Add kstat-based Solaris metrics (#1197)

* collector/loadavg_solaris.go: Use libkstat to gather load averages.
* go.mod: Added go-kstat.
* boot_time_solaris.go: Added.
* cpu_solaris.go: Added.
* README.md: Updated entries for Solaris.
* collector/zfs_solaris.go: Added.
* CHANGELOG.md: Added note about kstat-based Solaris metrics.

Signed-off-by: Jonathan Davies <jpds@protonmail.com>

collector/boot_time_solaris.go

@@ -0,0 +1,66 @@
+// Copyright 2018 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 solaris
+// +build !noboottime
+
+package collector
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/siebenmann/go-kstat"
+)
+
+type bootTimeCollector struct {
+	boottime typedDesc
+}
+
+func init() {
+	registerCollector("boottime", defaultEnabled, newBootTimeCollector)
+}
+
+func newBootTimeCollector() (Collector, error) {
+	return &bootTimeCollector{
+		boottime: typedDesc{
+			prometheus.NewDesc(
+				prometheus.BuildFQName(namespace, "", "boot_time_seconds"),
+				"Unix time of last boot, including microseconds.",
+				nil, nil,
+			), prometheus.GaugeValue},
+	}, nil
+}
+
+// newBootTimeCollector returns a new Collector exposing system boot time on Solaris systems.
+// Update pushes boot time onto ch
+func (c *bootTimeCollector) Update(ch chan<- prometheus.Metric) error {
+	tok, err := kstat.Open()
+	if err != nil {
+		return err
+	}
+
+	defer tok.Close()
+
+	ks, err := tok.Lookup("unix", 0, "system_misc")
+	if err != nil {
+		return err
+	}
+
+	v, err := ks.GetNamed("boot_time")
+	if err != nil {
+		return err
+	}
+
+	ch <- c.boottime.mustNewConstMetric(float64(v.UintVal))
+
+	return nil
+}