Re: snmp_select_info() timeout behaviour

Correction, it seems that this behaviour is actually happening even if
I set the timeout >= 15secs. However, it is after 15sec that
snmp_select_info starts this behaviour.

On Thu, Jan 19, 2012 at 2:49 PM, Joe Stringer <[email protected]> wrote:
> Greetings,
>
> I've been writing a subagent against net-snmp 5.7.1 under a 64-bit
> ubuntu linux install, based on the example subagent code
> (http://www.net-snmp.org/tutorial/tutorial-5/toolkit/demon/example-demon.c),
> using the snmp_select_info() API. In addition to handling snmp
> communication with the master, it is sending messages to a nox
> application on a regular interval, and dealing with responses from
> that socket.
>
> It seems that if select() times out after <15secs, then I call
> snmp_select_info(), it will try to set the timeout so that it will
> expire 15sec after the original call. All subsequent calls to
> snmp_select_info() set the timeout to 1usec.
>
> Example: if poll_interval_ = 14sec,
> - socket() times out after 14s, and a message is sent. I reset the
> timer to 14sec.
> - when snmp_select_info() is next passed the timer object, it resets
> the timer to ~1sec.
> - After this timeout, I reset the timer to 14sec, then
> snmp_select_info() changes the timeout to {0,1}.
> - Repeat the last step ad infinitum!
>
> Why does net-snmp do this? It seems to be fine if I set poll_interval_ >=15sec.
>
> Am I missing some API calls that I should be making?
>
> Below is the main loop of the code I'm using, followed by the output I
> see. The code beforehand is mostly the same as the example, with a
> couple of extra variable declarations, socket setup, sending an
> initial msg to noxfd.
>
> -- CODE --
>  /* Set up our timers */
>  struct timeval expire_time,timer;
>  timerclear(&timer);
>  timerclear(&expire_time);
>  timer.tv_sec = poll_interval_;
>
>  size_t len = 0;
>  while(keep_running_) {
>    FD_ZERO(&fdset);
>    FD_SET(noxfd, &fdset);
>
>    fprintf(stderr, "Timer check %d:%d\n", timer.tv_sec, timer.tv_usec);
>
>    gettimeofday(&expire_time, NULL);
>    expire_time.tv_sec += poll_interval_;
>
>    snmp_select_info(&numfds, &fdset, &timer, &block);
>
>    fprintf(stderr, "Timer check1 %d:%d\n", timer.tv_sec, timer.tv_usec);
>
>    count = select(numfds, &fdset, NULL, NULL, &timer);
>
>    if (count == 0) {
>      /* Regular stats request sending */
>      if (send(noxfd,stats_msg, strlen(stats_msg), 0) != 0)
>        snmp_log(LOG_ERR, "Failed to send stats_request");
>
>      snmp_timeout();
>      timer.tv_sec = poll_interval_;
>      timer.tv_usec = 0;
>      fprintf(stderr, "Timer reset %d:%d\n", timer.tv_sec, timer.tv_usec);
>    } else if (count > 0) {
>      /* Either nox or netsnmp has an event to deal with */
>      if(FD_ISSET(noxfd, &fdset)) {
>        if ((len = read(noxfd, buf, 2048)) > 0) {
>          parse_response(buf, len);
>        }
>
>        /* Make sure snmp_read() doesn't tinker with our noxfd */
>        FD_CLR(noxfd, &fdset);
>        --count;
>      }
>      if (count > 0) /* If there are SNMP events */
>        snmp_read(&fdset);
>
>      struct timeval current;
>      gettimeofday(&current, NULL);
>      timersub(&expire_time, &current, &timer);
>
>      fprintf(stderr, "Timer check2: %d:%d\n", timer.tv_sec, timer.tv_usec);
>    }
>  }
>
> -- OUTPUT --
> Timer check 14:0
> Timer check1 14:0
> Parsing response...
> Timer check2: 13:998949
> Timer check 13:998949
> Timer check1 13:998949
> Timer reset 14:0
> Timer check 14:0
> Timer check1 0:985627
> Timer reset 14:0
> Timer check 14:0
> Timer check1 0:1
> Timer reset 14:0
> Timer check 14:0
> Timer check1 0:1
> Timer reset 14:0
> Timer check 14:0
> Timer check1 0:1
> Timer reset 14:0
> Timer check 14:0
> ...
>
> Any help would be appreciated.
>
> Cheers,
> Joe

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