gsmtap-rlp: Add support for skipping generating NULL frameslaforge/csd_gsmtap

If there's nothing to transmit over a CSD NT channel, both ends generate
NULL frames.  Let's add an option to suppress GSMTAP output for those,
creating pcap files with less noise.

Change-Id: I85a2159cfaa01bfb4205c1462e3a9dbda68e4bad

4 files changed, 23 insertions, 4 deletions

diff --git a/TODO-RELEASE b/TODO-RELEASE
index 1ed7b53d..2bbfab59 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -8,3 +8,4 @@
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what	        description / commit summary line
 libosmogsm	>1.9.0		added new PRIM_INFO to include/osmocom/gsm/l1sap.h
+libosmogsm	>1.9.0		use of RLP code in libosmogsm
diff --git a/include/osmo-bts/bts.h b/include/osmo-bts/bts.h
index f9ddb1e9..8f1f1ab6 100644
--- a/include/osmo-bts/bts.h
+++ b/include/osmo-bts/bts.h
@@ -378,6 +378,7 @@ struct gsm_bts {
 		uint32_t sapi_mask;
 		uint8_t sapi_acch;
 		bool rlp;
+		bool rlp_skip_null;
 	} gsmtap;
 
 	struct osmux_state osmux;
diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index ece18e04..7c60d70e 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -33,6 +33,7 @@
 #include <osmocom/gsm/l1sap.h>
 #include <osmocom/gsm/gsm_utils.h>
 #include <osmocom/gsm/rsl.h>
+#include <osmocom/gsm/rlp.h>
 #include <osmocom/core/gsmtap.h>
 #include <osmocom/core/gsmtap_util.h>
 #include <osmocom/core/utils.h>
@@ -1848,6 +1849,7 @@ static void gsmtap_csd_rlp_process(struct gsm_lchan *lchan, bool is_uplink,
 {
 	struct gsm_bts_trx *trx = lchan->ts->trx;
 	struct gsmtap_inst *inst = trx->bts->gsmtap.inst;
+	struct osmo_rlp_frame_decoded rlpf;
 	pbit_t *rlp_buf;
 	int byte_len;
 
@@ -1898,6 +1900,12 @@ static void gsmtap_csd_rlp_process(struct gsm_lchan *lchan, bool is_uplink,
 		byte_len = osmo_ubit2pbit_ext(rlp_buf, 0, data, 0, data_len, 1);
 	}
 
+	if (trx->bts->gsmtap.rlp_skip_null) {
+		int rc = osmo_rlp_decode(&rlpf, 0, rlp_buf, byte_len);
+		if (rc == 0 && rlpf.ftype == OSMO_RLP_FT_U && rlpf.u_ftype == OSMO_RLP_U_FT_NULL)
+			return;
+	}
+
 	gsmtap_send_ex(inst, GSMTAP_TYPE_GSM_RLP, trx->arfcn | is_uplink ? GSMTAP_ARFCN_F_UPLINK : 0,
 		       lchan->ts->nr,
 		       lchan->type == GSM_LCHAN_TCH_H ? GSMTAP_CHANNEL_VOICE_H : GSMTAP_CHANNEL_VOICE_F,
diff --git a/src/common/vty.c b/src/common/vty.c
index b5ab132c..2bc5bf8f 100644
--- a/src/common/vty.c
+++ b/src/common/vty.c
@@ -447,8 +447,12 @@ static void config_write_bts_single(struct vty *vty, const struct gsm_bts *bts)
 		sapi_buf = osmo_str_tolower(get_value_string(gsmtap_sapi_names, GSMTAP_CHANNEL_ACCH));
 		vty_out(vty, " gsmtap-sapi %s%s", sapi_buf, VTY_NEWLINE);
 	}
-	if (bts->gsmtap.rlp)
-		vty_out(vty, " gsmtap-rlp%s", VTY_NEWLINE);
+	if (bts->gsmtap.rlp) {
+		if (bts->gsmtap.rlp_skip_null)
+			vty_out(vty, " gsmtap-rlp skip-null%s", VTY_NEWLINE);
+		else
+			vty_out(vty, " gsmtap-rlp%s", VTY_NEWLINE);
+	}
 	vty_out(vty, " min-qual-rach %d%s", bts->min_qual_rach,
 		VTY_NEWLINE);
 	vty_out(vty, " min-qual-norm %d%s", bts->min_qual_norm,
@@ -2389,11 +2393,16 @@ DEFUN(cfg_bts_no_gsmtap_sapi, cfg_bts_no_gsmtap_sapi_cmd,
 }
 
 DEFUN(cfg_bts_gsmtap_rlp, cfg_bts_gsmtap_rlp_cmd,
-	"gsmtap-rlp",
-	"Enable generation of GSMTAP frames for RLP (non-transparent CSD)\n")
+	"gsmtap-rlp [skip-null]",
+	"Enable generation of GSMTAP frames for RLP (non-transparent CSD)\n"
+	"Skip the generation of GSMTAP for RLP NULL frames\n")
 {
 	struct gsm_bts *bts = vty->index;
 	bts->gsmtap.rlp = true;
+	if (argc >= 1 && !strcmp(argv[0], "skip-null"))
+		bts->gsmtap.rlp_skip_null = true;
+	else
+		bts->gsmtap.rlp_skip_null = false;
 	return CMD_SUCCESS;
 }