Added pf_ring load balancing support to the scripting layer.

- If the misc/pf-ring-load-balancing script is loaded, the correct
  environment variables will be set to enable automatic flow based
  load balancing used pf_ring if Bro is built against the pf_ring
  libpcap wrapper.  Loading the script on non-Linux OSs or when Bro
  isn't linked against the correct libpcap has no known side effects
  since the script just sets environment variables.

- Added a BiF named setenv for setting environment variables.

scripts/policy/misc/pf-ring-load-balancing.bro

@@ -0,0 +1,22 @@
+##! This script adds the necessary environment variables for Bro to make use 
+##! of PF_RING's clustering (and load balancing) support through the libpcap
+##! wrapper.
+
+module PF_Ring;
+
+export {
+	## Define the pf_ring cluster ID that you would like this instance
+	## of Bro to use.  Please set a value from 0 to 255
+	const cluster_id = 150 &redef;
+}
+
+
+event bro_init() &priority=10
+	{
+	if ( cluster_id > 255 || cluster_id < 0 )
+		Reporter::fatal(fmt("%d is an invalid value for PF_Ring::cluster_id", cluster_id));
+	
+	if ( ! setenv("PCAP_PF_RING_USE_CLUSTER_PER_FLOW", "1") ||
+	     ! setenv("PCAP_PF_RING_CLUSTER_ID", fmt("%d", cluster_id)) )
+		Reporter::fatal("Unable to set the PF_RING environment variable.");
+	}

src/bro.bif

@@ -791,6 +791,16 @@ function getenv%(var: string%): string
 	return new StringVal(env_val);
 	%}
 
+function setenv%(var: string, val: string%): bool
+	%{
+	int result = setenv(var->AsString()->CheckString(), 
+	                    val->AsString()->CheckString(), 1);
+	
+	if ( result < 0 )
+		return new Val(0, TYPE_BOOL);
+	return new Val(1, TYPE_BOOL);
+	%}
+
 function sqrt%(x: double%): double
 	%{
 	if ( x < 0 )