GoToSocial/vendor/github.com/containerd/cgroups/v2/manager.go

/*
   Copyright The containerd 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.
*/

package v2

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io/ioutil"
	"math"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/containerd/cgroups/v2/stats"

	systemdDbus "github.com/coreos/go-systemd/v22/dbus"
	"github.com/godbus/dbus/v5"
	"github.com/opencontainers/runtime-spec/specs-go"
	"github.com/sirupsen/logrus"
	"golang.org/x/sys/unix"
)

const (
	subtreeControl     = "cgroup.subtree_control"
	controllersFile    = "cgroup.controllers"
	defaultCgroup2Path = "/sys/fs/cgroup"
	defaultSlice       = "system.slice"
)

var (
	canDelegate bool
)

type Event struct {
	Low     uint64
	High    uint64
	Max     uint64
	OOM     uint64
	OOMKill uint64
}

// Resources for a cgroups v2 unified hierarchy
type Resources struct {
	CPU     *CPU
	Memory  *Memory
	Pids    *Pids
	IO      *IO
	RDMA    *RDMA
	HugeTlb *HugeTlb
	// When len(Devices) is zero, devices are not controlled
	Devices []specs.LinuxDeviceCgroup
}

// Values returns the raw filenames and values that
// can be written to the unified hierarchy
func (r *Resources) Values() (o []Value) {
	if r.CPU != nil {
		o = append(o, r.CPU.Values()...)
	}
	if r.Memory != nil {
		o = append(o, r.Memory.Values()...)
	}
	if r.Pids != nil {
		o = append(o, r.Pids.Values()...)
	}
	if r.IO != nil {
		o = append(o, r.IO.Values()...)
	}
	if r.RDMA != nil {
		o = append(o, r.RDMA.Values()...)
	}
	if r.HugeTlb != nil {
		o = append(o, r.HugeTlb.Values()...)
	}
	return o
}

// EnabledControllers returns the list of all not nil resource controllers
func (r *Resources) EnabledControllers() (c []string) {
	if r.CPU != nil {
		c = append(c, "cpu")
		c = append(c, "cpuset")
	}
	if r.Memory != nil {
		c = append(c, "memory")
	}
	if r.Pids != nil {
		c = append(c, "pids")
	}
	if r.IO != nil {
		c = append(c, "io")
	}
	if r.RDMA != nil {
		c = append(c, "rdma")
	}
	if r.HugeTlb != nil {
		c = append(c, "hugetlb")
	}
	return
}

// Value of a cgroup setting
type Value struct {
	filename string
	value    interface{}
}

// write the value to the full, absolute path, of a unified hierarchy
func (c *Value) write(path string, perm os.FileMode) error {
	var data []byte
	switch t := c.value.(type) {
	case uint64:
		data = []byte(strconv.FormatUint(t, 10))
	case uint16:
		data = []byte(strconv.FormatUint(uint64(t), 10))
	case int64:
		data = []byte(strconv.FormatInt(t, 10))
	case []byte:
		data = t
	case string:
		data = []byte(t)
	case CPUMax:
		data = []byte(t)
	default:
		return ErrInvalidFormat
	}

	// Retry writes on EINTR; see:
	//    https://github.com/golang/go/issues/38033
	for {
		err := ioutil.WriteFile(
			filepath.Join(path, c.filename),
			data,
			perm,
		)
		if err == nil {
			return nil
		} else if !errors.Is(err, syscall.EINTR) {
			return err
		}
	}
}

func writeValues(path string, values []Value) error {
	for _, o := range values {
		if err := o.write(path, defaultFilePerm); err != nil {
			return err
		}
	}
	return nil
}

func NewManager(mountpoint string, group string, resources *Resources) (*Manager, error) {
	if resources == nil {
		return nil, errors.New("resources reference is nil")
	}
	if err := VerifyGroupPath(group); err != nil {
		return nil, err
	}
	path := filepath.Join(mountpoint, group)
	if err := os.MkdirAll(path, defaultDirPerm); err != nil {
		return nil, err
	}
	m := Manager{
		unifiedMountpoint: mountpoint,
		path:              path,
	}
	if err := m.ToggleControllers(resources.EnabledControllers(), Enable); err != nil {
		// clean up cgroup dir on failure
		os.Remove(path)
		return nil, err
	}
	if err := setResources(path, resources); err != nil {
		os.Remove(path)
		return nil, err
	}
	return &m, nil
}

