3.1.1. Makefile

Makefile. A good template is available from NET-SNMP Tutorial. I have modified the template to compile the generated C code.

OBJS2=example-demon.o netSnmpIETFWGTable.o
TARGETS=example-demon

CFLAGS=-I. `net-snmp-config --cflags`
BUILDLIBS=`net-snmp-config --libs`
BUILDAGENTLIBS=`net-snmp-config --agent-libs`

# shared library flags (assumes gcc)
DLFLAGS=-fPIC -shared

all: $(TARGETS)

example-demon: $(OBJS2)
        $(CC) -o example-demon $(OBJS2)  $(BUILDAGENTLIBS)
netSnmpIETFWGTable.o: netSnmpIETFWGTable.c Makefile
        $(CC) $(CFLAGS) $(DLFLAGS) -c -o netSnmpIETFWGTable.o \
                netSnmpIETFWGTable.c
        $(CC) $(CFLAGS) $(DLFLAGS) -o netSnmpIETFWGTable.so \
                netSnmpIETFWGTable.o
              

3.1.2. Sub-agent daemon code

The daemon will use the generated sub-agent code. This example daemon code has been taken from NET-SNMP Tutorial

#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>

#include <signal.h>

#include <netSnmpIETFWGTable.h>
        
static int keep_running;

RETSIGTYPE
stop_server(int a) {
    keep_running = 0;
}

int
main (int argc, char **argv) {
  int agentx_subagent=1; /* change this if you want to 
        be a SNMP master agent */

  /* print log errors to stderr */
  snmp_enable_stderrlog();
  //snmp_set_do_debugging(1);
  /* we're an agentx subagent? */
  if (agentx_subagent) {
    /* make us a agentx client. */
    netsnmp_ds_set_boolean(NETSNMP_DS_APPLICATION_ID, 
                NETSNMP_DS_AGENT_ROLE, 1);
  }

        DEBUGMSG(("Before agent library init","\n"));
  /* initialize the agent library */
  init_agent("example-demon");

  /* initialize mib code here */

  /* mib code: nit_netSnmpIETFWGTable from init_netSnmpIETFWGTable.c */
        init_netSnmpIETFWGTable();

  /* example-demon will be used to read example-demon.conf files. */
  init_snmp("example-demon");

  /* If we're going to be a snmp master agent, initial the ports */
  if (!agentx_subagent)
    init_master_agent();  /* open the port to listen on 
        (defaults to udp:161) */

  /* In case we recevie a request to stop (kill -TERM or kill -INT) */
  keep_running = 1;
  signal(SIGTERM, stop_server);
  signal(SIGINT, stop_server);

  /* you're main loop here... */
  while(keep_running) {
    /* if you use select(), see snmp_select_info() in snmp_api(3) */
    /*     --- OR ---  */
    agent_check_and_process(1); /* 0 == don't block */
  }

  /* at shutdown time */
  snmp_shutdown("example-demon");
        return 1;
}
              

The only change from the original source file code was replacing init_nstAgentSubagentObject(); with init_netSnmpIETFWGTable();.

For right now we will skip explanation of these two files and concentrate on the sub-agent generated code.