RFR: Initial support for ZFS on FreeBSD (#1224)

* WIP: Initial support for ZFS on FreeBSD

* Added build directives

* Ignore 'kstatPath' config option on FreeBSD

* Added tests for ZFS FreeBSD input plugin.

* Updated the README to confrom with the guidelines and added FreeBSD info

* Fixed indents

* Spell check

plugins/inputs/zfs/zfs_linux.go

@@ -0,0 +1,131 @@
+// +build linux
+
+package zfs
+
+import (
+	"fmt"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/plugins/inputs"
+)
+
+type poolInfo struct {
+	name       string
+	ioFilename string
+}
+
+func getPools(kstatPath string) []poolInfo {
+	pools := make([]poolInfo, 0)
+	poolsDirs, _ := filepath.Glob(kstatPath + "/*/io")
+
+	for _, poolDir := range poolsDirs {
+		poolDirSplit := strings.Split(poolDir, "/")
+		pool := poolDirSplit[len(poolDirSplit)-2]
+		pools = append(pools, poolInfo{name: pool, ioFilename: poolDir})
+	}
+
+	return pools
+}
+
+func getTags(pools []poolInfo) map[string]string {
+	var poolNames string
+
+	for _, pool := range pools {
+		if len(poolNames) != 0 {
+			poolNames += "::"
+		}
+		poolNames += pool.name
+	}
+
+	return map[string]string{"pools": poolNames}
+}
+
+func gatherPoolStats(pool poolInfo, acc telegraf.Accumulator) error {
+	lines, err := internal.ReadLines(pool.ioFilename)
+	if err != nil {
+		return err
+	}
+
+	if len(lines) != 3 {
+		return err
+	}
+
+	keys := strings.Fields(lines[1])
+	values := strings.Fields(lines[2])
+
+	keyCount := len(keys)
+
+	if keyCount != len(values) {
+		return fmt.Errorf("Key and value count don't match Keys:%v Values:%v", keys, values)
+	}
+
+	tag := map[string]string{"pool": pool.name}
+	fields := make(map[string]interface{})
+	for i := 0; i < keyCount; i++ {
+		value, err := strconv.ParseInt(values[i], 10, 64)
+		if err != nil {
+			return err
+		}
+		fields[keys[i]] = value
+	}
+	acc.AddFields("zfs_pool", fields, tag)
+
+	return nil
+}
+
+func (z *Zfs) Gather(acc telegraf.Accumulator) error {
+	kstatMetrics := z.KstatMetrics
+	if len(kstatMetrics) == 0 {
+		kstatMetrics = []string{"arcstats", "zfetchstats", "vdev_cache_stats"}
+	}
+
+	kstatPath := z.KstatPath
+	if len(kstatPath) == 0 {
+		kstatPath = "/proc/spl/kstat/zfs"
+	}
+
+	pools := getPools(kstatPath)
+	tags := getTags(pools)
+
+	if z.PoolMetrics {
+		for _, pool := range pools {
+			err := gatherPoolStats(pool, acc)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	fields := make(map[string]interface{})
+	for _, metric := range kstatMetrics {
+		lines, err := internal.ReadLines(kstatPath + "/" + metric)
+		if err != nil {
+			return err
+		}
+		for i, line := range lines {
+			if i == 0 || i == 1 {
+				continue
+			}
+			if len(line) < 1 {
+				continue
+			}
+			rawData := strings.Split(line, " ")
+			key := metric + "_" + rawData[0]
+			rawValue := rawData[len(rawData)-1]
+			value, _ := strconv.ParseInt(rawValue, 10, 64)
+			fields[key] = value
+		}
+	}
+	acc.AddFields("zfs", fields, tags)
+	return nil
+}
+
+func init() {
+	inputs.Add("zfs", func() telegraf.Input {
+		return &Zfs{}
+	})
+}