func LoadManager(mountpoint string, group string) (*Manager, error) {
	if err := VerifyGroupPath(group); err != nil {
		return nil, err
	}
	path := filepath.Join(mountpoint, group)
	return &Manager{
		unifiedMountpoint: mountpoint,
		path:              path,
	}, nil
}

type Manager struct {
	unifiedMountpoint string
	path              string
}

func setResources(path string, resources *Resources) error {
	if resources != nil {
		if err := writeValues(path, resources.Values()); err != nil {
			return err
		}
		if err := setDevices(path, resources.Devices); err != nil {
			return err
		}
	}
	return nil
}

func (c *Manager) RootControllers() ([]string, error) {
	b, err := ioutil.ReadFile(filepath.Join(c.unifiedMountpoint, controllersFile))
	if err != nil {
		return nil, err
	}
	return strings.Fields(string(b)), nil
}

func (c *Manager) Controllers() ([]string, error) {
	b, err := ioutil.ReadFile(filepath.Join(c.path, controllersFile))
	if err != nil {
		return nil, err
	}
	return strings.Fields(string(b)), nil
}

func (c *Manager) Update(resources *Resources) error {
	return setResources(c.path, resources)
}

type ControllerToggle int

const (
	Enable ControllerToggle = iota + 1
	Disable
)

func toggleFunc(controllers []string, prefix string) []string {
	out := make([]string, len(controllers))
	for i, c := range controllers {
		out[i] = prefix + c
	}
	return out
}

func (c *Manager) ToggleControllers(controllers []string, t ControllerToggle) error {
	// when c.path is like /foo/bar/baz, the following files need to be written:
	// * /sys/fs/cgroup/cgroup.subtree_control
	// * /sys/fs/cgroup/foo/cgroup.subtree_control
	// * /sys/fs/cgroup/foo/bar/cgroup.subtree_control
	// Note that /sys/fs/cgroup/foo/bar/baz/cgroup.subtree_control does not need to be written.
	split := strings.Split(c.path, "/")
	var lastErr error
	for i := range split {
		f := strings.Join(split[:i], "/")
		if !strings.HasPrefix(f, c.unifiedMountpoint) || f == c.path {
			continue
		}
		filePath := filepath.Join(f, subtreeControl)
		if err := c.writeSubtreeControl(filePath, controllers, t); err != nil {
			// When running as rootless, the user may face EPERM on parent groups, but it is neglible when the
			// controller is already written.
			// So we only return the last error.
			lastErr = fmt.Errorf("failed to write subtree controllers %+v to %q: %w", controllers, filePath, err)
		} else {
			lastErr = nil
		}
	}
	return lastErr
}

func (c *Manager) writeSubtreeControl(filePath string, controllers []string, t ControllerToggle) error {
	f, err := os.OpenFile(filePath, os.O_WRONLY, 0)
	if err != nil {
		return err
	}
	defer f.Close()
	switch t {
	case Enable:
		controllers = toggleFunc(controllers, "+")
	case Disable:
		controllers = toggleFunc(controllers, "-")
	}
	_, err = f.WriteString(strings.Join(controllers, " "))
	return err
}

func (c *Manager) NewChild(name string, resources *Resources) (*Manager, error) {
	if strings.HasPrefix(name, "/") {
		return nil, errors.New("name must be relative")
	}
	path := filepath.Join(c.path, name)
	if err := os.MkdirAll(path, defaultDirPerm); err != nil {
		return nil, err
	}
	m := Manager{
		unifiedMountpoint: c.unifiedMountpoint,
		path:              path,
	}
	if resources != nil {
		if err := m.ToggleControllers(resources.EnabledControllers(), Enable); err != nil {
			// clean up cgroup dir on failure
			os.Remove(path)
			return nil, err
		}
	}
	if err := setResources(path, resources); err != nil {
		// clean up cgroup dir on failure
		os.Remove(path)
		return nil, err
	}
	return &m, nil
}

func (c *Manager) AddProc(pid uint64) error {
	v := Value{
		filename: cgroupProcs,
		value:    pid,
	}
	return writeValues(c.path, []Value{v})
}

