Re: Problems registering AgentX (in C)

On Wed, Aug 12, 2015 at 6:47 AM, Ulrich Windl <
[email protected]> wrote:

> Hi again!
>
> Even after adding "snmp_set_do_debugging(1);" at the beginning of my
> program, I have no real clue; the last lines I get are these:
> ---
> trace: snmp_sess_select_info(): snmp_api.c, 5862:
> sess_select: for all sessions: 5 3
> sess_select: next alarm 0.-1020349360 sec
> sess_select: blocking:no session requests or alarms.
> ---
>
> I'm wondering: How does main() automatically process the options in the
> tutorial ("% ./mysubagent -f -Lo -x  tcp:localhost:1705")? The
> example-daemon.c has no special commands for that.
>

I built my main around the one that "net-snmp-config --compile-subagent"
creates for you.  It has lots of useful command-line parsing, including
config files, debugging, forking, etc. You can add the "--norm" argument to
"net-snmp-config --compile-subagent" and it will say "leaving the temporary
code file: arglebargle.c" and then you can rename it and build it yourself.

>
> I found one problem: I missed to add 'init_snmp("testagent");', but even
> then it didn't work.
>
> Found the most important problem: Once I put the local config file
> (testagent.conf) into /etc/snmp, the agent became much more alive!
>
> So the final question is: Is there a way to tell your subagent to locate
> the config file in the current directory? If you need to put it into
> /etc/snmp, you need root rights for development, and having a local,
> non-priviledged snmp Daemon for testing makes no sense.
>

If you use the command line parsing suggested above, you can run it with
"-c whatever.conf".  If you don't want to do that, you can specify the
config file inside your main() with
netsnmp_ds_set_string(NETSNMP_DS_LIBRARY_ID,NETSNMP_DS_LIB_OPTIONALCONFIG,
"whatever.conf");

