prometheus-node-exporter-lua: add basic hwmon exporter

This collector supports following metrics:

 * node_hwmon_temp_celsius
 * node_hwmon_pwm

and following auxiliary mappings:

 * node_hwmon_chip_names
 * node_hwmon_sensor_label

Tested on:

 * Banana Pi BPI-r3 / OpenWrt 23.05.0-rc2
 * TP-Link Archer C7 v5 / OpenWrt 22.03.5

Signed-off-by: Ivan Mironov <mironov.ivan@gmail.com>

utils/prometheus-node-exporter-lua/Makefile

@@ -103,6 +103,17 @@ define Package/prometheus-node-exporter-lua-hostapd_ubus_stations/install
 	$(INSTALL_BIN) ./files/usr/lib/lua/prometheus-collectors/hostapd_ubus_stations.lua $(1)/usr/lib/lua/prometheus-collectors/
 endef
 
+define Package/prometheus-node-exporter-lua-hwmon
+  $(call Package/prometheus-node-exporter-lua/Default)
+  TITLE+= (hwmon collector)
+  DEPENDS:=prometheus-node-exporter-lua +luci-lib-nixio
+endef
+
+define Package/prometheus-node-exporter-lua-hwmon/install
+	$(INSTALL_DIR) $(1)/usr/lib/lua/prometheus-collectors
+	$(INSTALL_BIN) ./files/usr/lib/lua/prometheus-collectors/hwmon.lua $(1)/usr/lib/lua/prometheus-collectors/
+endef
+
 define Package/prometheus-node-exporter-lua-ltq-dsl
   $(call Package/prometheus-node-exporter-lua/Default)
   TITLE+= (lantiq dsl collector)
@@ -240,6 +251,7 @@ $(eval $(call BuildPackage,prometheus-node-exporter-lua-bmx7))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-dawn))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-hostapd_stations))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-hostapd_ubus_stations))
+$(eval $(call BuildPackage,prometheus-node-exporter-lua-hwmon))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-ltq-dsl))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-nat_traffic))
 $(eval $(call BuildPackage,prometheus-node-exporter-lua-netstat))

utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/hwmon.lua

@@ -0,0 +1,58 @@
+#!/usr/bin/lua
+
+local fs = require "nixio.fs"
+
+local function rtrim(s)
+  return string.gsub(s, "\n$", "")
+end
+
+local function scrape()
+  local metric_chip_names = metric("node_hwmon_chip_names", "gauge")
+  local metric_sensor_label = metric("node_hwmon_sensor_label", "gauge")
+  local metric_temp_celsius = metric("node_hwmon_temp_celsius", "gauge")
+  local metric_pwm = metric("node_hwmon_pwm", "gauge")
+
+  for hwmon_path in fs.glob("/sys/class/hwmon/hwmon*") do
+    -- Produce node_hwmon_chip_names
+    -- See https://github.com/prometheus/node_exporter/blob/7c564bcbeffade3dacac43b07c2eeca4957ca71d/collector/hwmon_linux.go#L415
+    local chip_name = rtrim(get_contents(hwmon_path .. "/name"))
+    if chip_name == "" then
+      chip_name = fs.basename(hwmon_path)
+    end
+
+    -- See https://github.com/prometheus/node_exporter/blob/7c564bcbeffade3dacac43b07c2eeca4957ca71d/collector/hwmon_linux.go#L355
+    local chip = chip_name
+    local real_dev_path, status = fs.realpath(hwmon_path .. "/device")
+    if not status then
+      local dev_name = fs.basename(real_dev_path)
+      local dev_type = fs.basename(fs.dirname(real_dev_path))
+      chip = dev_type .. "_" .. dev_name
+    end
+    metric_chip_names({chip=chip, chip_name=chip_name}, 1)
+
+    -- Produce node_hwmon_sensor_label
+    for sensor_path in fs.glob(hwmon_path .. "/*_label") do
+      local sensor = string.gsub(fs.basename(sensor_path), "_label$", "")
+      local sensor_label = rtrim(get_contents(sensor_path))
+      metric_sensor_label({chip=chip, sensor=sensor, label=sensor_label}, 1)
+    end
+
+    -- Produce node_hwmon_temp_celsius
+    for sensor_path in fs.glob(hwmon_path .. "/temp*_input") do
+      local sensor = string.gsub(fs.basename(sensor_path), "_input$", "")
+      local temp = get_contents(sensor_path) / 1000
+      metric_temp_celsius({chip=chip, sensor=sensor}, temp)
+    end
+
+    -- Produce node_hwmon_pwm
+    for sensor_path in fs.glob(hwmon_path .. "/pwm*") do
+      local sensor = fs.basename(sensor_path)
+      if string.match(sensor, "^pwm[0-9]+$") then
+        local pwm = rtrim(get_contents(sensor_path))
+        metric_pwm({chip=chip, sensor=sensor}, pwm)
+      end
+    end
+  end
+end
+
+return { scrape = scrape }