func getDevices(r io.Reader) (map[deviceKey]string, error) {
	var (
		s       = bufio.NewScanner(r)
		devices = make(map[deviceKey]string)
	)
	for s.Scan() {
		fields := strings.Fields(s.Text())
		major, err := strconv.Atoi(fields[0])
		if err != nil {
			return nil, err
		}
		minor, err := strconv.Atoi(fields[1])
		if err != nil {
			return nil, err
		}
		key := deviceKey{
			major: uint64(major),
			minor: uint64(minor),
		}
		if _, ok := devices[key]; ok {
			continue
		}
		devices[key] = filepath.Join("/dev", fields[2])
	}
	return devices, s.Err()
}
getDevices makes a best effort attempt to read all the devices into a map
keyed by major and minor number. Since devices may be mapped multiple times,
we err on taking the first occurrence.
package cgroups
import (
	"bufio"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	v1 "github.com/containerd/cgroups/stats/v1"
	specs "github.com/opencontainers/runtime-spec/specs-go"
)
func NewBlkio(root string, options ...func(controller *blkioController)) *blkioController {
	ctrl := &blkioController{
		root:     filepath.Join(root, string(Blkio)),
		procRoot: "/proc",
	}
	for _, opt := range options {
		opt(ctrl)
	}
	return ctrl
}
func ProcRoot(path string) func(controller *blkioController) {
	return func(c *blkioController) {
		c.procRoot = path
	}
}
type blkioController struct {
	root     string
	procRoot string
}
func (b *blkioController) Name() Name {
	return Blkio
}
func (b *blkioController) Path(path string) string {
	return filepath.Join(b.root, path)
}
func (b *blkioController) Create(path string, resources *specs.LinuxResources) error {
	if err := os.MkdirAll(b.Path(path), defaultDirPerm); err != nil {
		return err
	}
	if resources.BlockIO == nil {
		return nil
	}
	for _, t := range createBlkioSettings(resources.BlockIO) {
		if t.value != nil {
			if err := retryingWriteFile(
				filepath.Join(b.Path(path), "blkio."+t.name),
				t.format(t.value),
				defaultFilePerm,
			); err != nil {
				return err
			}
		}
	}
	return nil
}
func (b *blkioController) Update(path string, resources *specs.LinuxResources) error {
	return b.Create(path, resources)
}
func (b *blkioController) Stat(path string, stats *v1.Metrics) error {
	stats.Blkio = &v1.BlkIOStat{}
	var settings []blkioStatSettings
	if _, err := os.Lstat(filepath.Join(b.Path(path), "blkio.io_serviced_recursive")); err == nil {
		settings = []blkioStatSettings{
			{
				name:  "sectors_recursive",
				entry: &stats.Blkio.SectorsRecursive,
			},
			{
				name:  "io_service_bytes_recursive",
				entry: &stats.Blkio.IoServiceBytesRecursive,
			},
			{
				name:  "io_serviced_recursive",
				entry: &stats.Blkio.IoServicedRecursive,
			},
			{
				name:  "io_queued_recursive",
				entry: &stats.Blkio.IoQueuedRecursive,
			},
			{
				name:  "io_service_time_recursive",
				entry: &stats.Blkio.IoServiceTimeRecursive,
			},
			{
				name:  "io_wait_time_recursive",
				entry: &stats.Blkio.IoWaitTimeRecursive,
			},
			{
				name:  "io_merged_recursive",
				entry: &stats.Blkio.IoMergedRecursive,
			},
			{
				name:  "time_recursive",
				entry: &stats.Blkio.IoTimeRecursive,
			},
		}
	}
	f, err := os.Open(filepath.Join(b.procRoot, "diskstats"))
	if err != nil {
		return err
	}
	defer f.Close()
	devices, err := getDevices(f)
	if err != nil {
		return err
	}
	var size int
	for _, t := range settings {
		if err := b.readEntry(devices, path, t.name, t.entry); err != nil {
			return err
		}
		size += len(*t.entry)
	}
	if size > 0 {
		return nil
	}
	settings = []blkioStatSettings{
		{
			name:  "throttle.io_serviced",
