add diskstats on Darwin (#593)

* Add diskstats collector for Darwin

* Update year in the header

* Update README.md

* Add github.com/lufia/iostat to vendored packages

* Change stats to follow naming guidelines

* Add a entry of github.com/lufia/iostat into vendor.json

* Remove /proc/diskstats from description

collector/diskstats_darwin.go

@@ -0,0 +1,177 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !nodiskstats
+
+package collector
+
+import (
+	"fmt"
+
+	"github.com/lufia/iostat"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	diskSubsystem = "disk"
+)
+
+type typedDescFunc struct {
+	typedDesc
+	value func(stat *iostat.DriveStats) float64
+}
+
+type diskstatsCollector struct {
+	descs []typedDescFunc
+}
+
+func init() {
+	Factories["diskstats"] = NewDiskstatsCollector
+}
+
+// NewDiskstatsCollector returns a new Collector exposing disk device stats.
+func NewDiskstatsCollector() (Collector, error) {
+	var diskLabelNames = []string{"device"}
+
+	return &diskstatsCollector{
+		descs: []typedDescFunc{
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "reads_completed_total"),
+						"The total number of reads completed successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.NumRead)
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "read_sectors_total"),
+						"The total number of sectors read successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.NumRead) / float64(stat.BlockSize)
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "read_seconds_total"),
+						"The total number of seconds spent by all reads.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return stat.TotalReadTime.Seconds()
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "writes_completed_total"),
+						"The total number of writes completed successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.NumWrite)
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "written_sectors_total"),
+						"The total number of sectors written successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.NumWrite) / float64(stat.BlockSize)
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "write_seconds_total"),
+						"This is the total number of seconds spent by all writes.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return stat.TotalWriteTime.Seconds()
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "read_bytes_total"),
+						"The total number of bytes read successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.BytesRead)
+				},
+			},
+			{
+				typedDesc: typedDesc{
+					desc: prometheus.NewDesc(
+						prometheus.BuildFQName(Namespace, diskSubsystem, "written_bytes_total"),
+						"The total number of bytes written successfully.",
+						diskLabelNames,
+						nil,
+					),
+					valueType: prometheus.CounterValue,
+				},
+				value: func(stat *iostat.DriveStats) float64 {
+					return float64(stat.BytesWritten)
+				},
+			},
+		},
+	}, nil
+}
+
+func (c *diskstatsCollector) Update(ch chan<- prometheus.Metric) error {
+	diskStats, err := iostat.ReadDriveStats()
+	if err != nil {
+		return fmt.Errorf("couldn't get diskstats: %s", err)
+	}
+
+	for _, stats := range diskStats {
+		for _, desc := range c.descs {
+			v := desc.value(stats)
+			ch <- desc.mustNewConstMetric(v, stats.Name)
+		}
+	}
+	return nil
+}