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

[Warner Losh]

> On Dec 12, 2016, at 10:27 PM, Peter Jeremy <peter at rulingia.com> wrote:
> 
> 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.

It does if you had a read-channel :)

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

True.

Warner

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