Help needed in making an AgentX subagent work...

Hello everyone,

Sorry to bother you with something that many will certainly find 
trivial, but it's been driving me crazy for days, now... Even though I 
read all tutorials I found, I'm pretty sure I'm missing a little 
something that prevents my program from working... Maybe I misunderstood 
something (English is not my mother tongue), or I thought something does 
not apply in my case whereas it does... Anyhow - I'm really lost and in 
need for enlighted advise.

I'm writing a sub-agent, and all I want to do, is to have my handler 
called back whenever a request (be it GET or SET) is made on an OID 
under a given root one. Computation of the values to return will be a 
bit messy, so I don't want to use all the pretty functionalities that 
net-snmp provides, such as 'netsnmp_register_long_scalar' functions and 
the like. Just a callback, and I'll take care of the answering.

I'm coding in C on a Fedora 25 box, with NET-SNMP version 5.7.3, on an 
isolated network - so security is not an issue (I'll be using SNMP v1 or 
v2c, with all rights given to public community).

Here is what my snmpd.conf looks like (comments removed) :
-----------------------------------------------------------
master agentx
com2sec  supervision    default       public
group   DefaultGroup   v1            supervision
group   DefaultGroup   v2c           supervision
view    systemview    included   .1
view    systemview    included   .1.3.6.1.2.1.1
view    systemview    included   .1.3.6.1.2.1.25.1.1
view    myapplview    included   .1.3.6.1.4.1.XXXX.YYYY
access   DefaultGroup   ""      any       noauth exact  systemview 
systemview systemview
access   DefaultGroup   ""      any       noauth exact  myapplview 
myapplview myapplview
syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root <root@localhost> (configure /etc/snmp/snmp.local.conf)
-----------------------------------------------------------

... and I can check, using journalctl, that the AgentX support has been 
enabled by the snmpd daemon :
 > snmpd[749]: Turning on AgentX master support.

When I try to get a "standard" OID, it works fine :
 > $ snmpget -v 2c -c public localhost DISMAN-EVENT-MIB::sysUpTimeInstance
 > DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (2530359) 7:01:43.59

... but when I try to get one of mine, it can't be found :
 > $ snmpget -v 2c -c public localhost .1.3.6.1.4.1.XXXX.YYYY
 > SNMPv2-SMI::enterprises.XXXX.YYYY = No Such Object available on this 
agent at this OID

Here is what my code looks like (once more, it's a simplified version ; 
on the real code, *all* errors are handled... and none happen) :
-----------------------------------------------------------
oid root_oid[] = {1,3,6,1,4,1,XXXX,YYYY};

int my_handler(netsnmp_mib_handler          *mh,
                netsnmp_handler_registration *hr,
                netsnmp_agent_request_info   *ari,
                netsnmp_request_info         *ri) {
   puts("Handler has been called :-) !");
   return SNMP_ERR_NOERROR;
}

int main(void) {
   netsnmp_handler_registration *hr;
   bool dont_stop = true; // modified elsewhere when I want to quit

   snmp_enable_stderrlog();
   init_agent("MyAgent");
   netsnmp_ds_set_boolean(NETSNMP_DS_APPLICATION_ID, 
NETSNMP_DS_AGENT_ROLE, 1);
   hr = netsnmp_create_handler_registration("MyAgent",
                                            my_handler,
                                            root_oid,
                                            root_oid_len,// initialized 
elsewhere
HANDLER_CAN_RWRITE);
   netsnmp_register_handler(hr);
   init_snmp("MyAgent");
   while (dont_stop) agent_check_and_process(1);
   snmp_shutdown("MyAgent");
   return 0;
}
-----------------------------------------------------------
I simply compile with :
 > gcc -O2 -I inc -Wall -Wextra -Werror src/myappl.c -lpthread -lnetsnmp 
-lnetsnmpagent -o bin/myappl

myappl runs fine up to the "while (dont_stop)" loop, and correctly stops 
whenever Ctrl-C is pressed (which makes dont_stop false).
In the meanwhile, I do the snmpget command above. Of course, I never see 
the "handler has been called" message...

So... does anyone out there have a clue about what I am doing wrong ?
... or just a pointer on what to check ?

I'm really lost there, so any help would be appreciated...



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