulator::Schedule(MicroSeconds(WAIT_FOR_RXSTART_DELAY_USEC),
                                                &EhtFrameExchangeManager::TxopEnd,
-                                               this);
+                                               this,
+                                               txopHolder);
         return;
     }
 
     if (m_staMac && m_staMac->IsEmlsrLink(m_linkId))
     {
         m_staMac->GetEmlsrManager()->NotifyTxopEnd(m_linkId);
     }
-    else if (m_apMac && m_txopHolder &&
-             GetWifiRemoteStationManager()->GetEmlsrEnabled(*m_txopHolder))
+    else if (m_apMac && txopHolder && GetWifiRemoteStationManager()->GetEmlsrEnabled(*txopHolder))
     {
         // EMLSR client terminated its TXOP and is back to listening operation
-        EmlsrSwitchToListening(*m_txopHolder, Seconds(0));
+        EmlsrSwitchToListening(*txopHolder, Seconds(0));
     }
 }
 
@@ -1083,7 +1085,8 @@ EhtFrameExchangeManager::UpdateTxopEndOnTxStart(Time txDuration, Time durationId
     }
 
     NS_LOG_DEBUG("Expected TXOP end=" << (Simulator::Now() + delay).As(Time::S));
-    m_ongoingTxopEnd = Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this);
+    m_ongoingTxopEnd =
+        Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this, m_txopHolder);
 }
 
 void
@@ -1101,8 +1104,10 @@ EhtFrameExchangeManager::UpdateTxopEndOnRxStartIndication(Time psduDuration)
     m_ongoingTxopEnd.Cancel();
 
     NS_LOG_DEBUG("Expected TXOP end=" << (Simulator::Now() + psduDuration).As(Time::S));
-    m_ongoingTxopEnd =
-        Simulator::Schedule(psduDuration + NanoSeconds(1), &EhtFrameExchangeManager::TxopEnd, this);
+    m_ongoingTxopEnd = Simulator::Schedule(psduDuration + NanoSeconds(1),
+                                           &EhtFrameExchangeManager::TxopEnd,
+                                           this,
+                                           m_txopHolder);
 }
 
 void
@@ -1123,15 +1128,16 @@ EhtFrameExchangeManager::UpdateTxopEndOnRxEnd(Time durationId)
     if (durationId <= m_phy->GetSifs())
     {
         NS_LOG_DEBUG("Assume TXOP ended based on Duration/ID value");
-        TxopEnd();
+        TxopEnd(m_txopHolder);
         return;
     }
 
     // we may send a response after a SIFS or we may receive another frame after a SIFS.
     // Postpone the TXOP end by considering the latter (which takes longer)
     auto delay = m_phy->GetSifs() + m_phy->GetSlot() + MicroSeconds(RX_PHY_START_DELAY_USEC);
     NS_LOG_DEBUG("Expected TXOP end=" << (Simulator::Now() + delay).As(Time::S));
-    m_ongoingTxopEnd = Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this);
+    m_ongoingTxopEnd =
+        Simulator::Schedule(delay, &EhtFrameExchangeManager::TxopEnd, this, m_txopHolder);
 }
 
 } // namespace ns3

src/wifi/model/eht/eht-frame-exchange-manager.h

@@ -156,8 +156,10 @@ class EhtFrameExchangeManager : public HeFrameExchangeManager
 
     /**
      * Take actions when a TXOP (of which we are not the holder) ends.
+     *
+     * \param txopHolder the holder of the TXOP (if any)
      */
-    void TxopEnd();
+    void TxopEnd(const std::optional<Mac48Address>& txopHolder);
 
     EventId m_ongoingTxopEnd; //!< event indicating the possible end of the current TXOP (of which
                               //!< we are not the holder)

src/wifi/test/wifi-emlsr-test.cc

@@ -1483,30 +1483,30 @@ EmlsrDlTxopTest::CheckResults()
      */
 
     // for each EMLSR client, there should be a frame exchange with ICF and no data frame
-    // (ICF protects the EML Notification response) and two frame exchanges with data frames
+    // (ICF protects the EML Notification response) if the EML Notification response is sent
+    // while EMLSR mode is still enabled and two frame exchanges with data frames
     for (std::size_t i = 0; i < m_nEmlsrStations; i++)
     {
         // the default EMLSR Manager requests to send EML Notification frames on the link where
-        // the main PHY is operating, hence this link is an EMLSR link and the EML Notification
-        // frame is protected by an ICF
+        // the main PHY is operating; if EMLSR mode is still enabled on this link when the AP MLD
+        // sends the EML Notification response, the latter is protected by an ICF
         auto exchangeIt = frameExchanges.at(i).cbegin();
 
         auto linkIdOpt = m_staMacs[i]->GetLinkForPhy(m_mainPhyId);
         NS_TEST_ASSERT_MSG_EQ(linkIdOpt.has_value(),
                               true,
                               "Didn't find a link on which the main PHY is operating");
 
-        NS_TEST_EXPECT_MSG_EQ(IsTrigger(exchangeIt->front()->psduMap),
-                              true,
-                              "Expected an MU-RTS TF as ICF of first frame exchange sequence");
-        NS_TEST_EXPECT_MSG_EQ(+exchangeIt->front()->linkId,
-                              +linkIdOpt.value(),
-                              "ICF was not sent on the expected link");
-        NS_TEST_EXPECT_MSG_EQ(exchangeIt->size(),
-                              1,
-                              "Expected no data frame in the first frame exchange sequence");
-
-        frameExchanges.at(i).pop_front();
+        if (IsTrigger(exchangeIt->front()->psduMap))
+        {
+            NS_TEST_EXPECT_MSG_EQ(+exchangeIt->front()->linkId,
+                                  +linkIdOpt.value(),
+                                  "ICF was not sent on the expected link");
+            NS_TEST_EXPECT_MSG_EQ(exchangeIt->size(),
+                                  1,
+                                  "Expected no data frame in the first frame exchange sequence");
+            frameExchanges.at(i).pop_front();
+        }
 
         NS_TEST_EXPECT_MSG_GT_OR_EQ(frameExchanges.at(i).size(),
                                     2,