Re: Unexpected behaviour

There is not much activity on this mailing list (or is it just me being impatient waiting for some response). Is there a forum for net-snmp where I could query my problems? 

I am completely baffled about this behavior, tried several remedies, but unable to fix it. I need to avoid calling my device multiple times, since both handler and callback are executed multiple times. 

My technique of putting each request(delegated_cache) in a list did not work so well. Beside it will not work if I get two requests for the same OID. 

----- Original Message ----- 

Fra: "Sverre Moe" <[email protected]> 
Til: [email protected] 
Sendt: 5. november 2012 14:11:56 
Emne: Unexpected behaviour 

I have implemented a delegated response with a 2 seconds delay time. 

My handler function handle_snmp and callback function delayed_response gets called/executed several times for the same requests. Why is that? Is it a feature or a bug? If its a feature is it how it handles the delay by executing it multiple times within the delay time? 

In order to avoid querying the device multiple times per request I have implemented a list of active requests. This list holds a pointer to a netsnmp_delegated_cache. When I have gotten the response/value from the device I then remove the request from the active request list. However when this value is retrieved handle_snmp and delayed_response are not yet finished and may be executed a few times more before it ends. Thus it may query the device again. 

Can I terminate the delay earlier than the defined delay if I have gotten the value I need? 

int 
handle_snmp(netsnmp_mib_handler *handler, 
netsnmp_handler_registration *reginfo, 
netsnmp_agent_request_info *reqinfo, 
netsnmp_request_info *requests) { 

const oid* request_oid = (*reginfo).rootoid; 
const size_t request_oid_length = (*reginfo).rootoid_len - 1; //removes the trailing .0 

bool request_active = false; 
list<netsnmp_delegated_cache*>::iterator request_iterator; 
for (request_iterator = active_requests.begin(); 
request_iterator != active_requests.end(); 
request_iterator++) { 
netsnmp_delegated_cache *delegated_cache = (*request_iterator); 
netsnmp_handler_registration *delegated_reginfo = delegated_cache->reginfo; 
const oid* oid_value = (*delegated_reginfo).rootoid; 
const size_t oid_length = (*delegated_reginfo).rootoid_len - 1; //removes the trailing .0 
if (netsnmp_oid_equals(oid_value, oid_length, request_oid, request_oid_length) == 0) { 
request_active = true; 
break; 
} 
} 

netsnmp_delegated_cache *cache = 
netsnmp_create_delegated_cache(handler, reginfo, reqinfo, requests, NULL); 

map<oid_wrapper, scalar>::iterator scalar_iterator; 
for (scalar_iterator = scalars.begin(); 
scalar_iterator != scalars.end(); 
scalar_iterator++) { 
const oid_wrapper oid_wrapper = (*scalar_iterator).first; 
const oid* oid_value = oid_wrapper.get_oid(); 
const int oid_length = oid_wrapper.get_length(); 
if (netsnmp_oid_equals(oid_value, oid_length, request_oid, request_oid_length) == 0) { 
if (!request_active) { //request is active, no need to query middleware again. 
active_requests.push_back(cache); 

scalar _scalar = (*scalar_iterator).second; 
const string scalar_path = _scalar.getPath(); 
const string scalar_type = _scalar.getType(); 
//My own call to retrieve value from device... 
} 
break; 
} 
} 

/* 
* mark this variable as something that can't be handled now. 
* We'll answer it later. 
*/ 
requests->delegated = 1; 

snmp_alarm_register(delay_time, /* delay */ 
0, /* repeat */ 
delayed_response, /* the function to call */ 
(void *) cache); 

return SNMP_ERR_NOERROR; 
} 

void 
delayed_response(unsigned int clientreg, void *clientarg) { 
/* 
* extract the cache from the passed argument 
*/ 
netsnmp_delegated_cache *cache = (netsnmp_delegated_cache *) clientarg; 

netsnmp_request_info *requests; 
netsnmp_agent_request_info *reqinfo; 
netsnmp_handler_registration *reginfo; 

/* 
* here we double check that the cache we created earlier is still 
* valid. If not, the request timed out for some reason and we 
* don't need to keep processing things. Should never happen, but 
* this double checks. 
*/ 
cache = netsnmp_handler_check_cache(cache); 

if (!cache) { 
snmp_log(LOG_ERR, "illegal call to return delayed response\n"); 
return; 
} 

//re-establish the previous pointers we are used to having 
reqinfo = cache->reqinfo; 
reginfo = cache->reginfo; 
requests = cache->requests; 
const oid* request_oid = (*reginfo).rootoid; 
const size_t request_oid_length = (*reginfo).rootoid_len; 

void* datapointer; 
char buffer[2048]; 
int dataint; 
int length = 0; 
u_char type; 

bool found = false; 
map<oid_wrapper, status>::iterator status_iterator; 
for (status_iterator = available_status.begin(); 
status_iterator != available_status.end(); 
status_iterator++) { 
const oid_wrapper oid_wrapper = (*status_iterator).first; 
const oid* oid_value = oid_wrapper.get_oid(); 
const int oid_length = oid_wrapper.get_length(); 
if (netsnmp_oid_equals(oid_value, oid_length, request_oid, request_oid_length) == 0) { 
const status _status = (*status_iterator).second; 
const string value = _status.getValue(); 
found = true; 

strcpy(buffer, value.c_str()); 
datapointer = buffer; 
length = strlen(buffer); 
type = ASN_OCTET_STR; 

//Value retrieved. We now remove it. 
available_status.erase(status_iterator); 
break; 
} 
} 

/* 
* mention that it's no longer delegated, 
* and we've now answered the query. 
*/ 
requests->delegated = 0; 

if (found) { 
list<netsnmp_delegated_cache*>::iterator request_iterator; 
for (request_iterator = active_requests.begin(); 
request_iterator != active_requests.end(); 
request_iterator++) { 
netsnmp_delegated_cache *delegated_cache = (*request_iterator); 
netsnmp_handler_registration *delegated_reginfo = delegated_cache->reginfo; 
const oid* oid_value = (*delegated_reginfo).rootoid; 
const size_t oid_length = (*delegated_reginfo).rootoid_len; 
if (netsnmp_oid_equals(oid_value, oid_length, request_oid, request_oid_length) == 0) { 
active_requests.erase(request_iterator); 
break; 
} 
} 

snmp_set_var_typed_value(cache->requests->requestvb, 
type, 
datapointer, 
length); 
} else { 
netsnmp_set_request_error(reqinfo, requests, SNMP_ERR_GENERR); 
} 

//free the information cache 
netsnmp_free_delegated_cache(cache); 
} 

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