			entry: &stats.Blkio.IoServicedRecursive,
		},
		{
			name:  "throttle.io_service_bytes",
			entry: &stats.Blkio.IoServiceBytesRecursive,
		},
	}
	for _, t := range settings {
		if err := b.readEntry(devices, path, t.name, t.entry); err != nil {
			return err
		}
	}
	return nil
}
func (b *blkioController) readEntry(devices map[deviceKey]string, path, name string, entry *[]*v1.BlkIOEntry) error {
	f, err := os.Open(filepath.Join(b.Path(path), "blkio."+name))
	if err != nil {
		return err
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	for sc.Scan() {
		fields := strings.FieldsFunc(sc.Text(), splitBlkIOStatLine)
		if len(fields) < 3 {
			if len(fields) == 2 && fields[0] == "Total" {
				continue
			} else {
				return fmt.Errorf("invalid line found while parsing %s: %s", path, sc.Text())
			}
		}
		major, err := strconv.ParseUint(fields[0], 10, 64)
		if err != nil {
			return err
		}
		minor, err := strconv.ParseUint(fields[1], 10, 64)
		if err != nil {
			return err
		}
		op := ""
		valueField := 2
		if len(fields) == 4 {
			op = fields[2]
			valueField = 3
		}
		v, err := strconv.ParseUint(fields[valueField], 10, 64)
		if err != nil {
			return err
		}
		*entry = append(*entry, &v1.BlkIOEntry{
			Device: devices[deviceKey{major, minor}],
			Major:  major,
			Minor:  minor,
			Op:     op,
			Value:  v,
		})
	}
	return sc.Err()
}
func createBlkioSettings(blkio *specs.LinuxBlockIO) []blkioSettings {
	settings := []blkioSettings{}
	if blkio.Weight != nil {
		settings = append(settings,
			blkioSettings{
				name:   "weight",
				value:  blkio.Weight,
				format: uintf,
			})
	}
	if blkio.LeafWeight != nil {
		settings = append(settings,
			blkioSettings{
				name:   "leaf_weight",
				value:  blkio.LeafWeight,
				format: uintf,
			})
	}
	for _, wd := range blkio.WeightDevice {
		if wd.Weight != nil {
			settings = append(settings,
				blkioSettings{
					name:   "weight_device",
					value:  wd,
					format: weightdev,
				})
		}
		if wd.LeafWeight != nil {
			settings = append(settings,
				blkioSettings{
					name:   "leaf_weight_device",
					value:  wd,
					format: weightleafdev,
				})
		}
	}
	for _, t := range []struct {
		name string
		list []specs.LinuxThrottleDevice
	}{
		{
			name: "throttle.read_bps_device",
			list: blkio.ThrottleReadBpsDevice,
		},
		{
			name: "throttle.read_iops_device",
			list: blkio.ThrottleReadIOPSDevice,
		},
		{
			name: "throttle.write_bps_device",
			list: blkio.ThrottleWriteBpsDevice,
		},
		{
			name: "throttle.write_iops_device",
			list: blkio.ThrottleWriteIOPSDevice,
		},
	} {
		for _, td := range t.list {
			settings = append(settings, blkioSettings{
				name:   t.name,
				value:  td,
				format: throttleddev,
			})
		}
	}
	return settings
}
type blkioSettings struct {
	name   string
	value  interface{}
	format func(v interface{}) []byte
}
type blkioStatSettings struct {
	name  string
	entry *[]*v1.BlkIOEntry
}
func uintf(v interface{}) []byte {
	return []byte(strconv.FormatUint(uint64(*v.(*uint16)), 10))
}
func weightdev(v interface{}) []byte {
	wd := v.(specs.LinuxWeightDevice)
	return []byte(fmt.Sprintf("%d:%d %d", wd.Major, wd.Minor, *wd.Weight))
}
func weightleafdev(v interface{}) []byte {
	wd := v.(specs.LinuxWeightDevice)
	return []byte(fmt.Sprintf("%d:%d %d", wd.Major, wd.Minor, *wd.LeafWeight))
}
func throttleddev(v interface{}) []byte {
	td := v.(specs.LinuxThrottleDevice)
	return []byte(fmt.Sprintf("%d:%d %d", td.Major, td.Minor, td.Rate))
}
func splitBlkIOStatLine(r rune) bool {
	return r == ' ' || r == ':'
}
type deviceKey struct {
	major, minor uint64
}