[collectd 6] df plugin: Align metrics with OpenTelemetry recommendations.

[octo]

• Fixed an error that caused inode utilization (a ratio) to be reported as "usage" (a count).
• Report utilization as "ratio" (i.e. fraction of one) instead of percentage.
• Change label names to match OpenTelemetry semantic conventions. E.g. use system.filesystem.state instead of state.
• Report the filesystem mode (read-only, read-write).

ChangeLog: DF plugin: The metric schema has been aligned with OpenTelemetry semantic conventions.

[eero-t]

Approved.

I've suggested option names that are IMHO more readable/understandable, but such change can be done in separate PR (updating also options for already merged other PRs).

[eero-t]

While I haven't complained about these in other PRs, I think these names are too similar i.e. easily confused. Adding unit to their names would make them more understandable without user needing to resort to documentation:

Suggested change

	# ReportUsage true
	# ReportUtilization false
	# UsageBytes true
	# UtilizationRatio false

What do you think?

[eero-t]

If config option names are changed, maybe these too?

Suggested change

	static bool report_usage = true;
	static bool report_utilization;
	static bool report_bytes = true;
	static bool report_ratio;

[octo]

I agree that "usage" and "utilization" can be confusing. I quite liked the old "absolute" vs. "relative" framing, that was very intuitive for me.

Absolute/relative is also much better than usage/utilization. I don't really care whether it's that, or adding units, as long as those IMHO usability-wise awful usage/utilization names are avoided.

I don't particularly like to add the unit, since I'd like to have one common set of options across all "standard" plugins.

Yes, those names should be consistent across plugins. I.e. such changes are better in separate PR that changes all relevant names.