Non systemd support with unittest (influxdata#8785)

plugins/inputs/diskio/diskio_linux.go

@@ -16,8 +16,6 @@ type diskInfoCache struct {
 	values       map[string]string
 }
 
-var udevPath = "/run/udev/data"
-
 func (d *DiskIO) diskInfo(devName string) (map[string]string, error) {
 	var err error
 	var stat unix.Stat_t
@@ -37,9 +35,33 @@ func (d *DiskIO) diskInfo(devName string) (map[string]string, error) {
 		return ic.values, nil
 	}
 
-	major := unix.Major(uint64(stat.Rdev))
-	minor := unix.Minor(uint64(stat.Rdev))
-	udevDataPath := fmt.Sprintf("%s/b%d:%d", udevPath, major, minor)
+	var udevDataPath string
+	if ok && len(ic.udevDataPath) > 0 {
+		// We can reuse the udev data path from a "previous" entry.
+		// This allows us to also "poison" it during test scenarios
+		udevDataPath = ic.udevDataPath
+	} else {
+		major := unix.Major(uint64(stat.Rdev))
+		minor := unix.Minor(uint64(stat.Rdev))
+		udevDataPath = fmt.Sprintf("/run/udev/data/b%d:%d", major, minor)
+
+		_, err := os.Stat(udevDataPath)
+		if err != nil {
+			// This path failed, try the fallback .udev style (non-systemd)
+			udevDataPath = fmt.Sprintf("/dev/.udev/db/block:%s", devName)
+			_, err := os.Stat(udevDataPath)
+			if err != nil {
+				// Giving up, cannot retrieve disk info
+				return nil, err
+			}
+		}
+	}
+	// Final open of the confirmed (or the previously detected/used) udev file
+	f, err := os.Open(udevDataPath)
+	defer f.Close()
+	if err != nil {
+		return nil, err
+	}
 
 	di := map[string]string{}
 
@@ -49,12 +71,6 @@ func (d *DiskIO) diskInfo(devName string) (map[string]string, error) {
 		values:       di,
 	}
 
-	f, err := os.Open(udevDataPath)
-	if err != nil {
-		return nil, err
-	}
-	defer f.Close()
-
 	scnr := bufio.NewScanner(f)
 	var devlinks bytes.Buffer
 	for scnr.Scan() {

plugins/inputs/diskio/diskio_linux_test.go

@@ -19,19 +19,31 @@ S:foo/bar/devlink1
 `)
 
 // setupNullDisk sets up fake udev info as if /dev/null were a disk.
-func setupNullDisk(t *testing.T) func() error {
-	td, err := ioutil.TempDir("", ".telegraf.TestDiskInfo")
+func setupNullDisk(t *testing.T, s *DiskIO, devName string) func() error {
+	td, err := ioutil.TempFile("", ".telegraf.DiskInfoTest")
 	require.NoError(t, err)
 
-	origUdevPath := udevPath
+	if s.infoCache == nil {
+		s.infoCache = make(map[string]diskInfoCache, 0)
+	}
+	ic, ok := s.infoCache[devName]
+	if !ok {
+		// No previous calls for the device were done, easy to poison the cache
+		s.infoCache[devName] = diskInfoCache{
+			modifiedAt:   0,
+			udevDataPath: td.Name(),
+			values:       map[string]string{},
+		}
+	}
+	origUdevPath := ic.udevDataPath
 
 	cleanFunc := func() error {
-		udevPath = origUdevPath
-		return os.RemoveAll(td)
+		ic.udevDataPath = origUdevPath
+		return os.Remove(td.Name())
 	}
 
-	udevPath = td
-	err = ioutil.WriteFile(td+"/b1:3", nullDiskInfo, 0644) // 1:3 is the 'null' device
+	ic.udevDataPath = td.Name()
+	_, err = td.Write(nullDiskInfo)
 	if err != nil {
 		cleanFunc()
 		t.Fatal(err)
@@ -41,10 +53,9 @@ func setupNullDisk(t *testing.T) func() error {
 }
 
 func TestDiskInfo(t *testing.T) {
-	clean := setupNullDisk(t)
-	defer clean()
-
 	s := &DiskIO{}
+	clean := setupNullDisk(t, s, "null")
+	defer clean()
 	di, err := s.diskInfo("null")
 	require.NoError(t, err)
 	assert.Equal(t, "myval1", di["MY_PARAM_1"])
@@ -67,8 +78,6 @@ func TestDiskInfo(t *testing.T) {
 // DiskIOStats.diskName isn't a linux specific function, but dependent
 // functions are a no-op on non-Linux.
 func TestDiskIOStats_diskName(t *testing.T) {
-	defer setupNullDisk(t)()
-
 	tests := []struct {
 		templates []string
 		expected  string
@@ -88,6 +97,7 @@ func TestDiskIOStats_diskName(t *testing.T) {
 		s := DiskIO{
 			NameTemplates: tc.templates,
 		}
+		defer setupNullDisk(t, &s, "null")()
 		name, _ := s.diskName("null")
 		assert.Equal(t, tc.expected, name, "Templates: %#v", tc.templates)
 	}
@@ -96,11 +106,10 @@ func TestDiskIOStats_diskName(t *testing.T) {
 // DiskIOStats.diskTags isn't a linux specific function, but dependent
 // functions are a no-op on non-Linux.
 func TestDiskIOStats_diskTags(t *testing.T) {
-	defer setupNullDisk(t)()
-
 	s := &DiskIO{
 		DeviceTags: []string{"MY_PARAM_2"},
 	}
+	defer setupNullDisk(t, s, "null")()
 	dt := s.diskTags("null")
 	assert.Equal(t, map[string]string{"MY_PARAM_2": "myval2"}, dt)
 }