ZFS: io stats removed

Host operating system:

OpenZFS as of commit https://github.com/openzfs/zfs/commit/371f88d96fe0aeb46a72fec78f90e1d777493ee5

node_exporter version

$ /usr/bin/prometheus-node-exporter --version
node_exporter, version 0.17.0+ds (branch: debian/sid, revision: 0.17.0+ds-3+b11)
  build user:       pkg-go-maintainers@lists.alioth.debian.org
  build date:       20190608-10:00:14
  go version:       go1.11.6

...through to master, current HEAD (3762191e66e3)

node_exporter command line flags

--collector.zfs

What did you do that produced an error?

Upgraded to OpenZFS HEAD https://github.com/openzfs/zfs/commit/HEAD

What did you expect to see?

$ wget -qO - http://server:9100/metrics | grep ^node_zfs_zpool || echo "NOT FOUND"
node_zfs_zpool_nread{zpool="pool"} 2.49897949175808e+14
node_zfs_zpool_nwritten{zpool="pool"} 2.65591973699584e+14
node_zfs_zpool_rcnt{zpool="pool"} 0
node_zfs_zpool_reads{zpool="pool"} 2.729451643e+09
node_zfs_zpool_rlentime{zpool="pool"} 4.728605718663304e+16
node_zfs_zpool_rtime{zpool="pool"} 5.775579362149045e+15
node_zfs_zpool_rupdate{zpool="pool"} 1.3886342123071748e+16
node_zfs_zpool_wcnt{zpool="pool"} 0
node_zfs_zpool_wlentime{zpool="pool"} 2.8960276949205395e+17
node_zfs_zpool_writes{zpool="pool"} 3.436014883e+09
node_zfs_zpool_wtime{zpool="pool"} 1.319409654928622e+15
node_zfs_zpool_wupdate{zpool="pool"} 1.3886342121834806e+16

What did you see instead?

$ wget -qO - http://server:9100/metrics | grep ^node_zfs_zpool || echo "NOT FOUND"
NOT FOUND

Node_exporter uses /proc/spl/kstat/zfs/*/io to collect these stats. This proc file has been removed as of OpenZFS https://github.com/openzfs/zfs/commit/371f88d96fe0aeb46a72fec78f90e1d777493ee5.

See Also: https://github.com/openzfs/zfs/pull/12212

Start by reviewing node_exporter's ZFS collector behavior around /proc/spl/kstat/zfs/*/io and the referenced OpenZFS commit and pull request. Determine how the removed source affects the expected node_zfs_zpool metrics, then verify that the metrics are restored with the --collector.zfs path and the provided wget query.