  Bill


> Regards,
> Ulrich
>
> >>> "Ulrich Windl" <[email protected]> schrieb am
> 12.08.2015 um
> 12:01 in Nachricht <[email protected]>:
> > Hi!
> >
> > I got absolute zero replies to my message, so I created an isolated test
> > case in the mean-time. The test case looks like this:
> >
> > static  volatile int    stop_requests = 0;      /* count stop requests */
> >
> > /* main */
> > int     main(int argc, char *argv[])
> > {
> >         int             result  = 0;
> >
> >         /*BEGIN SNMP*/
> >         /* prepare for AgentX subagent */
> >         if ( netsnmp_ds_set_boolean(NETSNMP_DS_APPLICATION_ID,
> >                                     NETSNMP_DS_AGENT_ROLE, 1)
> >              != SNMPERR_SUCCESS )
> >         {
> >                 result = 2;
> >         }
> >         SOCK_STARTUP;           /* initialize TCP/IP, if necessary */
> >         init_agent("testagent");        /* initialize the agent library
> */
> >         init_IOTWatchMIB();     /* initialize MIB module */
> >         while ( stop_requests == 0 ) {
> >                 agent_check_and_process(1); /* 0 == don't block */
> >         }
> >
> >         /* at shutdown time */
> >         snmp_shutdown("testagent");
> >         SOCK_CLEANUP;
> >         /*END SNMP*/
> > quit:   return(result);
> > }
> >
> > When running the testagent with ltrace, I see the handlers are
> registered,
> > and the test agent waits for data:
> >
> > ---
> > SNMP> ltrace ./testagent
> > __libc_start_main(0x400f40, 1, 0x7ffc0e2bb4e8, 0x4011b0, 0x4011a0
> <unfinished
> > ...>
> > netsnmp_ds_set_boolean(1, 1, 1, 0, 0x7fd165f0f320) = 0
> > init_agent(0x4012a4, 0x7fd1663d1f40, 0, 1, 0x7fd165f0f320) = 0
> > snmp_get_do_debugging(1, 1, 0, 1, 0x2965736c61667c) = 0
> > netsnmp_create_handler_registration(0x40134d, 0x401040, 0x602120, 13, 1)
> =
> > 0x6071a0
> > netsnmp_register_scalar(0x6071a0, 0x602188, 0, 1, 1000) = 0
> > netsnmp_create_handler_registration(0x40135f, 0x400fd0, 0x6020a0, 13, 1)
> =
> > 0x607d40
> > netsnmp_register_scalar(0x607d40, 0x602108, 0, 2, 1000) = 0
> > agent_check_and_process(1, 0x7fd166a33049, 0, 0, 0x608050
> > ---
> >
> > However If I query the OIDs registered, no data are returned ("There is
> no
> > such variable name in this MIB.")
> >
> > The init Module looks like this:
> >
> > /** Initializes the IOTWatchMIB module */
> > void
> > init_IOTWatchMIB(void)
> > {
> >     static oid      giveItABetterName_oid[] =
> >         { 1, 3, 6, 1, 4, 1, 8072, 9999, 9999, 1000, 1, 1, 1 };
> >     static oid      giveThisANameToo_oid[] =
> >         { 1, 3, 6, 1, 4, 1, 8072, 9999, 9999, 1000, 1, 1, 2 };
> >
> >     DEBUGMSGTL(("IOTWatchMIB", "Initializing\n"));
> >
> >     netsnmp_register_scalar(netsnmp_create_handler_registration
> >                             ("giveItABetterName",
> handle_giveItABetterName,
> >                              giveItABetterName_oid,
> >                              OID_LENGTH(giveItABetterName_oid),
> >                              HANDLER_CAN_RONLY));
> >     netsnmp_register_scalar(netsnmp_create_handler_registration
> >                             ("giveThisANameToo", handle_giveThisANameToo,
> >                              giveThisANameToo_oid,
> >                              OID_LENGTH(giveThisANameToo_oid),
> >                              HANDLER_CAN_RONLY));
> > }
> >
> > (The handlers both should cause an abort if called (to help debugging)):
> >
> >     switch (reqinfo->mode) {
> >
> >     case MODE_GET:
> >         snmp_set_var_typed_value(requests->requestvb, ASN_INTEGER,
> >                                  (u_char *) 0 /* XXX: a pointer to the
> > scalar's data */
> >                                  , 1 /* XXX: the length of the data in
> bytes
> > */ );
> >         break;
> >
> > I have absolutely no idea how to debug this. While debugging I'm running
> > snmpd in user mode as suggested in the tutorial:
> > /usr/sbin/snmpd -f -Lo -C --rwcommunity=public --master=agentx \
> > --agentXSocket=tcp:localhost:1705 udp:1161 -Dagentx
> >
> > I fail to see where my testagent connects to the SNMP socket, nor do I
> see
> > that my config file is opened. The select() is on a pipe, but I cannot
> see
> > any other process in strace:
> > ---
> > 2819  munmap(0x7f84066bd000, 4096)      = 0
> > 2819  gettimeofday({1439373523, 620867}, NULL) = 0
> > 2819  pipe([3, 4])                      = 0
> > 2819  gettimeofday({1439373523, 621388}, NULL) = 0
> > 2819  pipe([5, 6])                      = 0
> > 2819  select(6, [3 5], NULL, NULL, NULL) = ? ERESTARTNOHAND (To be
> > restarted)
> > 2819  --- SIGINT (Interrupt) @ 0 (0) ---
> > 2819  +++ killed by SIGINT +++
> > ---
> >
> > Any ideas?
> >
> > Regards,
> > Ulrich
> >
> >>>> Ulrich Windl schrieb am 05.08.2015 um 10:42 in Nachricht
> <55C1CC7D.CAD : 161
> > :
> > 60728>:
> >> Hello!
> >>
> >> I had reported problems with registering an AgentX subagent in Perl (no
> >> error, but doesn't work). Finally I found the bug that prevented it from
> >> working.
> >>
> >> Now I have a C program that uses multiple threads to retrieve and
> monitor
> >> some values. I tried to make this program an AgentX subagent by adding
> the
> >> code from the C coding example. Unfortunately the same things as in Perl
> >> happen: The agent does not connect, and there is no error. When trying
> to
> >> access any of the registered OIDs, an error is returned. None of the
> > handlers
> >> is ever called.
> >>
> >> What I'd like to have eventually is that one thread takes care of all
> the
> >> SNMP handling.
> >>
> >> From the example I guess that the API is too high-level (init_agent()):
> It's
> >> hard to see which steps are actually executed, and what the results of
> these
> >
> >> steps are.
> >>
> >> What could the problem be, and how could I debug it?
> >>
> >> The essential code fragemnt looks like this:
> >>                 /*BEGIN SNMP*/
> >>                 /* prepare for AgentX subagent */
> >>                 if ( netsnmp_ds_set_boolean(NETSNMP_DS_APPLICATION_ID,
> >>                                             NETSNMP_DS_AGENT_ROLE, 1)
> >>                      != SNMPERR_SUCCESS )
> >>                 {
> >>                         /* report problem */
> >>                 }
> >>                 SOCK_STARTUP;           /* initialize TCP/IP, if
> necessary
> >> */
> >>                 init_agent("iotwatch"); /* initialize the agent library
> */
> >>                 init_IOTWatchMIB();     /* initialize MIB module */
> >>                 while ( stop_requests == 0 ) {
> >>                         agent_check_and_process(1); /* 0 == don't block
> */
> >>                 }
> >>
> >>                 /* at shutdown time */
> >>                 snmp_shutdown("iotwatch");
> >>                 SOCK_CLEANUP;
> >>                 /*END SNMP*/
> >>
> >> Regards,
> >> Ulrich
> >>
> >>
> >
> >
> >
> >
> >
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