a crude script for exporting device-mapper stats from dmsetup status to prometheus

dm-status.sh

#!/bin/bash

prefix="device_mapper_status"

d_echo() {
    #echo "$@" >&2
    true
}

CACHE_FIELDS_FIXED="
    meta_block_size meta_blocks_used meta_blocks_total
    cache_block_size cache_blocks_used cache_blocks_total
    read_hits read_misses write_hits write_misses
    demotions promotions dirty
"

scrape_target_cache() {
    local labels="$1"
    local stats=$(tr '/' ' ')
    set -- $stats

    for field in $CACHE_FIELDS_FIXED; do
        val="$1"
        shift
        echo "${prefix}_${field}{${labels}} ${val}"
    done
    # features
    feature_cnt="$1"
    shift
    for ((i=feature_cnt; i > 0; i--)); do
        feature="$1"
        shift
        echo "${prefix}_feature{${labels},feature=\"$feature\"} 1"
    done
    # core args
    core_cnt="$1"
    shift
    for ((i=core_cnt; i > 0; i-=2)); do
        key="$1"
        val="$2"
        shift 2
        echo "${prefix}_core_arg{${labels},arg=\"$key\"} $val"
    done
    # policy
    policy_name="$1"
    shift
    echo "${prefix}_policy{${labels},policy_name=\"${policy_name}\"} 1"
    # policy args
    policy_cnt="$1"
    shift
    for ((i=policy_cnt; i > 0; i-=2)); do
        key="$1"
        val="$2"
        shift 2
        echo "${prefix}_policy_arg{${labels},arg=\"$key\"} $val"
    done
    # meta_mode, needs_check
    meta_mode="$1"
    shift
    for mode in rw ro; do
       val=0
       if [ "$mode" = "$meta_mode" ]; then
           val=1
       fi
       echo "${prefix}_meta_mode{${labels},mode=\"$mode\"} ${val}"
    done
    needs_check="$1"
    shift
    if [ "$needs_check" = "-" ]; then
        needs_check_val=0
    else
        needs_check_val=1
    fi
    echo "${prefix}_needs_check{${labels}} ${needs_check_val}"
    # should be nothing left
    echo "$@" |scrape_unk_target "$labels"
}

scrape_unk_target() {
    local labels="$1"
    local unk_args=$(wc -w)
    echo "${prefix}_unknown_status_vals{${labels}} ${unk_args}"
}

scrape_device() {
    local dev="$1"
    while read start len type stats; do
        local fun="scrape_target_${type}"
        if [ "$(type -t $fun)" != "function" ]; then
            d_echo "no stats for $type"
            fun=scrape_unk_target
        fi
        local labels="dev=\"${dev}\",offset=\"${start}\",type=\"${type}\""
        echo "$stats" |$fun "$labels"
    done < <(dmsetup status "$dev")
}

for f in /dev/mapper/*; do
    dev=$(basename "$f")
    if [ "$dev" = "control" ]; then
        continue
    fi
    d_echo "$dev" >&2
    scrape_device "$dev"
done

prometheus-node-exporter-dm-status.service

[Unit]
Description=Collect device-mapper metrics for prometheus-node-exporter

[Service]
Type=oneshot
Environment=TMPDIR=/var/lib/prometheus/node-exporter
Environment=LC_ALL=C

prometheus-node-exporter-dm-status.timer

[Unit]
Description=Run dm-status metrics collection every 30 seconds
ConditionPathExists=/usr/sbin/dmsetup
ConditionPathExistsGlob=|/dev/mapper/*

[Timer]
OnBootSec=0
OnUnitActiveSec=30s

[Install]
WantedBy=timers.target