rlc v2: improve buffer status reporting

The old method was wrong.
The new method is better, but not accurate, especially when the
TX buffer contains SDU of size > 2047 bytes.

Plus it's probably too slow.

To be refined at some point.

openair2/LAYER2/rlc_v2/rlc_entity_am.c

@@ -1394,10 +1394,15 @@ rlc_entity_buffer_status_t rlc_entity_am_buffer_status(
     ret.status_size = 0;
 
   /* TX PDU */
+  /* todo: if an SDU has size >2047 in the tx list then processing
+   * stops and computed size will not be accurate. Change the computation
+   * to be more accurate (if needed).
+   */
   tx_size = compute_new_pdu_size(entity, maxsize);
   ret.tx_size = tx_size.data_size + tx_size.header_size;
 
   /* reTX PDU */
+  /* todo: report size of all available data, not just first PDU */
   ret.retx_size = retx_pdu_size(entity, maxsize);
 
   return ret;

openair2/LAYER2/rlc_v2/rlc_entity_um.c

@@ -407,6 +407,10 @@ rlc_entity_buffer_status_t rlc_entity_um_buffer_status(
 
   ret.status_size = 0;
 
+  /* todo: if an SDU has size >2047 in the tx list then processing
+   * stops and computed size will not be accurate. Change the computation
+   * to be more accurate (if needed).
+   */
   tx_size = tx_pdu_size(entity, maxsize);
   ret.tx_size = tx_size.data_size + tx_size.header_size;
 

openair2/LAYER2/rlc_v2/rlc_oai_api.c

@@ -170,13 +170,14 @@ mac_rlc_status_resp_t mac_rlc_status_ind(
   if (rb != NULL) {
     rlc_entity_buffer_status_t buf_stat;
     rb->set_time(rb, rlc_current_time);
-    buf_stat = rb->buffer_status(rb, tb_sizeP ? tb_sizeP : 1000000);
-    if (buf_stat.status_size)
-      ret.bytes_in_buffer = buf_stat.status_size;
-    else if (buf_stat.retx_size)
-      ret.bytes_in_buffer = buf_stat.retx_size;
-    else
-      ret.bytes_in_buffer = buf_stat.tx_size;
+    /* 36.321 deals with BSR values up to 3000000 bytes, after what it
+     * reports '> 3000000' (table 6.1.3.1-2). Passing 4000000 is thus
+     * more than enough.
+     */
+    buf_stat = rb->buffer_status(rb, 4000000);
+    ret.bytes_in_buffer = buf_stat.status_size
+                        + buf_stat.retx_size
+                        + buf_stat.tx_size;
     ue->saved_status_ind_tb_size[channel_idP - 1] = tb_sizeP;
   } else {
     ret.bytes_in_buffer = 0;