Powerlink: New heuristic payload dissection

 Up until now, the heuristic dissector for epl allways passed the
 complete epl frame. Therefore a lot of information got passed,
 which was not needed, resulting in subdissectors to have to call
 the epl dissector again, if the epl data had to be dissected.

 This patch adds a second heuristic dissector (not breaking the
 way, the existing one is working), which only passes the payload
 of the epl frame to a sub-dissector, therefore reducing memory
 overhead and increasing dissection speed.

 Upd: Changes according to comments in patchset

Change-Id: I2ef309310f421f24d96dd1c188e188ccfa5935cd
Reviewed-on: https://code.wireshark.org/review/190
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>

1 files changed, 38 insertions, 37 deletions

diff --git a/epan/dissectors/packet-epl.c b/epan/dissectors/packet-epl.c
index d5d542e518..f7d94db766 100644
--- a/epan/dissectors/packet-epl.c
+++ b/epan/dissectors/packet-epl.c
@@ -63,6 +63,7 @@ void proto_reg_handoff_epl(void);
 
 /* Allow heuristic dissection */
 static heur_dissector_list_t heur_epl_subdissector_list;
+static heur_dissector_list_t heur_epl_data_subdissector_list;
 
 #if 0
 /* Container for tapping relevant data */
@@ -472,6 +473,8 @@ static value_string_ext epl_sdo_asnd_commands_ext = VALUE_STRING_EXT_INIT(epl_sd
 static const gchar* addr_str_cn  = " (Controlled Node)";
 static const gchar* addr_str_res = " (reserved)";
 
+static dissector_handle_t data_dissector = NULL;
+
 static gint dissect_epl_soc(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, gint offset);
 static gint dissect_epl_preq(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, gint offset);
 static gint dissect_epl_pres(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, guint8 epl_src, gint offset);
@@ -510,7 +513,6 @@ static gint hf_epl_preq_ea       = -1;
 static gint hf_epl_preq_rd       = -1;
 static gint hf_epl_preq_pdov     = -1;
 static gint hf_epl_preq_size     = -1;
-static gint hf_epl_preq_pl       = -1;
 
 static gint hf_epl_pres_stat_ms  = -1;
 static gint hf_epl_pres_stat_cs  = -1;
@@ -521,7 +523,6 @@ static gint hf_epl_pres_pr       = -1;
 static gint hf_epl_pres_rs       = -1;
 static gint hf_epl_pres_pdov     = -1;
 static gint hf_epl_pres_size     = -1;
-static gint hf_epl_pres_pl       = -1;
 
 static gint hf_epl_soa_stat_ms   = -1;
 static gint hf_epl_soa_stat_cs   = -1;
@@ -645,7 +646,6 @@ static gint hf_epl_asnd_sdo_cmd_data_size                    = -1;
 static gint hf_epl_asnd_sdo_cmd_data_padding                 = -1;
 static gint hf_epl_asnd_sdo_cmd_data_index                   = -1;
 static gint hf_epl_asnd_sdo_cmd_data_subindex                = -1;
-static gint hf_epl_asnd_sdo_cmd_data_data                    = -1;
 /*static gint hf_epl_asnd_sdo_cmd_data_response      = -1;*/
 
 static gint hf_epl_asnd_sdo_cmd_abort_code                   = -1;
@@ -896,6 +896,29 @@ decode_epl_address (guchar adr)
 }
 
 gint
+dissect_epl_payload ( proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, gint offset, gint len )
+{
+	gint off = 0;
+	tvbuff_t * payload_tvb = NULL;;
+
+	off = offset;
+
+	if (len > 0)
+	{
+		if ( data_dissector == NULL )
+			data_dissector = find_dissector ( "data" );
+
+		payload_tvb = tvb_new_subset(tvb, off, len, tvb_reported_length_remaining(tvb, offset) );
+		if ( ! dissector_try_heuristic(heur_epl_data_subdissector_list, payload_tvb, pinfo, epl_tree, NULL))
+			call_dissector(data_dissector, payload_tvb, pinfo, epl_tree);
+
+		off += len;
+	}
+
+	return off;
+}
+
+gint
 dissect_epl_soc(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, gint offset)
 {
 	nstime_t nettime;
@@ -949,16 +972,11 @@ dissect_epl_preq(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, gint o
 	len = tvb_get_letohs(tvb, offset);
 	proto_tree_add_uint(epl_tree, hf_epl_preq_size, tvb, offset, 2, len);
 
