gsm_abis_om2000: Introduce expert info for unusual situations

In OM2000, it is not usual to receive NACK, REJECT or "performed not
according to request" type messages.  Let's highlight them using expert
info as a convenience to the user.

Change-Id: I47b865c32fd9ec82ec63699babd31f3849f3006c
Reviewed-on: https://code.wireshark.org/review/18453
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

1 files changed, 39 insertions, 7 deletions

diff --git a/epan/dissectors/packet-gsm_abis_om2000.c b/epan/dissectors/packet-gsm_abis_om2000.c
index 457977568e..9fb57ec0b3 100644
--- a/epan/dissectors/packet-gsm_abis_om2000.c
+++ b/epan/dissectors/packet-gsm_abis_om2000.c
@@ -29,6 +29,7 @@
 #include "config.h"
 
 #include <epan/packet.h>
+#include <epan/expert.h>
 
 void proto_register_abis_om2000(void);
 
@@ -122,6 +123,10 @@ static int ett_om2k_isl = -1;
 static int ett_om2k_conl = -1;
 static int ett_om2k_iwd = -1;
 
+static expert_field ei_om2k_not_performed = EI_INIT;
+static expert_field ei_om2k_reject = EI_INIT;
+static expert_field ei_om2k_nack = EI_INIT;
+
 static const value_string om2k_msgcode_vals[] = {
 	{ 0x0000, "Abort SP Command" },
 	{ 0x0002, "Abort SP Complete" },
@@ -790,16 +795,20 @@ dissect_om2k_negotiation_record2(tvbuff_t *tvb, gint base_offset, proto_tree *tr
 
 
 static gint
-dissect_om2k_attrs(tvbuff_t *tvb, gint offset, proto_tree *tree)
+dissect_om2k_attrs(tvbuff_t *tvb, packet_info *pinfo, gint offset, proto_tree *tree)
 {
 	while (tvb_reported_length_remaining(tvb, offset) > 0) {
 		guint8 iei = tvb_get_guint8(tvb, offset++);
 		guint8 len, tmp;
+		proto_item *ti;
 
 		switch (iei) {
 		case 0x00: /* Accordance Information */
-			proto_tree_add_item(tree, hf_om2k_aip, tvb,
-					    offset++, 1, ENC_BIG_ENDIAN);
+			tmp = tvb_get_guint8(tvb, offset);
+			ti = proto_tree_add_item(tree, hf_om2k_aip, tvb,
+						 offset++, 1, ENC_BIG_ENDIAN);
+			if (tmp != 0x00)
+				expert_add_info(pinfo, ti, &ei_om2k_not_performed);
 			break;
 		case 0x06: /* BCC */
 			proto_tree_add_item(tree, hf_om2k_bcc, tvb,
@@ -1150,6 +1159,7 @@ dissect_abis_om2000(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* d
 	proto_tree *om2k_tree;
 	guint16     msg_code;
 	guint8      tmp;
+	const gchar *msgt_str;
 
 	int offset;
 
@@ -1176,9 +1186,8 @@ dissect_abis_om2000(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* d
 	if (tree == NULL)
 		return tvb_captured_length(tvb);   /* No refs to COL_...  beyond this point */
 
-	proto_item_append_text(ti, " %s ",
-			       val_to_str_ext(msg_code, &om2k_msgcode_vals_ext,
-					  "unknown 0x%04x"));
+	msgt_str = val_to_str_ext(msg_code, &om2k_msgcode_vals_ext, "unknown 0x%04x");
+	proto_item_append_text(ti, " %s ", msgt_str);
 
 	switch (msg_code) {
 	case 0x74: /* Operational Info */
@@ -1203,7 +1212,13 @@ dissect_abis_om2000(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* d
 	default:
 		break;
 	}
-	dissect_om2k_attrs(tvb, offset, om2k_tree);
+
+	if (strstr(msgt_str, "Reject"))
+		expert_add_info(pinfo, ti, &ei_om2k_reject);
+	if (strstr(msgt_str, "NACK"))
+		expert_add_info(pinfo, ti, &ei_om2k_nack);
+
+	dissect_om2k_attrs(tvb, pinfo, offset, om2k_tree);
 	return tvb_captured_length(tvb);
 }
 
@@ -1611,11 +1626,28 @@ proto_register_abis_om2000(void)
 		&ett_om2k_conl,
 		&ett_om2k_iwd,
 	};
+	static ei_register_info ei[] = {
+		{ &ei_om2k_not_performed,
+		  { "gsm_abis_om2000.not_performed", PI_RESPONSE_CODE, PI_WARN,
+		    "Operation not performed as per request", EXPFILL }
+		},
+		{ &ei_om2k_reject,
+		  { "gsm_abis_om2000.reject", PI_RESPONSE_CODE, PI_WARN,
+		    "Operation Rejected by RBS", EXPFILL }
+		},
+		{ &ei_om2k_nack,
+		  { "gsm_abis_om2000.nack", PI_RESPONSE_CODE, PI_ERROR,
+		    "Operation NACKed by peer", EXPFILL }
+		},
+	};
+	expert_module_t *expert_om2000;
 
 	proto_abis_om2000 = proto_register_protocol("Ericsson A-bis OML",
 						    "Ericsson OML",
 						    "gsm_abis_om2000");
 
+	expert_om2000 = expert_register_protocol(proto_abis_om2000);
+	expert_register_field_array(expert_om2000, ei, array_length(ei));
 	proto_register_field_array(proto_abis_om2000, hf, array_length(hf));
 
 	proto_register_subtree_array(ett, array_length(ett));