On Wed, 2006-01-11 at 13:01 +0200, Makavy, Erez (Erez) wrote:
> 1) When you stated "Sending traps is either done as part of processing
> SNMP requests",
> do you mean processing an agentX Notification PDU from a sub-agent?
That's one example, certainly.
> 1a) is there any other SNMP request processing which will invoke the
> master agent trap sending?
A SET request could potentially trigger a trap - either directly
(see agent/mibgroup/examples/notification.c) or implicitly (e.g
setting ifAdminStatus to down)
A GET* request could involve the re-loading of cached data, which
might trigger a trap (e.g. if this revealed that ifOperStatus
had switched to down)
That's just off the top of my head - I'm sure there are
other possible scenarios.
> 2) By mentioning the "Event Loop", do you refer to a loop on the
> agent_check_and_process() function [in snmp_agent.c] ?
No - because agent_check_and_process() doesn't involve a loop.
I mean the 'while (netsnmp_running)' loop in snmpd.c:receive().
> 2a) How does an alarm interupt this loop? (i see in
> agent_check_and_process(), you call run_alarms() synchroniously)
I'm not sure of the exact mechanism (and don't have time to check)
but I believe it involves signals, and catching SIGALRM.
Check the code.
> 2b) Alarm mechanism is seperate for Master agent and for each
> sub-agent, right?
Yes. They're separate processes, so alarms, etc are handling
independently.
> 2c) each agent has it's own request processing loop?
Yes.
> 3) A burst of traps can be generated by a sub-agent (without using the
> alarm mechanism).
> This will cause the socket that the master is listening on, to always
> full.
> (assuming assumption in quesiton 2 is right)
> I see also that _sess_read() is called for which socket which is
> ready.
> It looks like _sess_read(), processes all packets before returning.
> 3a) Is this true?
I believe so, yes.
Don't take that as gospel, though - it's a while since I looked at this
code in detail. It would not surprise me if a subagent could flood the
master agent with traps. Separating out trap processing and request
processing is probably the obvious first candidate for making the agent
multi-threaded.
But don't hold your breath!
Dave
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