Sysctl as a Service, or: making sysctl(3) more friendly for monitoring systems

[Peter Jeremy]

On 2016-Dec-12 17:57:07 -0700, Warner Losh <imp at bsdimp.com> wrote:
>On Mon, Dec 12, 2016 at 6:34 AM, Ed Schouten <ed at nuxi.nl> wrote:
>> $ time ./prometheus_sysctl_exporter | wc -l
>>         0.00 real         0.00 user         0.00 sys
>>     3162
>>
>> If our sysctl tree would get substantially larger at some point, we
>> should of course revisit this.
>
>That sounds cool. I'd love to see what you came up with to get those results.

I think that's impressive as well.

>While we're here... there's one thing I'd love to see from  a
>hypothetical /dev/sysctl... When a sysctl value changes (or some
>subset), I'd like it to appear on a read-channel. That way, I could
>monitor temperature w/o needing to constantly poll for changes, for
>example.

That sounds like a job for kqueue(2), though it would need to be plumbed
through.  The biggest problem I see is that nothing in the sysctl mechanism
has any way of reporting that a value has changed and so consumers of that
data should re-check.  This means that you'd probably just wind up polling
in the kernel.

Note that Prometheus is designed around regularly polling the systems it's
monitoring so this sort of functionality wouldn't benefit it.

-- 
Peter Jeremy
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