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/** @example delayed_instance.c
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* This example implements the netSnmpExampleSleeper object.
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* It demonstrates 2 things:
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* - The instance helper, which is a way of registering an exact OID
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* such that GENEXT requests are handled entirely by the helper.
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* - how to implement objects which normally would block the agent as
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* it waits for external events in such a way that the agent can
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* continue responding to other requests while this implementation
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* - Added bonus: normally the nsTransactionTable is empty, since
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* there aren't any outstanding requests generally. When accessed,
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* this module will create some however. Try setting
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* netSnmpExampleSleeper.0 to 10 and then accessing it (use
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* "snmpget -t 15 ..." to access it), and then walk the
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* nsTransactionTable from another shell to see that not only is
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* the walk not blocked, but that the nsTransactionTable is not
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#include <net-snmp/net-snmp-config.h>
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#include <net-snmp/net-snmp-includes.h>
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#include <net-snmp/agent/net-snmp-agent-includes.h>
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#include "delayed_instance.h"
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static u_long delay_time = 1;
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init_delayed_instance(void)
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static oid my_delayed_oid[] =
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{ 1, 3, 6, 1, 4, 1, 8072, 2, 1, 2, 0 };
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* delayed handler test
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netsnmp_handler_registration *my_test;
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netsnmp_create_handler_registration("delayed_instance_example",
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delayed_instance_handler,
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OID_LENGTH(my_delayed_oid),
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netsnmp_register_instance(my_test);
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#define DELAYED_INSTANCE_SET_NAME "test_delayed"
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delayed_instance_handler(netsnmp_mib_handler *handler,
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netsnmp_handler_registration *reginfo,
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netsnmp_agent_request_info *reqinfo,
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netsnmp_request_info *requests)
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DEBUGMSGTL(("delayed_instance", "Got request, mode = %d:\n",
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switch (reqinfo->mode) {
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* here we merely mention that we'll answer this request
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* later. we don't actually care about the mode type in this
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* example, but for certain cases you may, so I'll leave in the
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* otherwise useless switch and case statements
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* mark this variable as something that can't be handled now.
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* We'll answer it later.
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requests->delegated = 1;
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* register an alarm to update the results at a later
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* time. Normally, we might have to query something else
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* (like an external request sent to a different network
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* or system socket, etc), but for this example we'll do
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* something really simply and just insert an alarm for a
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* certain period of time
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snmp_alarm_register(delay_time, /* seconds */
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return_delayed_response, /* the function
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* here we create a "cache" of useful
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* information that we'll want later
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* on. This argument is passed back
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* to us in the callback function for
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netsnmp_create_delegated_cache(handler,
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return SNMP_ERR_NOERROR;
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return_delayed_response(unsigned int clientreg, void *clientarg)
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* extract the cache from the passed argument
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netsnmp_delegated_cache *cache = (netsnmp_delegated_cache *) clientarg;
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netsnmp_request_info *requests;
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netsnmp_agent_request_info *reqinfo;
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u_long *delay_time_cache = NULL;
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* here we double check that the cache we created earlier is still
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* * valid. If not, the request timed out for some reason and we
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* * don't need to keep processing things. Should never happen, but
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* * this double checks.
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cache = netsnmp_handler_check_cache(cache);
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snmp_log(LOG_ERR, "illegal call to return delayed response\n");
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* re-establish the previous pointers we are used to having
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reqinfo = cache->reqinfo;
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requests = cache->requests;
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DEBUGMSGTL(("delayed_instance",
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"continuing delayed request, mode = %d\n",
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cache->reqinfo->mode));
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* mention that it's no longer delegated, and we've now answered
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* the query (which we'll do down below).
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requests->delegated = 0;
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switch (cache->reqinfo->mode) {
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* registering as an instance means we don't need to deal with
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* getnext processing, so we don't handle it here at all.
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* However, since the instance handler already reset the mode
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* back to GETNEXT from the faked GET mode, we need to do the
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* same thing in both cases. This should be fixed in future
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* versions of net-snmp hopefully.
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* return the currend delay time
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snmp_set_var_typed_value(cache->requests->requestvb,
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(u_char *) & delay_time,
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case MODE_SET_RESERVE1:
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if (requests->requestvb->type != ASN_INTEGER) {
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* not an integer. Bad dog, no bone.
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netsnmp_set_request_error(reqinfo, requests,
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* we don't need the cache any longer
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netsnmp_free_delegated_cache(cache);
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case MODE_SET_RESERVE2:
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* store old value for UNDO support in the future.
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memdup((u_char **) & delay_time_cache,
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(u_char *) & delay_time, sizeof(delay_time));
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if (delay_time_cache == NULL) {
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netsnmp_set_request_error(reqinfo, requests,
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SNMP_ERR_RESOURCEUNAVAILABLE);
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netsnmp_free_delegated_cache(cache);
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* Add our temporary information to the request itself.
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* This is then retrivable later. The free function
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* passed auto-frees it when the request is later
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netsnmp_request_add_list_data(requests,
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netsnmp_create_data_list
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(DELAYED_INSTANCE_SET_NAME,
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delay_time_cache, free));
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case MODE_SET_ACTION:
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* update current value
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delay_time = *(requests->requestvb->val.integer);
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DEBUGMSGTL(("testhandler", "updated delay_time -> %d\n",
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* ack, something somewhere failed. We reset back to the
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* previously old value by extracting the previosuly
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* stored information back out of the request
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*((u_long *) netsnmp_request_get_list_data(requests,
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DELAYED_INSTANCE_SET_NAME));
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case MODE_SET_COMMIT:
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* the only thing to do here is free the old memdup'ed
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* value, but it's auto-freed by the datalist recovery, so
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* we don't have anything to actually do here
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* free the information cache
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netsnmp_free_delegated_cache(cache);
added
removed
agent/mibgroup/examples/delayed_instance.c
