Use golang.org/x/sys/unix instead of syscall in diskio (#3384)

(cherry picked from commit 9a06249)

plugins/inputs/system/disk.go

@@ -2,6 +2,7 @@ package system
 
 import (
 	"fmt"
+	"log"
 	"regexp"
 	"strings"
 
@@ -164,14 +165,13 @@ func (s *DiskIOStats) Gather(acc telegraf.Accumulator) error {
 var varRegex = regexp.MustCompile(`\$(?:\w+|\{\w+\})`)
 
 func (s *DiskIOStats) diskName(devName string) string {
-	di, err := s.diskInfo(devName)
-	if err != nil {
-		// discard error :-(
-		// We can't return error because it's non-fatal to the Gather().
-		// And we have no logger, so we can't log it.
+	if len(s.NameTemplates) == 0 {
 		return devName
 	}
-	if di == nil {
+
+	di, err := s.diskInfo(devName)
+	if err != nil {
+		log.Printf("W! Error gathering disk info: %s", err)
 		return devName
 	}
 
@@ -198,14 +198,13 @@ func (s *DiskIOStats) diskName(devName string) string {
 }
 
 func (s *DiskIOStats) diskTags(devName string) map[string]string {
-	di, err := s.diskInfo(devName)
-	if err != nil {
-		// discard error :-(
-		// We can't return error because it's non-fatal to the Gather().
-		// And we have no logger, so we can't log it.
+	if len(s.DeviceTags) == 0 {
 		return nil
 	}
-	if di == nil {
+
+	di, err := s.diskInfo(devName)
+	if err != nil {
+		log.Printf("W! Error gathering disk info: %s", err)
 		return nil
 	}
 

plugins/inputs/system/disk_linux.go

@@ -5,51 +5,53 @@ import (
 	"fmt"
 	"os"
 	"strings"
-	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 type diskInfoCache struct {
-	stat   syscall.Stat_t
-	values map[string]string
+	udevDataPath string
+	values       map[string]string
 }
 
 var udevPath = "/run/udev/data"
 
 func (s *DiskIOStats) diskInfo(devName string) (map[string]string, error) {
-	fi, err := os.Stat("/dev/" + devName)
+	var err error
+	var stat unix.Stat_t
+
+	path := "/dev/" + devName
+	err = unix.Stat(path, &stat)
 	if err != nil {
 		return nil, err
 	}
-	stat, ok := fi.Sys().(*syscall.Stat_t)
-	if !ok {
-		return nil, nil
-	}
 
 	if s.infoCache == nil {
 		s.infoCache = map[string]diskInfoCache{}
 	}
 	ic, ok := s.infoCache[devName]
 	if ok {
 		return ic.values, nil
-	} else {
-		ic = diskInfoCache{
-			stat:   *stat,
-			values: map[string]string{},
-		}
-		s.infoCache[devName] = ic
 	}
-	di := ic.values
 
 	major := stat.Rdev >> 8 & 0xff
 	minor := stat.Rdev & 0xff
+	udevDataPath := fmt.Sprintf("%s/b%d:%d", udevPath, major, minor)
+
+	di := map[string]string{}
 
-	f, err := os.Open(fmt.Sprintf("%s/b%d:%d", udevPath, major, minor))
+	s.infoCache[devName] = diskInfoCache{
+		udevDataPath: udevDataPath,
+		values:       di,
+	}
+
+	f, err := os.Open(udevDataPath)
 	if err != nil {
 		return nil, err
 	}
 	defer f.Close()
-	scnr := bufio.NewScanner(f)
 
+	scnr := bufio.NewScanner(f)
 	for scnr.Scan() {
 		l := scnr.Text()
 		if len(l) < 4 || l[:2] != "E:" {