func (c *Manager) Delete() error {
	return remove(c.path)
}

func (c *Manager) Procs(recursive bool) ([]uint64, error) {
	var processes []uint64
	err := filepath.Walk(c.path, func(p string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if !recursive && info.IsDir() {
			if p == c.path {
				return nil
			}
			return filepath.SkipDir
		}
		_, name := filepath.Split(p)
		if name != cgroupProcs {
			return nil
		}
		procs, err := parseCgroupProcsFile(p)
		if err != nil {
			return err
		}
		processes = append(processes, procs...)
		return nil
	})
	return processes, err
}

var singleValueFiles = []string{
	"pids.current",
	"pids.max",
}

func (c *Manager) Stat() (*stats.Metrics, error) {
	controllers, err := c.Controllers()
	if err != nil {
		return nil, err
	}
	out := make(map[string]interface{})
	for _, controller := range controllers {
		switch controller {
		case "cpu", "memory":
			if err := readKVStatsFile(c.path, controller+".stat", out); err != nil {
				if os.IsNotExist(err) {
					continue
				}
				return nil, err
			}
		}
	}
	for _, name := range singleValueFiles {
		if err := readSingleFile(c.path, name, out); err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return nil, err
		}
	}
	memoryEvents := make(map[string]interface{})
	if err := readKVStatsFile(c.path, "memory.events", memoryEvents); err != nil {
		if !os.IsNotExist(err) {
			return nil, err
		}
	}
	var metrics stats.Metrics

	metrics.Pids = &stats.PidsStat{
		Current: getPidValue("pids.current", out),
		Limit:   getPidValue("pids.max", out),
	}
	metrics.CPU = &stats.CPUStat{
		UsageUsec:     getUint64Value("usage_usec", out),
		UserUsec:      getUint64Value("user_usec", out),
		SystemUsec:    getUint64Value("system_usec", out),
		NrPeriods:     getUint64Value("nr_periods", out),
		NrThrottled:   getUint64Value("nr_throttled", out),
		ThrottledUsec: getUint64Value("throttled_usec", out),
	}
	metrics.Memory = &stats.MemoryStat{
		Anon:                  getUint64Value("anon", out),
		File:                  getUint64Value("file", out),
		KernelStack:           getUint64Value("kernel_stack", out),
		Slab:                  getUint64Value("slab", out),
		Sock:                  getUint64Value("sock", out),
		Shmem:                 getUint64Value("shmem", out),
		FileMapped:            getUint64Value("file_mapped", out),
		FileDirty:             getUint64Value("file_dirty", out),
		FileWriteback:         getUint64Value("file_writeback", out),
		AnonThp:               getUint64Value("anon_thp", out),
		InactiveAnon:          getUint64Value("inactive_anon", out),
		ActiveAnon:            getUint64Value("active_anon", out),
		InactiveFile:          getUint64Value("inactive_file", out),
		ActiveFile:            getUint64Value("active_file", out),
		Unevictable:           getUint64Value("unevictable", out),
		SlabReclaimable:       getUint64Value("slab_reclaimable", out),
		SlabUnreclaimable:     getUint64Value("slab_unreclaimable", out),
		Pgfault:               getUint64Value("pgfault", out),
		Pgmajfault:            getUint64Value("pgmajfault", out),
		WorkingsetRefault:     getUint64Value("workingset_refault", out),
		WorkingsetActivate:    getUint64Value("workingset_activate", out),
		WorkingsetNodereclaim: getUint64Value("workingset_nodereclaim", out),
		Pgrefill:              getUint64Value("pgrefill", out),
		Pgscan:                getUint64Value("pgscan", out),
		Pgsteal:               getUint64Value("pgsteal", out),
		Pgactivate:            getUint64Value("pgactivate", out),
		Pgdeactivate:          getUint64Value("pgdeactivate", out),
		Pglazyfree:            getUint64Value("pglazyfree", out),
		Pglazyfreed:           getUint64Value("pglazyfreed", out),
		ThpFaultAlloc:         getUint64Value("thp_fault_alloc", out),
		ThpCollapseAlloc:      getUint64Value("thp_collapse_alloc", out),
		Usage:                 getStatFileContentUint64(filepath.Join(c.path, "memory.current")),
		UsageLimit:            getStatFileContentUint64(filepath.Join(c.path, "memory.max")),
		SwapUsage:             getStatFileContentUint64(filepath.Join(c.path, "memory.swap.current")),
		SwapLimit:             getStatFileContentUint64(filepath.Join(c.path, "memory.swap.max")),
	}
	if len(memoryEvents) > 0 {
		metrics.MemoryEvents = &stats.MemoryEvents{
			Low:     getUint64Value("low", memoryEvents),
			High:    getUint64Value("high", memoryEvents),
			Max:     getUint64Value("max", memoryEvents),
			Oom:     getUint64Value("oom", memoryEvents),
			OomKill: getUint64Value("oom_kill", memoryEvents),
		}
	}
	metrics.Io = &stats.IOStat{Usage: readIoStats(c.path)}
	metrics.Rdma = &stats.RdmaStat{
		Current: rdmaStats(filepath.Join(c.path, "rdma.current")),
		Limit:   rdmaStats(filepath.Join(c.path, "rdma.max")),
	}
	metrics.Hugetlb = readHugeTlbStats(c.path)

