ZFS collector uses different names for the same metric on FreeBSD vs Linux

Host operating system: output of uname -a

• FreeBSD shoebox 12.2-RELEASE-p2 FreeBSD 12.2-RELEASE-p2 663e6b09467(HEAD) TRUENAS amd64
• Linux ishtar 5.8.0-40-generic #45-Ubuntu SMP Fri Jan 15 11:05:36 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

node_exporter version: output of node_exporter --version

I'm using the packaged versions for FreeBSD 12 (latest) and Ubuntu 20.10

node_exporter, version 1.0.1 (branch: release-1.0, revision: 0)
  build user:       root
  build date:
  go version:       go1.15.6

node_exporter, version 1.0.1+ds (branch: debian/sid, revision: 1.0.1+ds-1)
  build user:       pkg-go-maintainers@lists.alioth.debian.org
  build date:       20200618-22:00:01
  go version:       go1.14.4

node_exporter command line flags

FreeBSD: --web.listen-address=172.17.3.5:9100 --collector.textfile.directory=/var/tmp/node_exporter --collector.zfs
Linux: (none, using defaults)

Are you running node_exporter in Docker?

No

What did you do that produced an error?

Ran node_exporter, collecting ZFS metrics on both Linux and FreeBSD

What did you expect to see?

Metrics would have the same name (I think that's the right term?) from both nodes.

What did you see instead?

The names of metrics exported from FreeBSD are different from the ones from Linux.

Extra Comments

The FreeBSD system is more precisely running TrueNAS, but it's close enough to FreeBSD that it doesn't make a big difference. The FreeBSD system is using OpenZFS 2.0, while the Linux system is using ZFSonLinux 0.8.4 (same project, they're skipping 1.0 while unifying the different OSs to a single codebase), so they're close enough that it shouldn't make a difference.

The FreeBSD ZFS collector is modifying the names that it's reading from sysctl, while the Linux ZFS collector seems to be basically dumping the contents of /proc/spl/kstat/zfs/*, munging the names so that they fit the proper naming scheme.

Start with collector/zfs_freebsd.go, especially the metric-name handling linked in the issue, and compare it with the Linux collector's reading of /proc/spl/kstat/zfs/*. Run node_exporter with the ZFS collector on both FreeBSD and Linux, then verify that equivalent ZFS metrics are exported under the same names.