pkg: new package cgroups

provide a package for managing cgroups.  This is not supposed to be a
complete implementation with all the features supported by cgroups,
but it is a minimal implementation designed around what libpod needs
and it is currently using.

For example, it is currently possible to Apply only the pids limit,
as it is used by libpod for stopping containers, any other Apply will
just fail.

The main goal here is to have a minimal library where we have full
control, so we can start playing with cgroup v2.

When the need arises, we can add more features.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 367 insertions, 0 deletions

diff --git a/pkg/cgroups/cgroups.go b/pkg/cgroups/cgroups.go
new file mode 100644
index 000000000..2a88c9db6
--- /dev/null
+++ b/pkg/cgroups/cgroups.go
@@ -0,0 +1,367 @@
+package cgroups
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+var (
+	// ErrCgroupDeleted means the cgroup was deleted
+	ErrCgroupDeleted = errors.New("cgroups: cgroup deleted")
+)
+
+// CgroupControl controls a cgroup hierarchy
+type CgroupControl struct {
+	cgroup2 bool
+	path    string
+	systemd bool
+	// List of additional cgroup subsystems joined that
+	// do not have a custom handler.
+	additionalControllers []controller
+}
+
+// CPUUsage keeps stats for the CPU usage
+type CPUUsage struct {
+	Kernel uint64
+	Total  uint64
+	PerCPU []uint64
+}
+
+// MemoryUsage keeps stats for the memory usage
+type MemoryUsage struct {
+	Usage uint64
+	Limit uint64
+}
+
+// CPUMetrics keeps stats for the CPU usage
+type CPUMetrics struct {
+	Usage CPUUsage
+}
+
+// BlkIOEntry describes an entry in the blkio stats
+type BlkIOEntry struct {
+	Op    string
+	Major uint64
+	Minor uint64
+	Value uint64
+}
+
+// BlkioMetrics keeps usage stats for the blkio cgroup controller
+type BlkioMetrics struct {
+	IoServiceBytesRecursive []BlkIOEntry
+}
+
+// MemoryMetrics keeps usage stats for the memory cgroup controller
+type MemoryMetrics struct {
+	Usage MemoryUsage
+}
+
+// PidsMetrics keeps usage stats for the pids cgroup controller
+type PidsMetrics struct {
+	Current uint64
+}
+
+// Metrics keeps usage stats for the cgroup controllers
+type Metrics struct {
+	CPU    CPUMetrics
+	Blkio  BlkioMetrics
+	Memory MemoryMetrics
+	Pids   PidsMetrics
+}
+
+type controller struct {
+	name    string
+	symlink bool
+}
+
+type controllerHandler interface {
+	Create(*CgroupControl) (bool, error)
+	Apply(*CgroupControl, *spec.LinuxResources) error
+	Destroy(*CgroupControl) error
+	Stat(*CgroupControl, *Metrics) error
+}
+
+const (
+	cgroupRoot         = "/sys/fs/cgroup"
+	_cgroup2SuperMagic = 0x63677270
+	// CPU is the cpu controller
+	CPU = "cpu"
+	// CPUAcct is the cpuacct controller
+	CPUAcct = "cpuacct"
+	// CPUset is the cpuset controller
+	CPUset = "cpuset"
+	// Memory is the memory controller
+	Memory = "memory"
+	// Pids is the pids controller
+	Pids = "pids"
+	// Blkio is the blkio controller
+	Blkio = "blkio"
+)
+
+var handlers map[string]controllerHandler
+
+func init() {
+	handlers = make(map[string]controllerHandler)
+	handlers[CPU] = getCPUHandler()
+	handlers[CPUset] = getCpusetHandler()
+	handlers[Memory] = getMemoryHandler()
+	handlers[Pids] = getPidsHandler()
+	handlers[Blkio] = getBlkioHandler()
+}
+
+// getAvailableControllers get the available controllers
+func getAvailableControllers(exclude map[string]controllerHandler, cgroup2 bool) ([]controller, error) {
+	if cgroup2 {
