Add a new riemann-hwmon tool for harware monitors

hwmon is a Linux interface to access harware monitors such as the
temperature of devices, input voltage, and so on.

This tool rely on the files exposed by the sysfs filesystem.

bin/riemann-hwmon

@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+Process.setproctitle($PROGRAM_NAME)
+
+require 'riemann/tools/hwmon'
+
+Riemann::Tools::Hwmon.run

lib/riemann/tools/hwmon.rb

@@ -0,0 +1,131 @@
+# frozen_string_literal: true
+
+require 'riemann/tools'
+
+# See https://www.kernel.org/doc/html/latest/hwmon/index.html
+module Riemann
+  module Tools
+    class Hwmon
+      include Riemann::Tools
+
+      class Device
+        attr_reader :hwmon, :type, :number, :crit, :lcrit, :label, :name
+
+        def initialize(hwmon, type, number)
+          @hwmon = hwmon
+          @type = type
+          @number = number
+
+          @crit = scale(read_hwmon_i('crit'))
+          @lcrit = scale(read_hwmon_i('lcrit'))
+          @label = read_hwmon_s('label')
+          @name = read_hwmon_file('name')
+        end
+
+        def input
+          read_hwmon_i('input')
+        end
+
+        def report
+          value = scale(input)
+
+          state = :ok
+          state = :critical if crit && value >= crit
+          state = :critical if lcrit && value <= lcrit
+          {
+            service: "hwmon #{name} #{label}",
+            state: state,
+            metric: value,
+            description: fromat_input(value),
+          }
+        end
+
+        private
+
+        def scale(value)
+          return nil if value.nil?
+
+          case type
+          when :fan then value.to_i # rpm
+          when :in, :temp, :curr then value.to_f / 1000 # mV, m°C, mA
+          when :humidity then value.to_f / 100 # %H
+          when :power, :energy then value.to_f / 1_000_000 # uW, uJ
+          end
+        end
+
+        def fromat_input(value)
+          case type
+          when :in then format('%<value>.3f V', { value: value })
+          when :fan then "#{value} RPM"
+          when :temp then format('%<value>.3f °C', { value: value })
+          when :curr then format('%<value>.3f A', { value: value })
+          when :power then format('%<value>.3f W', { value: value })
+          when :energy then format('%<value>.3f J', { value: value })
+          when :humidity then format('%<value>d %H', { value: (value * 100).to_i })
+          end
+        end
+
+        def read_hwmon_i(file)
+          s = read_hwmon_s(file)
+          return nil if s.nil?
+
+          s.to_i
+        end
+
+        def read_hwmon_s(file)
+          read_hwmon_file("#{type}#{number}_#{file}")
+        end
+
+        def read_hwmon_file(file)
+          File.read("/sys/class/hwmon/hwmon#{hwmon}/#{file}").chomp
+        rescue Errno::ENOENT
+          nil
+        end
+      end
+
+      FIRST_NUMBER = {
+        in: 0,
+        fan: 1,
+        temp: 1,
+        curr: 1,
+        power: 1,
+        energy: 1,
+        humidity: 1,
+      }.freeze
+
+      attr_reader :devices
+
+      def initialize
+        super
+
+        @devices = poll_devices
+      end
+
+      def poll_devices
+        res = []
+
+        hwmon = 0
+        while File.exist?("/sys/class/hwmon/hwmon#{hwmon}")
+          %i[in fan temp curr power energy humidity].each do |type|
+            number = FIRST_NUMBER[type]
+            while File.exist?("/sys/class/hwmon/hwmon#{hwmon}/#{type}#{number}_input")
+              res << Device.new(hwmon, type, number)
+
+              number += 1
+            end
+          end
+
+          hwmon += 1
+        end
+
+        res
+      end
+
+      def tick
+        devices.each do |device|
+          report(device.report)
+        end
+      end
+    end
+  end
+end

spec/riemann/tools/hwmon/device_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'riemann/tools/hwmon'
+
+RSpec.describe Riemann::Tools::Hwmon::Device do
+  subject { described_class.new(1, :temp, 2) }
+
+  before do
+    allow(File).to receive(:read).with('/sys/class/hwmon/hwmon1/name').and_return("i350bb\n")
+    allow(File).to receive(:read).with('/sys/class/hwmon/hwmon1/temp2_input').and_return("#{input}\n")
+    allow(File).to receive(:read).with('/sys/class/hwmon/hwmon1/temp2_crit').and_return("96000\n")
+    allow(File).to receive(:read).with('/sys/class/hwmon/hwmon1/temp2_lcrit').and_raise(Errno::ENOENT)
+    allow(File).to receive(:read).with('/sys/class/hwmon/hwmon1/temp2_label').and_return("loc1\n")
+  end
+
+  describe '#report' do
+    context 'when temperature is ok' do
+      let(:input) { 31_000 }
+
+      it { expect(subject.report).to eq({ service: 'hwmon i350bb loc1', state: :ok, metric: 31.0, description: '31.000 °C' }) }
+    end
+
+    context 'when temperature is critical' do
+      let(:input) { 96_000 }
+
+      it { expect(subject.report).to eq({ service: 'hwmon i350bb loc1', state: :critical, metric: 96.0, description: '96.000 °C' }) }
+    end
+  end
+end