ctlstat: add prometheus output

[asomers]

Summary

When invoked by inetd, ctlstat -P will now produce output suitable for
ingestion into Prometheus.

It's a drop-in replacement for https://github.com/Gandi/ctld_exporter,
except that it doesn't report the number of initiators per target, and
it does report time and dma_time.

MFC after: 2 weeks
Sponsored by: Axcient

[0mp]

I've got some minor fixes for the manual page.

Also, just an idea: shouldn't we extend libxo with Prometheus support? This way we would have a consistent way of printing this format across various utilities without having to introduce a different flag for each one.

usr.bin/ctlstat/ctlstat.8

90

136

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[asomers]

• Respond to 0mp's man page review

[asomers]

In D29901#671164, @0mp wrote:

I've got some minor fixes for the manual page.

Also, just an idea: shouldn't we extend libxo with Prometheus support? This way we would have a consistent way of printing this format across various utilities without having to introduce a different flag for each one.

That's an interesting idea. I hadn't thought of it. The only problems are that I'm not very familiar with libxo's workings, and ctlstat doesn't support libxo anyway. I admit, I'm not thrilled about the idea of repeating all of this work. But it might be worthwhile. Do you know libxo? What would your proposal entail?

[bapt]

Note: prometheus output is quite specific, I am not sure it is worth trying to add libxo to the party. Having a half backed conversion to libxo just to cover prom sounds weird to me.

[bcr]

Manpage looks good now.