Re: [Nagios-devel] vanished bug numbers in the nagios mantis tracker

[Andreas E. <ae...@op...>]

On 08/07/2012 10:22 PM, William Leibzon wrote:
> On Tue, Aug 7, 2012 at 12:56 PM, Andreas Ericsson <ae...@op...> wrote:
> 
>> On 08/07/2012 07:24 PM, Jochen Bern wrote:
>>> On 08/07/2012 03:21 PM, Andreas Ericsson wrote:
>>>> [...] Each module gets to keep its own data and Nagios doesn't need to
>>>> know anything at all about it (although it would be neat if it could
>>>> issue a callback and get a key/value vector when printing status data).
>>> [...]
>>>> It would ofcourse be nifty if modules *did* know about each other's
>>>> data, assuming they explicitly request it, but that's not what you're
>>>> talking about so let's ignore that for now.
>>>
>>> FWIW (and not that I've ever coded such a thing myself), if two modules
>>> would *want* to share data, all they would need beyond the OS' shared
>>> memory support would be unique module IDs, a means to coordinate startup
>>> priority (so that the module that actually *creates* the shared memory
>>> can do so before the "user" modules ask for it), and a means of
>>> user-module---to-nagios-core---to-creator-module "hey creator module,
>>> hand me the necessary access data!" requests. Assuming that there are no
>>> "malevolent" modules you have to protect the same data against, that is.
>>>
>>
>> That is over the top. The idea suggested by John is really good to find
>> random module pointers. The using module needs to know about the data
>> from the module it uses anyway, and a one-time lookup from all loaded
>> modules is no big deal. And the list is already there, btw.
>>
>> So we'd add something like
>>
>>    void *nebmod_get_ancillary_data(const char *module_id);
>>    int nebmod_set_ancillary_data(const char *module_id, const void *ptr);
>>
>> to nagios core. The writing module uses the set call. The reader
>> module uses the get call. Both provide the same module_id and the rest
>> happens automagically.
> 
> 
> I think we need more than this. First of even going with above two calls
> backs, the call syntax is just not enough - need to be able to ask for data
> pertaining to specific service/host/etc and not just by some id. And I'd
> rather not have to make an extra call back to get an ephemeral id.
> 

The ancillary data from one module will ofcourse contain the indexed arrays
with information on all hosts and services.

> That's why I agree with original thoughts of being able to add "named"
> extra data to service/host/etc. And this is not just for use of one module
> but something that other modules are expected to be able to ask for. This
> allows to extend nagios with modules rather than adding features into core
> which is a right way into the future. In fact I'd go as far as advocating
> allowing modules to add new config parameters in the future i.e.
> registering callback function to process "newconfig = ..." parameters.
> 
> And as far as ordering, I don't think it is a big issue. All that is needed
> is for nagios to provide a list of loaded or loaded-to-be modules and this
> is already created by nagios before modules are loaded. Most of the time
> we'll have one module creating extra data and several others who would be
> using/reading it; and reading should then happen after initiation when data
> is there. Rare case when two modules may want to modify the same data
> should either be avoided entirely or synchronization left to those writing
> such modules with additional parameters to be passed that specify ordering,
> etc.
> 

That would still mean linked-list traversal and X strcmp() calls for each
module that wants to get ancillary data on some object. Please keep in
mind that this is expected to happen about 5000 times per second for a
large network, so awesome performance is an absolute requirement rather
than something that would be nice to have.

-- 
Andreas Ericsson                   and...@op...
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

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