nr,mac_sch_pdu,mux: fix packing of MAC subPDUs with 16bit L field

the created RLC PDU was too large to fit inside the MAC grant
because only the header room for the short L field was used.

The patch determines the correct size before passing the opportunity to RLC.

It also improves logging in error case by using the MAC logger instead of
stderr/stdout when error occurs.

lib/include/srsran/mac/mac_sch_pdu_nr.h

@@ -51,7 +51,10 @@ public:
     PADDING = 0b111111,
   } nr_lcid_sch_t;
 
-  mac_sch_subpdu_nr(mac_sch_pdu_nr* parent_);
+  // SDUs up to 256 B can use the short 8-bit L field
+  static const int32_t MAC_SUBHEADER_LEN_THRESHOLD = 256;
+
+  mac_sch_subpdu_nr(mac_sch_pdu_nr* parent_) : parent(parent_), logger(&srslog::fetch_basic_logger("MAC")){};
 
   nr_lcid_sch_t get_type();
   bool          is_sdu();
@@ -100,7 +103,8 @@ public:
   static uint32_t sizeof_ce(uint32_t lcid, bool is_ul);
 
 private:
-  // protected:
+  srslog::basic_logger* logger;
+
   uint32_t lcid          = 0;
   int      header_length = 0;
   int      sdu_length    = 0;

lib/src/mac/mac_sch_pdu_nr.cc

@@ -14,8 +14,6 @@
 
 namespace srsran {
 
-mac_sch_subpdu_nr::mac_sch_subpdu_nr(mac_sch_pdu_nr* parent_) : parent(parent_) {}
-
 mac_sch_subpdu_nr::nr_lcid_sch_t mac_sch_subpdu_nr::get_type()
 {
   if (lcid >= 32) {
@@ -85,11 +83,11 @@ void mac_sch_subpdu_nr::set_sdu(const uint32_t lcid_, const uint8_t* payload_, c
     F_bit      = false;
     sdu_length = sizeof_ce(lcid, parent->is_ulsch());
     if (len_ != static_cast<uint32_t>(sdu_length)) {
-      srslog::fetch_basic_logger("MAC").warning("Invalid SDU length of UL-SCH SDU (%d != %d)", len_, sdu_length);
+      logger->warning("Invalid SDU length of UL-SCH SDU (%d != %d)", len_, sdu_length);
     }
   }
 
-  if (sdu_length >= 256) {
+  if (sdu_length >= MAC_SUBHEADER_LEN_THRESHOLD) {
     F_bit = true;
     header_length += 1;
   }
@@ -160,7 +158,7 @@ uint32_t mac_sch_subpdu_nr::write_subpdu(const uint8_t* start_)
   } else if (header_length == 1) {
     // do nothing
   } else {
-    srslog::fetch_basic_logger("MAC").warning("Error while packing PDU. Unsupported header length (%d)", header_length);
+    logger->error("Error while packing PDU. Unsupported header length (%d)", header_length);
   }
 
   // copy SDU payload
@@ -301,7 +299,7 @@ void mac_sch_pdu_nr::unpack(const uint8_t* payload, const uint32_t& len)
   while (offset < len) {
     mac_sch_subpdu_nr sch_pdu(this);
     if (sch_pdu.read_subheader(payload + offset) == SRSRAN_ERROR) {
-      fprintf(stderr, "Error parsing NR MAC PDU (len=%d, offset=%d)\n", len, offset);
+      logger.error("Error parsing NR MAC PDU (len=%d, offset=%d)\n", len, offset);
       return;
     }
     offset += sch_pdu.get_total_length();
@@ -314,7 +312,7 @@ void mac_sch_pdu_nr::unpack(const uint8_t* payload, const uint32_t& len)
     subpdus.push_back(sch_pdu);
   }
   if (offset != len) {
-    fprintf(stderr, "Error parsing NR MAC PDU (len=%d, offset=%d)\n", len, offset);
+    logger.error("Error parsing NR MAC PDU (len=%d, offset=%d)\n", len, offset);
   }
 }
 
@@ -373,7 +371,7 @@ uint32_t mac_sch_pdu_nr::add_sdu(const uint32_t lcid_, const uint8_t* payload_,
 {
   int header_size = size_header_sdu(lcid_, len_);
   if (header_size + len_ > remaining_len) {
-    printf("Header and SDU exceed space in PDU (%d > %d).\n", header_size + len_, remaining_len);
+    logger.error("Header and SDU exceed space in PDU (%d + %d > %d)", header_size, len_, remaining_len);
     return SRSRAN_ERROR;
   }
 

srsue/src/stack/mac_nr/mux_nr.cc

@@ -73,8 +73,13 @@ srsran::unique_byte_buffer_t mux_nr::get_pdu(uint32_t max_pdu_len)
         // read RLC PDU
         rlc_buff->clear();
         uint8_t* rd = rlc_buff->msg;
-        int      pdu_len = 0;
+
-        pdu_len          = rlc->read_pdu(lc.lcid, rd, tx_pdu.get_remaing_len() - 2);
+        // Determine space for RLC
+        uint32_t rlc_opportunity = tx_pdu.get_remaing_len();
+        rlc_opportunity -= tx_pdu.get_remaing_len() >= srsran::mac_sch_subpdu_nr::MAC_SUBHEADER_LEN_THRESHOLD ? 3 : 2;
+
+        // Read PDU from RLC
+        int pdu_len = rlc->read_pdu(lc.lcid, rd, rlc_opportunity);
 
         // Add SDU if RLC has something to tx
         if (pdu_len > 0) {
@@ -84,6 +89,7 @@ srsran::unique_byte_buffer_t mux_nr::get_pdu(uint32_t max_pdu_len)
           // add to MAC PDU and pack
           if (tx_pdu.add_sdu(lc.lcid, rlc_buff->msg, rlc_buff->N_bytes) != SRSRAN_SUCCESS) {
             logger.error("Error packing MAC PDU");
+            break;
           }
         } else {
           break;