Refactor nr_sdap_qfi2drb_map

The goal of this function is to return the DRB ID mapped to the input QFI, for both DL and UL.
The function looks up the DRB that is mapped to the QFI, if no mapping rule exists
returns the default DRB. Returns 0 If no mapping and no default DRB exists for that QFI

The function should not update the stored mapping rules, that is done when receiving
a new SDAP configuration. In this function it was removed.

See TS 37.324, 5.2.1 Uplink
> If there is no stored QoS flow to DRB mapping rule for the QoS flow as specified in the subclause 5.3,
> map the SDAP SDU to the default DRB else, map the SDAP SDU to the DRB according to the stored QoS flow to DRB mapping rule.

openair2/SDAP/nr_sdap/nr_sdap_entity.c

@@ -357,27 +357,33 @@ void nr_sdap_qfi2drb_map_del(nr_sdap_entity_t *entity, uint8_t qfi){
 }
 
 /**
- * @brief   maps the QFIs to the default DRB if not mapping rule exists
- * @return  DRB that is mapped to the QFI, 0 if no mapping and no default DRB exists for that QFI
-*/
-rb_id_t nr_sdap_qfi2drb_map(nr_sdap_entity_t *entity, uint8_t qfi){
-  rb_id_t pdcp_entity;
-
-  pdcp_entity = entity->qfi2drb_table[qfi].drb_id;
-
-  if(pdcp_entity){
-    LOG_D(SDAP, "Mapping rule exists for QFI: %u\n", qfi);
-    return pdcp_entity;
-  } else if(entity->default_drb) {
-    LOG_D(SDAP, "Mapping QFI: %u to Default DRB: %ld\n", qfi, entity->default_drb);
-    entity->qfi2drb_map_update(entity, qfi, entity->default_drb, entity->qfi2drb_table[qfi].has_sdap_rx, entity->qfi2drb_table[qfi].has_sdap_tx);
+ * @brief   get the DRB ID mapped to the QFI, for both DL and UL
+ * @return  DRB that is mapped to the QFI
+ *          or the default DRB if no mapping rule exists
+ *          or 0 if no mapping and no default DRB exists for that QFI
+ * @ref     TS 37.324, 5.2.1 Uplink
+ *          If there is no stored QoS flow to DRB mapping rule for the
+ *          QoS flow as specified in the subclause 5.3, and a default DRB is configured,
+ *          map the SDAP SDU to the default DRB else, map the SDAP SDU to the DRB according
+ *          to the stored QoS flow to DRB mapping rule. */
+static int nr_sdap_qfi2drb(nr_sdap_entity_t *entity, uint8_t qfi)
+{
+  /* Fetch DRB ID mapped to QFI */
+  int drb_id = entity->qfi2drb_table[qfi].drb_id;
+  if (drb_id) {
+    /* QoS flow to DRB mapping rule exists, return corresponding DRB ID */
+    LOG_D(SDAP, "Existing QoS flow to DRB mapping rule: QFI %u to DRB %d\n", qfi, drb_id);
+    return drb_id;
+  } else if (entity->default_drb) {
+    /* QoS flow to DRB mapping rule does not exist, map SDAP SDU to default DRB, e.g. return default DRB of the SDAP entity */
+    LOG_D(SDAP, "QoS flow to DRB mapping rule does not exists! mapping SDU to Default DRB: %ld\n", entity->default_drb);
     return entity->default_drb;
   } else {
-    LOG_D(SDAP, "Mapping rule and default DRB do not exist for QFI:%u\n", qfi);
+    /* Note: UE undefined behaviour when neither a default DRB
+       nor a stored QoS flow to DRB mapping rule exists */
+    LOG_E(SDAP, "Mapping rule and default DRB do not exist for QFI:%u\n", qfi);
     return SDAP_MAP_RULE_EMPTY;
   }
-
-  return pdcp_entity;
 }
 
 nr_sdap_ul_hdr_t nr_sdap_construct_ctrl_pdu(uint8_t qfi){
@@ -508,7 +514,7 @@ nr_sdap_entity_t *new_nr_sdap_entity(const int is_gnb, const ue_id_t ue_id, cons
   // QFI to DRB mapping functions pointers
   sdap_entity->qfi2drb_map_update = nr_sdap_qfi2drb_map_update;
   sdap_entity->qfi2drb_map_delete = nr_sdap_qfi2drb_map_del;
-  sdap_entity->qfi2drb_map = nr_sdap_qfi2drb_map;
+  sdap_entity->qfi2drb_map = nr_sdap_qfi2drb;
   sdap_entity->pdusession_sock = -1;
 
   // set default DRB

openair2/SDAP/nr_sdap/nr_sdap_entity.h

@@ -105,7 +105,7 @@ typedef struct nr_sdap_entity_s {
 
   void (*qfi2drb_map_update)(struct nr_sdap_entity_s *entity, uint8_t qfi, rb_id_t drb, bool has_sdap_rx, bool has_sdap_tx);
   void (*qfi2drb_map_delete)(struct nr_sdap_entity_s *entity, uint8_t qfi);
-  rb_id_t (*qfi2drb_map)(struct nr_sdap_entity_s *entity, uint8_t qfi);
+  int (*qfi2drb_map)(struct nr_sdap_entity_s *entity, uint8_t qfi);
 
   nr_sdap_ul_hdr_t (*sdap_construct_ctrl_pdu)(uint8_t qfi);
   rb_id_t (*sdap_map_ctrl_pdu)(struct nr_sdap_entity_s *entity, rb_id_t pdcp_entity, int map_type, uint8_t dl_qfi);
@@ -144,17 +144,6 @@ void nr_sdap_qfi2drb_map_update(nr_sdap_entity_t *entity, uint8_t qfi, rb_id_t d
 /* QFI to DRB Mapping Related Function */
 void nr_sdap_qfi2drb_map_del(nr_sdap_entity_t *entity, uint8_t qfi);
 
-/*
- * TS 37.324
- * 4.4 Functions
- * Mapping between a QoS flow and a DRB for both DL and UL.
- *
- * 5.2.1 Uplink
- * If there is no stored QoS flow to DRB mapping rule for the QoS flow as specified in the subclause 5.3, map the SDAP SDU to the default DRB
- * else, map the SDAP SDU to the DRB according to the stored QoS flow to DRB mapping rule.
- */
-rb_id_t nr_sdap_qfi2drb_map(nr_sdap_entity_t *entity, uint8_t qfi);
-
 /*
  * TS 37.324 5.3 QoS flow to DRB Mapping 
  * construct an end-marker control PDU, as specified in the subclause 6.2.3, for the QoS flow;