On the systems on which I tested this exporter, I never ran into metrics
that were named in such a way that they couldn't be exported to
Prometheus metrics directly. Now it turns out that on systems with NUMA,
the sysctl tree contains metrics named dev.${driver}.${index}.%domain.
For these metrics, the % in the name is problematic, as Prometheus
doesn't allow this symbol to be used.
Remove the assertions that were originally put in place to prevent the
exporter from generating malformed output and add code to deal with it
accordingly. For metric names, convert any unsupported character to an
underscore. For label values, perform string escaping.
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221035
Reported by: lifanov@
c71eb5ab1f