Allow to set engine_id (observationDomainId).

Thanks for #57 to bc-davidb@github.

Author: aabc

README

@@ -572,10 +572,21 @@ ipt_NETFLOW linux 2.6.x-4.x kernel module by <abc@telekom.ru> -- 2008-2016.
        desirable to combine it with packet processing on very highly loaded
        routers.
 
-       This option also could be changed at runtime with: 
+       This option could be changed at runtime with:
 
          # echo number > /sys/module/ipt_NETFLOW/parameters/exportcpu
 
+   engine_id=number
+     - Observation Domain ID (on IPFIX, Source Id on NetFlow v9, or Engine Id
+       on NetFlow v5) value to be exported. This may help your collector to
+       distinguish between multiple exporters. On Netflow v9 and IPFIX this
+       value is 32-bit on NetFlow v5 only 8 low bits are significant.
+       Default value is 0.
+
+       This option could be changed at runtime with:
+
+         # echo number > /sys/module/ipt_NETFLOW/parameters/engine_id
+
 
 ====================
 = HOW TO READ STAT =

ipt_NETFLOW.c

@@ -209,6 +209,10 @@ MODULE_PARM_DESC(maxflows, "maximum number of flows");
 static int peakflows = 0;
 static unsigned long peakflows_at; /* jfffies */
 
+static int engine_id = 0;
+module_param(engine_id, int, 0644);
+MODULE_PARM_DESC(engine_id, "Observation Domain ID");
+
 #ifdef ENABLE_AGGR
 #define AGGR_SIZE 1024
 static char aggregation_buf[AGGR_SIZE] = "";
@@ -271,7 +275,6 @@ static union {
 	struct netflow9_pdu v9;
 	struct ipfix_pdu ipfix;
 } pdu;
-static int engine_id = 0; /* Observation Domain */
 static __u8 *pdu_data_used;
 static __u8 *pdu_high_wm; /* high watermark */
 static struct flowset_data *pdu_flowset = NULL; /* current data flowset */
@@ -2532,7 +2535,7 @@ static void netflow_export_pdu_v5(void)
 	pdu.v5.ts_unsecs	= htonl(tv.tv_usec);
 	pdu.v5.seq		= htonl(pdu_seq);
 	//pdu.v5.eng_type	= 0;
-	pdu.v5.eng_id		= engine_id;
+	pdu.v5.eng_id		= (__u8)engine_id;
 #ifdef ENABLE_SAMPLER
 	pdu.v5.sampling		= htons(sampler_nf_v5());
 #endif