-	offset += 2;
-
-	if (len > 0)
-	{
-		proto_tree_add_item(epl_tree, hf_epl_preq_pl, tvb, offset, len, ENC_NA);
-	}
-	offset += len;
-
 	col_append_fstr(pinfo->cinfo, COL_INFO, "RD = %d   size = %d   ver = %d.%d",
-						(EPL_PDO_RD_MASK & flags), len, hi_nibble(pdoversion), lo_nibble(pdoversion));
+			(EPL_PDO_RD_MASK & flags), len, hi_nibble(pdoversion), lo_nibble(pdoversion));
+
+	offset += 2;
+	offset += dissect_epl_payload(epl_tree, tvb, pinfo, offset, len);
 
 	return offset;
 }
@@ -1000,21 +1018,16 @@ dissect_epl_pres(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, guint8
 	len = tvb_get_letohs(tvb, offset);
 	proto_tree_add_uint(epl_tree, hf_epl_pres_size, tvb, offset, 2, len);
 
-	offset += 2;
-	if (len > 0)
-	{
-		proto_tree_add_item(epl_tree, hf_epl_pres_pl, tvb, offset, len, ENC_NA);
-	}
-	offset += len;
-
 	col_append_fstr(pinfo->cinfo, COL_INFO, "RD = %d   size = %d   ver = %d.%d",
-						(EPL_PDO_RD_MASK & flags), len, hi_nibble(pdoversion), lo_nibble(pdoversion));
+			(EPL_PDO_RD_MASK & flags), len, hi_nibble(pdoversion), lo_nibble(pdoversion));
+
+	offset += 2;
+	offset += dissect_epl_payload ( epl_tree, tvb, pinfo, offset, len );
 
 	return offset;
 }
 
 
-
 gint
 dissect_epl_soa(proto_tree *epl_tree, tvbuff_t *tvb, packet_info *pinfo, guint8 epl_src, gint offset)
 {
@@ -1613,8 +1626,7 @@ dissect_epl_sdo_command_write_by_index(proto_tree *epl_tree, tvbuff_t *tvb, pack
 
 		size = tvb_reported_length_remaining(tvb, offset);
 
-		proto_tree_add_item(sdo_data_tree, hf_epl_asnd_sdo_cmd_data_data, tvb, offset, size, ENC_NA);
-		offset += size;
+		offset += dissect_epl_payload ( sdo_data_tree, tvb, pinfo, offset, size );
 	}
 	else
 	{
@@ -1696,7 +1708,7 @@ dissect_epl_sdo_command_write_multiple_by_index(proto_tree *epl_tree, tvbuff_t *
 			if ( size > 4 )
 				size = size - padding;
 
-			proto_tree_add_item(sdo_data_tree, hf_epl_asnd_sdo_cmd_data_data, tvb, dataoffset, size, ENC_NA);
+			dissect_epl_payload ( sdo_data_tree, tvb, pinfo, dataoffset, size );
 
 			offset += datalength;
 		}
@@ -1742,7 +1754,7 @@ dissect_epl_sdo_command_read_by_index(proto_tree *epl_tree, tvbuff_t *tvb, packe
 					val_to_str(segmented, epl_sdo_asnd_cmd_segmentation, "Unknown (%d)"));
 
 		size = tvb_reported_length_remaining(tvb, offset);
-		proto_tree_add_item(sdo_data_tree, hf_epl_asnd_sdo_cmd_data_data, tvb, offset, size, ENC_NA);
+		offset += dissect_epl_payload ( sdo_data_tree, tvb, pinfo, offset, size );
 
 		offset += size;
 	}
@@ -1815,10 +1827,6 @@ proto_register_epl(void)
 			{ "Size", "epl.preq.size",
 				FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL }
 		},
-		{ &hf_epl_preq_pl,
-			{ "Payload", "epl.preq.pl",
-				FT_BYTES, BASE_NONE, NULL, 0x00, NULL, HFILL }
-		},
 
 		/* PRes data fields*/
 		{ &hf_epl_pres_stat_ms,
@@ -1857,10 +1865,6 @@ proto_register_epl(void)
 			{ "Size", "epl.pres.size",
 				FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL }
 		},
-		{ &hf_epl_pres_pl,
-			{ "Payload", "epl.pres.pl",
-				FT_BYTES, BASE_NONE, NULL, 0x00, NULL, HFILL }
-		},
 
 		/* SoA data fields*/
 		{ &hf_epl_soa_stat_ms,
@@ -2309,10 +2313,6 @@ proto_register_epl(void)
 			{ "OD SubIndex", "epl.asnd.sdo.cmd.data.subindex",
 				FT_UINT8, BASE_HEX, NULL, 0x00, NULL, HFILL }
 		},
-		{ &hf_epl_asnd_sdo_cmd_data_data,
-			{ "Payload", "epl.asnd.sdo.cmd.data.data",
-				FT_BYTES, BASE_NONE, NULL, 0x00, NULL, HFILL }
-		},
 	};
 
 	/* Setup protocol subtree array */
@@ -2337,6 +2337,7 @@ proto_register_epl(void)
 
 	/* subdissector code */
 	register_heur_dissector_list("epl", &heur_epl_subdissector_list);
+	register_heur_dissector_list("epl_data", &heur_epl_data_subdissector_list);
 
 	/* Registering protocol to be called by another dissector */
 	epl_handle = new_register_dissector("epl", dissect_epl, proto_epl);