	return &metrics, nil
}

func getUint64Value(key string, out map[string]interface{}) uint64 {
	v, ok := out[key]
	if !ok {
		return 0
	}
	switch t := v.(type) {
	case uint64:
		return t
	}
	return 0
}

func getPidValue(key string, out map[string]interface{}) uint64 {
	v, ok := out[key]
	if !ok {
		return 0
	}
	switch t := v.(type) {
	case uint64:
		return t
	case string:
		if t == "max" {
			return math.MaxUint64
		}
	}
	return 0
}

func readSingleFile(path string, file string, out map[string]interface{}) error {
	f, err := os.Open(filepath.Join(path, file))
	if err != nil {
		return err
	}
	defer f.Close()
	data, err := ioutil.ReadAll(f)
	if err != nil {
		return err
	}
	s := strings.TrimSpace(string(data))
	v, err := parseUint(s, 10, 64)
	if err != nil {
		// if we cannot parse as a uint, parse as a string
		out[file] = s
		return nil
	}
	out[file] = v
	return nil
}

func readKVStatsFile(path string, file string, out map[string]interface{}) error {
	f, err := os.Open(filepath.Join(path, file))
	if err != nil {
		return err
	}
	defer f.Close()

	s := bufio.NewScanner(f)
	for s.Scan() {
		name, value, err := parseKV(s.Text())
		if err != nil {
			return fmt.Errorf("error while parsing %s (line=%q): %w", filepath.Join(path, file), s.Text(), err)
		}
		out[name] = value
	}
	return s.Err()
}

func (c *Manager) Freeze() error {
	return c.freeze(c.path, Frozen)
}

func (c *Manager) Thaw() error {
	return c.freeze(c.path, Thawed)
}

func (c *Manager) freeze(path string, state State) error {
	values := state.Values()
	for {
		if err := writeValues(path, values); err != nil {
			return err
		}
		current, err := fetchState(path)
		if err != nil {
			return err
		}
		if current == state {
			return nil
		}
		time.Sleep(1 * time.Millisecond)
	}
}

func (c *Manager) isCgroupEmpty() bool {
	// In case of any error we return true so that we exit and don't leak resources
	out := make(map[string]interface{})
	if err := readKVStatsFile(c.path, "cgroup.events", out); err != nil {
		return true
	}
	if v, ok := out["populated"]; ok {
		populated, ok := v.(uint64)
		if !ok {
			return true
		}
		return populated == 0
	}
	return true
}

// MemoryEventFD returns inotify file descriptor and 'memory.events' inotify watch descriptor
func (c *Manager) MemoryEventFD() (int, uint32, error) {
	fpath := filepath.Join(c.path, "memory.events")
	fd, err := syscall.InotifyInit()
	if err != nil {
		return 0, 0, errors.New("failed to create inotify fd")
	}
	wd, err := syscall.InotifyAddWatch(fd, fpath, unix.IN_MODIFY)
	if err != nil {
		syscall.Close(fd)
		return 0, 0, fmt.Errorf("failed to add inotify watch for %q: %w", fpath, err)
	}
	// monitor to detect process exit/cgroup deletion
	evpath := filepath.Join(c.path, "cgroup.events")
	if _, err = syscall.InotifyAddWatch(fd, evpath, unix.IN_MODIFY); err != nil {
		syscall.Close(fd)
		return 0, 0, fmt.Errorf("failed to add inotify watch for %q: %w", evpath, err)
	}

	return fd, uint32(wd), nil
}

func (c *Manager) EventChan() (<-chan Event, <-chan error) {
	ec := make(chan Event)
	errCh := make(chan error, 1)
	go c.waitForEvents(ec, errCh)

