collector: Implement uname collector for FreeBSD (#1239)

* collector: Implement uname collector for FreeBSD

Signed-off-by: David O'Rourke <david.orourke@gmail.com>

collector/uname.go

@@ -0,0 +1,72 @@
+// Copyright 2019 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 freebsd linux
+// +build !nouname
+
+package collector
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var unameDesc = prometheus.NewDesc(
+	prometheus.BuildFQName(namespace, "uname", "info"),
+	"Labeled system information as provided by the uname system call.",
+	[]string{
+		"sysname",
+		"release",
+		"version",
+		"machine",
+		"nodename",
+		"domainname",
+	},
+	nil,
+)
+
+type unameCollector struct{}
+type uname struct {
+	SysName    string
+	Release    string
+	Version    string
+	Machine    string
+	NodeName   string
+	DomainName string
+}
+
+func init() {
+	registerCollector("uname", defaultEnabled, newUnameCollector)
+}
+
+// NewUnameCollector returns new unameCollector.
+func newUnameCollector() (Collector, error) {
+	return &unameCollector{}, nil
+}
+
+func (c unameCollector) Update(ch chan<- prometheus.Metric) error {
+	uname, err := getUname()
+	if err != nil {
+		return err
+	}
+
+	ch <- prometheus.MustNewConstMetric(unameDesc, prometheus.GaugeValue, 1,
+		uname.SysName,
+		uname.Release,
+		uname.Version,
+		uname.Machine,
+		uname.NodeName,
+		uname.DomainName,
+	)
+
+	return nil
+}