Include DEVLINKS in available diskio udev properties (influxdata#5116)

plugins/inputs/diskio/README.md

@@ -19,6 +19,10 @@ The diskio input plugin gathers metrics about disk traffic and timing.
   ## Currently only Linux is supported via udev properties. You can view
   ## available properties for a device by running:
   ## 'udevadm info -q property -n /dev/sda'
+  ## Note: Most, but not all, udev properties can be accessed this way. Properties
+  ## that are currently inaccessible include DEVTYPE, DEVNAME, and DEVPATH. 
+  ## DEVLINKS, however, can be used as a tag as of Telegraf 1.10
+  ## For more info see https://github.com/influxdata/telegraf/issues/3663
   # device_tags = ["ID_FS_TYPE", "ID_FS_USAGE"]
   #
   ## Using the same metadata source as device_tags, you can also customize the

plugins/inputs/diskio/diskio_linux.go

@@ -2,6 +2,7 @@ package diskio
 
 import (
 	"bufio"
+	"bytes"
 	"fmt"
 	"os"
 	"strings"
@@ -52,9 +53,21 @@ func (s *DiskIO) diskInfo(devName string) (map[string]string, error) {
 	defer f.Close()
 
 	scnr := bufio.NewScanner(f)
+	var devlinks bytes.Buffer
 	for scnr.Scan() {
 		l := scnr.Text()
-		if len(l) < 4 || l[:2] != "E:" {
+		if len(l) < 4 {
+			continue
+		}
+		if l[:2] == "S:" {
+			if devlinks.Len() > 0 {
+				devlinks.WriteString(" ")
+			}
+			devlinks.WriteString("/dev/")
+			devlinks.WriteString(l[2:])
+			continue
+		}
+		if l[:2] != "E:" {
 			continue
 		}
 		kv := strings.SplitN(l[2:], "=", 2)
@@ -64,5 +77,9 @@ func (s *DiskIO) diskInfo(devName string) (map[string]string, error) {
 		di[kv[0]] = kv[1]
 	}
 
+	if devlinks.Len() > 0 {
+		di["DEVLINKS"] = devlinks.String()
+	}
+
 	return di, nil
 }

plugins/inputs/diskio/diskio_linux_test.go

@@ -14,6 +14,8 @@ import (
 var nullDiskInfo = []byte(`
 E:MY_PARAM_1=myval1
 E:MY_PARAM_2=myval2
+S:foo/bar/devlink
+S:foo/bar/devlink1
 `)
 
 // setupNullDisk sets up fake udev info as if /dev/null were a disk.
@@ -47,6 +49,7 @@ func TestDiskInfo(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "myval1", di["MY_PARAM_1"])
 	assert.Equal(t, "myval2", di["MY_PARAM_2"])
+	assert.Equal(t, "/dev/foo/bar/devlink /dev/foo/bar/devlink1", di["DEVLINKS"])
 
 	// test that data is cached
 	err = clean()
@@ -56,6 +59,7 @@ func TestDiskInfo(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "myval1", di["MY_PARAM_1"])
 	assert.Equal(t, "myval2", di["MY_PARAM_2"])
+	assert.Equal(t, "/dev/foo/bar/devlink /dev/foo/bar/devlink1", di["DEVLINKS"])
 
 	// unfortunately we can't adjust mtime on /dev/null to test cache invalidation
 }