[ECOS] How to make lwip SNMP work

[Michael Jones <mjones at linear dot com>]

It took some effort to figure out how to make SNMP work with LWIP and private MIB. I left a little code in bug 1001789, but here is working code that does not have memory leaks and seems to work consistently. I don't know for sure if the callback is required, but it does ensure the trap runs on the tcpip thread, and from what I have read, this needs to be the case.

This works on kinetis K60 with the lwip sequential interface enbled.

#ifndef SNMP_H_
#define SNMP_H_

#include "lwip/snmp_structs.h"
#include "lwip/tcpip.h"
#include <stdint.h>
#include "pmbus.h"

#define SNMP_SEND_TRAP 		1

typedef struct snmp_message
{
   uint32_t                 COMMAND;
   struct ip_addr			ADDRESS;
   unsigned char			TRAP;
   char 					*message;
} SNMP_MESSAGE, *SNMP_MESSAGE_PTR;

extern void snmp_thread_entry(void *arg);

extern void send_trap(struct ip_addr addr, unsigned char trap, char *message);

#endif /* SNMP_H_ */


#include "private_mib.h"
#include "lwip/snmp.h"
#include "lwip/snmp_msg.h"
#include "lwip/snmp_asn1.h"
#include "lwip/snmp_structs.h"
#include "lwip/mem.h"
#include "snmp.h"

extern struct snmp_msg_trap trap_msg;

// Private MIB code from python script here

void
lwip_privmib_init(void)
{

}

void send_trap_callback( void * parameters )
{
		struct snmp_obj_id eoid;
		// There should be a way to do this directly.
		eoid.id[0] = enterprises_ids[1];
		eoid.len = 1;

		snmp_send_trap(SNMP_GENTRAP_ENTERPRISESPC, &eoid, 1);
		snmp_varbind_list_free(&trap_msg.outvb);
}

void snmp_thread_entry(void *arg)
{
	SNMP_MESSAGE_PTR snmp_message;
	struct snmp_obj_id objid;

	// There should be a better way to initialize this.
	objid.len = 1;
	objid.id[0] = private_ids[0];

	snmp_init();


	cyg_mbox_create(&snmp_mailbox_handle, &snmp_mailbox);

	while (1)
	{
		snmp_message = (SNMP_MESSAGE_PTR) cyg_mbox_get(snmp_mailbox_handle);
		if (snmp_message->COMMAND == SNMP_SEND_TRAP)
		{
			struct ip_addr addr;
			// Reverse the bytes because snmp_trap_dst_ip_set reverses them again.
			addr.addr = htonl(snmp_message->ADDRESS.addr);
			snmp_trap_dst_ip_set(0,&addr);
			snmp_trap_dst_enable(0,snmp_message->TRAP);

			struct snmp_varbind *vb = snmp_varbind_alloc(&objid, SNMP_ASN1_OPAQUE, strlen(snmp_message->message)+1);
			if (vb == NULL)
			{
				diag_printf("SNMP failure to allocate memory\n");
				continue;
			}
			strcpy (vb->value, snmp_message->message);
			snmp_varbind_tail_add(&trap_msg.outvb,vb);
			tcpip_callback(send_trap_callback, NULL);
		}
		free(snmp_message->message);
		free(snmp_message);
	}
}

void send_trap(struct ip_addr addr, unsigned char trap, char *message)
{
	SNMP_MESSAGE_PTR snmp_message = (SNMP_MESSAGE_PTR) malloc(sizeof(SNMP_MESSAGE));
	snmp_message->COMMAND = SNMP_SEND_TRAP;
	snmp_message->TRAP = trap;
	snmp_message->ADDRESS = addr;
	snmp_message->message = (char*) malloc(strlen(message)+1);
	strcpy(snmp_message->message, message);
	cyg_mbox_put(snmp_mailbox_handle, (void *) snmp_message);
}


Code to start the snmp thread:

void start_network(cyg_addrword_t p)
{
	struct ip_addr ipaddr, netmask, gw;
	struct netif *netif;

	/* Set network address variables */
	IP_GATEWAY(&gw);
	IP_ADDRESS(&ipaddr);
	IP_MASK(&netmask);

	//tcpip_init(NULL, NULL);

	// Check return for null
	//netif_result = netif_add(&netif, &ipaddr, &netmask, &gw, NULL, init_ip, tcpip_input);
	//netif_set_up(&netif);

    cyg_lwip_sequential_init();

    netif = netif_find("et0");
    netif_set_ipaddr(netif, &ipaddr);
    netif_set_netmask(netif, &netmask);
    netif_set_gw(netif, &gw);

    netif_set_up(netif);

    cyg_lwip_thread_new("snmp", snmp_thread_entry, NULL,
                        snmp_stack, STACK_SIZE, 7);

    cyg_thread_exit();
}


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