enb_stack_lte: implement the PDCP interface for GTPU on the stack

this prepares for a change in which GTPU no longer writes into PDCP
directly but instead uses the stack as a wrapper.

For this the interface will be changed to use the EPS bearer ID instead
of the LCID

The stack will know which PDCP entity (EUTRA or NR) is currently associated
with the EPS bearer ID and will forward the PDU accordingly.

srsenb/hdr/stack/enb_stack_lte.h

@@ -38,6 +38,7 @@ namespace srsenb {
 class enb_stack_lte final : public enb_stack_base,
                             public stack_interface_phy_lte,
                             public stack_interface_phy_nr,
+                            public pdcp_interface_gtpu,
                             public srsran::thread
 {
 public:
@@ -132,6 +133,10 @@ public:
   }
   void rach_detected(const rach_info_t& rach_info) override { mac_nr.rach_detected(rach_info); }
 
+  // pdcp_interface_gtpu
+  void write_sdu(uint16_t rnti, uint32_t lcid, srsran::unique_byte_buffer_t sdu, int pdcp_sn = -1) override;
+  std::map<uint32_t, srsran::unique_byte_buffer_t> get_buffered_pdus(uint16_t rnti, uint32_t lcid) override;
+
 private:
   static const int STACK_MAIN_THREAD_PRIO = 4;
   // thread loop

srsenb/src/stack/enb_stack_lte.cc

@@ -187,7 +187,7 @@ int enb_stack_lte::init(const stack_args_t& args_, const rrc_cfg_t& rrc_cfg_)
   gtpu_args.mme_addr                     = args.s1ap.mme_addr;
   gtpu_args.gtp_bind_addr                = args.s1ap.gtp_bind_addr;
   gtpu_args.indirect_tunnel_timeout_msec = args.gtpu_indirect_tunnel_timeout_msec;
-  if (gtpu.init(gtpu_args, &pdcp) != SRSRAN_SUCCESS) {
+  if (gtpu.init(gtpu_args, this) != SRSRAN_SUCCESS) {
     stack_logger.error("Couldn't initialize GTPU");
     return SRSRAN_ERROR;
   }
@@ -278,4 +278,17 @@ void enb_stack_lte::run_thread()
   }
 }
 
+void enb_stack_lte::write_sdu(uint16_t                     rnti,
+                              uint32_t                     lcid /* to be replaced with eps_bearer_id */,
+                              srsran::unique_byte_buffer_t sdu,
+                              int                          pdcp_sn)
+{
+  pdcp.write_sdu(rnti, lcid, std::move(sdu), pdcp_sn);
+}
+
+std::map<uint32_t, srsran::unique_byte_buffer_t> enb_stack_lte::get_buffered_pdus(uint16_t rnti, uint32_t lcid)
+{
+  return pdcp.get_buffered_pdus(rnti, lcid);
+}
+
 } // namespace srsenb