	return ec, errCh
}

func parseMemoryEvents(out map[string]interface{}) (Event, error) {
	e := Event{}
	if v, ok := out["high"]; ok {
		e.High, ok = v.(uint64)
		if !ok {
			return Event{}, fmt.Errorf("cannot convert high to uint64: %+v", v)
		}
	}
	if v, ok := out["low"]; ok {
		e.Low, ok = v.(uint64)
		if !ok {
			return Event{}, fmt.Errorf("cannot convert low to uint64: %+v", v)
		}
	}
	if v, ok := out["max"]; ok {
		e.Max, ok = v.(uint64)
		if !ok {
			return Event{}, fmt.Errorf("cannot convert max to uint64: %+v", v)
		}
	}
	if v, ok := out["oom"]; ok {
		e.OOM, ok = v.(uint64)
		if !ok {
			return Event{}, fmt.Errorf("cannot convert oom to uint64: %+v", v)
		}
	}
	if v, ok := out["oom_kill"]; ok {
		e.OOMKill, ok = v.(uint64)
		if !ok {
			return Event{}, fmt.Errorf("cannot convert oom_kill to uint64: %+v", v)
		}
	}
	return e, nil
}

func (c *Manager) waitForEvents(ec chan<- Event, errCh chan<- error) {
	defer close(errCh)

	fd, _, err := c.MemoryEventFD()
	if err != nil {
		errCh <- err
		return
	}
	defer syscall.Close(fd)

	for {
		buffer := make([]byte, syscall.SizeofInotifyEvent*10)
		bytesRead, err := syscall.Read(fd, buffer)
		if err != nil {
			errCh <- err
			return
		}
		if bytesRead >= syscall.SizeofInotifyEvent {
			out := make(map[string]interface{})
			if err := readKVStatsFile(c.path, "memory.events", out); err != nil {
				// When cgroup is deleted read may return -ENODEV instead of -ENOENT from open.
				if _, statErr := os.Lstat(filepath.Join(c.path, "memory.events")); !os.IsNotExist(statErr) {
					errCh <- err
				}
				return
			}
			e, err := parseMemoryEvents(out)
			if err != nil {
				errCh <- err
				return
			}
			ec <- e
			if c.isCgroupEmpty() {
				return
			}
		}
	}
}

func setDevices(path string, devices []specs.LinuxDeviceCgroup) error {
	if len(devices) == 0 {
		return nil
	}
	insts, license, err := DeviceFilter(devices)
	if err != nil {
		return err
	}
	dirFD, err := unix.Open(path, unix.O_DIRECTORY|unix.O_RDONLY|unix.O_CLOEXEC, 0600)
	if err != nil {
		return fmt.Errorf("cannot get dir FD for %s", path)
	}
	defer unix.Close(dirFD)
	if _, err := LoadAttachCgroupDeviceFilter(insts, license, dirFD); err != nil {
		if !canSkipEBPFError(devices) {
			return err
		}
	}
	return nil
}

// getSystemdFullPath returns the full systemd path when creating a systemd slice group.
// the reason this is necessary is because the "-" character has a special meaning in
// systemd slice. For example, when creating a slice called "my-group-112233.slice",
// systemd will create a hierarchy like this:
//      /sys/fs/cgroup/my.slice/my-group.slice/my-group-112233.slice
func getSystemdFullPath(slice, group string) string {
	return filepath.Join(defaultCgroup2Path, dashesToPath(slice), dashesToPath(group))
}

// dashesToPath converts a slice name with dashes to it's corresponding systemd filesystem path.
func dashesToPath(in string) string {
	path := ""
	if strings.HasSuffix(in, ".slice") && strings.Contains(in, "-") {
		parts := strings.Split(in, "-")
		for i := range parts {
			s := strings.Join(parts[0:i+1], "-")
			if !strings.HasSuffix(s, ".slice") {
				s += ".slice"
			}
			path = filepath.Join(path, s)
		}
	} else {
		path = filepath.Join(path, in)
	}
	return path
}

func NewSystemd(slice, group string, pid int, resources *Resources) (*Manager, error) {
	if slice == "" {
		slice = defaultSlice
	}
	ctx := context.TODO()
	path := getSystemdFullPath(slice, group)
	conn, err := systemdDbus.NewWithContext(ctx)
	if err != nil {
		return &Manager{}, err
	}
	defer conn.Close()

	properties := []systemdDbus.Property{
		systemdDbus.PropDescription("cgroup " + group),
		newSystemdProperty("DefaultDependencies", false),
		newSystemdProperty("MemoryAccounting", true),
		newSystemdProperty("CPUAccounting", true),
		newSystemdProperty("IOAccounting", true),
	}

