Re: How to force a cache reload when dynamic interfaces

On Wed, 2005-11-23 at 10:41 -0600, Emi.Yanagi@radisys.com wrote:
> I want to trigger a cache reload only when
> dynamic interfaces creating/removing happen.

Let's be clear about exactly what you mean here.
By "dynamic", do you mean in response to explicit SNMP
SET requests, or when an interface is physically added
to (or removed from) the system?


If you mean the first, then you probably shouldn't be
using the cache mechanism at all. The agent would most
naturally hold the table representation internally, so
could add or remove entries as required.
The main role of the cache processing is to link the
agent's view with what's actually happening in the
underlying system (assuming these are different). If
your MIB table is purely driven via SNMP SET requests,
then the agent *is* the "underlying system", so caching
isn't necessary.


If the underlying system is separate, and you want the
agent to refresh its internal representation automatically
when this underlying system changes, then you'll need to
find a way of signalling to the agent when this happens.
(e.g. call the cache_load routine directly)


> So I tried to
> call the cache load routine directly when dynamic interfaces
> creating/removing happen.

Yup - that sounds like the right approach.


> The problem is I got the Error: OID not increasing:
>
> $snmpwalk 10.1 ifIndex
> IF-MIB::ifIndex.1 = INTEGER: 1
> IF-MIB::ifIndex.2 = INTEGER: 2
> IF-MIB::ifIndex.3 = INTEGER: 3
> IF-MIB::ifIndex.4 = INTEGER: 4
> IF-MIB::ifIndex.4 = INTEGER: 4
> Error: OID not increasing: IF-MIB::ifIndex.4
> >= IF-MIB::ifIndex.4

I don't think that's related to how the table data is cached
(or not). It feels more concerned with how the table data
is *walked* - in particular, to the processing of the last
entry.


> My questions are:
> What is the proper way to force a cache reload at anytime?

Call the cache_load routine.
That's exactly what it's there for.

> Do I need to register a separate cache handler to do this?

No. In fact, you probably don't need to register the
table as explicitly using the cache handler at all.
That's really aimed at loading the cache "on demand",
in response to incoming GET* requests. If you want
complete control over exactly when the cache is
reloaded, it's probably easier not to have the cache
helper in the handler chain.


Dave


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