TUT:mib2c_scalar

The mib2c scalar configuration file generates a bare-bones skeleton handler for each scalar object. You must then write code to provide data for the object, handling each mode. For a complete example, see the IP-MIB scalars implementation in the source tree. Here is an excerpt:

int ipAddressSpinLockValue;

int
handle_ipAddressSpinLock(netsnmp_mib_handler *handler,
                         netsnmp_handler_registration *reginfo,
                         netsnmp_agent_request_info *reqinfo,
                         netsnmp_request_info *requests);

/** Initializes the ip module */
void init_ip_scalars(void)
{
    static oid      ipAddressSpinLock_oid[] = { 1, 3, 6, 1, 2, 1, 4, 33 };

    DEBUGMSGTL(("ip_scalar", "Initializing\n"));

    netsnmp_register_scalar(netsnmp_create_handler_registration
                            ("ipAddressSpinLock", handle_ipAddressSpinLock,
                             ipAddressSpinLock_oid,
                             OID_LENGTH(ipAddressSpinLock_oid),
                             HANDLER_CAN_RWRITE));

    /* Initialize spin lock with random value */
    ipAddressSpinLockValue = (int) random();

}

int
handle_ipAddressSpinLock(netsnmp_mib_handler *handler,
                          netsnmp_handler_registration *reginfo,
                          netsnmp_agent_request_info   *reqinfo,
                          netsnmp_request_info         *requests)
{
    long   value;

    /* We are never called for a GETNEXT if it's registered as a
       "instance", as it's "magically" handled for us.  */

    /* a instance handler also only hands us one request at a time, so
       we don't need to loop over a list of requests; we'll only get one. */

    switch(reqinfo->mode) {

        case MODE_GET:
            snmp_set_var_typed_value(requests->requestvb, ASN_INTEGER,
                                     (u_char *)&ipAddressSpinLockValue,
                                     sizeof(ipAddressSpinLockValue));
            break;

#ifndef NETSNMP_NO_WRITE_SUPPORT
        /*
         * SET REQUEST
         *
         * multiple states in the transaction.  See:
         * http://www.net-snmp.org/tutorial-5/toolkit/mib_module/set-actions.jpg
         */
        case MODE_SET_RESERVE1:
        case MODE_SET_RESERVE2:
            /* just check the value */
            value =  *(requests->requestvb->val.integer);
            if (value != ipAddressSpinLockValue)
                netsnmp_set_request_error(reqinfo, requests, SNMP_ERR_INCONSISTENTVALUE);
            break;

        case MODE_SET_FREE:
            break;

        case MODE_SET_ACTION:
            /* perform the final spinlock check and increase its value */
            value =  *(requests->requestvb->val.integer);
            if (value != ipAddressSpinLockValue) {
                netsnmp_set_request_error(reqinfo, requests, SNMP_ERR_INCONSISTENTVALUE);
            } else {
                ipAddressSpinLockValue++;
                /* and check it for overflow */
                if (ipAddressSpinLockValue > 2147483647 || ipAddressSpinLockValue < 0)
                    ipAddressSpinLockValue = 0;
            }
            break;

        case MODE_SET_COMMIT:
            break;

        case MODE_SET_UNDO:
             break;
#endif /* !NETSNMP_NO_WRITE_SUPPORT */

        default:
            /* we should never get here, so this is a really bad error */
            snmp_log(LOG_ERR, "unknown mode (%d) in handle_ipAddressSpinLock\n", reqinfo->mode );
            return SNMP_ERR_GENERR;
    }

    return SNMP_ERR_NOERROR;
}