	// if we create a slice, the parent is defined via a Wants=
	if strings.HasSuffix(group, ".slice") {
		properties = append(properties, systemdDbus.PropWants(defaultSlice))
	} else {
		// otherwise, we use Slice=
		properties = append(properties, systemdDbus.PropSlice(defaultSlice))
	}

	// only add pid if its valid, -1 is used w/ general slice creation.
	if pid != -1 {
		properties = append(properties, newSystemdProperty("PIDs", []uint32{uint32(pid)}))
	}

	if resources.Memory != nil && resources.Memory.Min != nil && *resources.Memory.Min != 0 {
		properties = append(properties,
			newSystemdProperty("MemoryMin", uint64(*resources.Memory.Min)))
	}

	if resources.Memory != nil && resources.Memory.Max != nil && *resources.Memory.Max != 0 {
		properties = append(properties,
			newSystemdProperty("MemoryMax", uint64(*resources.Memory.Max)))
	}

	if resources.CPU != nil && resources.CPU.Weight != nil && *resources.CPU.Weight != 0 {
		properties = append(properties,
			newSystemdProperty("CPUWeight", *resources.CPU.Weight))
	}

	if resources.CPU != nil && resources.CPU.Max != "" {
		quota, period := resources.CPU.Max.extractQuotaAndPeriod()
		// cpu.cfs_quota_us and cpu.cfs_period_us are controlled by systemd.
		// corresponds to USEC_INFINITY in systemd
		// if USEC_INFINITY is provided, CPUQuota is left unbound by systemd
		// always setting a property value ensures we can apply a quota and remove it later
		cpuQuotaPerSecUSec := uint64(math.MaxUint64)
		if quota > 0 {
			// systemd converts CPUQuotaPerSecUSec (microseconds per CPU second) to CPUQuota
			// (integer percentage of CPU) internally.  This means that if a fractional percent of
			// CPU is indicated by Resources.CpuQuota, we need to round up to the nearest
			// 10ms (1% of a second) such that child cgroups can set the cpu.cfs_quota_us they expect.
			cpuQuotaPerSecUSec = uint64(quota*1000000) / period
			if cpuQuotaPerSecUSec%10000 != 0 {
				cpuQuotaPerSecUSec = ((cpuQuotaPerSecUSec / 10000) + 1) * 10000
			}
		}
		properties = append(properties,
			newSystemdProperty("CPUQuotaPerSecUSec", cpuQuotaPerSecUSec))
	}

	// If we can delegate, we add the property back in
	if canDelegate {
		properties = append(properties, newSystemdProperty("Delegate", true))
	}

	if resources.Pids != nil && resources.Pids.Max > 0 {
		properties = append(properties,
			newSystemdProperty("TasksAccounting", true),
			newSystemdProperty("TasksMax", uint64(resources.Pids.Max)))
	}

	statusChan := make(chan string, 1)
	if _, err := conn.StartTransientUnitContext(ctx, group, "replace", properties, statusChan); err == nil {
		select {
		case <-statusChan:
		case <-time.After(time.Second):
			logrus.Warnf("Timed out while waiting for StartTransientUnit(%s) completion signal from dbus. Continuing...", group)
		}
	} else if !isUnitExists(err) {
		return &Manager{}, err
	}

	return &Manager{
		path: path,
	}, nil
}

func LoadSystemd(slice, group string) (*Manager, error) {
	if slice == "" {
		slice = defaultSlice
	}
	path := getSystemdFullPath(slice, group)
	return &Manager{
		path: path,
	}, nil
}

func (c *Manager) DeleteSystemd() error {
	ctx := context.TODO()
	conn, err := systemdDbus.NewWithContext(ctx)
	if err != nil {
		return err
	}
	defer conn.Close()
	group := systemdUnitFromPath(c.path)
	ch := make(chan string)
	_, err = conn.StopUnitContext(ctx, group, "replace", ch)
	if err != nil {
		return err
	}
	<-ch
	return nil
}

func newSystemdProperty(name string, units interface{}) systemdDbus.Property {
	return systemdDbus.Property{
		Name:  name,
		Value: dbus.MakeVariant(units),
	}
}