+		return nil, fmt.Errorf("function not implemented yet")
+	}
+
+	infos, err := ioutil.ReadDir(cgroupRoot)
+	if err != nil {
+		return nil, err
+	}
+	var controllers []controller
+	for _, i := range infos {
+		name := i.Name()
+		if _, found := exclude[name]; found {
+			continue
+		}
+		c := controller{
+			name:    name,
+			symlink: !i.IsDir(),
+		}
+		controllers = append(controllers, c)
+	}
+	return controllers, nil
+}
+
+// getCgroupv1Path is a helper function to get the cgroup v1 path
+func (c *CgroupControl) getCgroupv1Path(name string) string {
+	return filepath.Join(cgroupRoot, name, c.path)
+}
+
+// initialize initializes the specified hierarchy
+func (c *CgroupControl) initialize() (err error) {
+	createdSoFar := map[string]controllerHandler{}
+	defer func() {
+		if err != nil {
+			for name, ctr := range createdSoFar {
+				if err := ctr.Destroy(c); err != nil {
+					logrus.Warningf("error cleaning up controller %s for %s", name, c.path)
+				}
+			}
+		}
+	}()
+	for name, handler := range handlers {
+		created, err := handler.Create(c)
+		if err != nil {
+			return err
+		}
+		if created {
+			createdSoFar[name] = handler
+		}
+	}
+
+	if !c.cgroup2 {
+		// We won't need to do this for cgroup v2
+		for _, ctr := range c.additionalControllers {
+			if ctr.symlink {
+				continue
+			}
+			path := c.getCgroupv1Path(ctr.name)
+			if err := os.MkdirAll(path, 0755); err != nil {
+				return errors.Wrapf(err, "error creating cgroup path %s for %s", path, ctr.name)
+			}
+		}
+	}
+
+	return nil
+}
+
+func (c *CgroupControl) createCgroupDirectory(controller string) (bool, error) {
+	cPath := c.getCgroupv1Path(controller)
+	_, err := os.Stat(cPath)
+	if err == nil {
+		return false, nil
+	}
+
+	if !os.IsNotExist(err) {
+		return false, err
+	}
+
+	if err := os.MkdirAll(cPath, 0755); err != nil {
+		return false, errors.Wrapf(err, "error creating cgroup for %s", controller)
+	}
+	return true, nil
+}
+
+func readFileAsUint64(path string) (uint64, error) {
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.ParseUint(cleanString(string(data)), 10, 0)
+}
+
+func (c *CgroupControl) writePidToTasks(pid int, name string) error {
+	path := filepath.Join(c.getCgroupv1Path(name), "tasks")
+	payload := []byte(fmt.Sprintf("%d", pid))
+	return ioutil.WriteFile(path, payload, 0644)
+}
+
+// New creates a new cgroup control
+func New(path string, resources *spec.LinuxResources) (*CgroupControl, error) {
+	cgroup2, err := IsCgroup2UnifiedMode()
+	if err != nil {
+		return nil, err
+	}
+	control := &CgroupControl{
+		cgroup2: cgroup2,
+		path:    path,
+	}
+
+	if !cgroup2 {
+		controllers, err := getAvailableControllers(handlers, false)
+		if err != nil {
+			return nil, err
+		}
+		control.additionalControllers = controllers
+	}
+
+	if err := control.initialize(); err != nil {
+		return nil, err
+	}
+
+	return control, nil
+}
+
+// NewSystemd creates a new cgroup control
+func NewSystemd(path string) (*CgroupControl, error) {
+	cgroup2, err := IsCgroup2UnifiedMode()
+	if err != nil {
+		return nil, err
+	}
+	control := &CgroupControl{
+		cgroup2: cgroup2,
+		path:    path,
+		systemd: true,
+	}
+	return control, nil
+}
+
+// Load loads an existing cgroup control
+func Load(path string) (*CgroupControl, error) {
+	cgroup2, err := IsCgroup2UnifiedMode()
+	if err != nil {
+		return nil, err
+	}
+	control := &CgroupControl{
+		cgroup2: cgroup2,
+		path:    path,
+		systemd: false,
+	}
+	if !cgroup2 {
+		for name := range handlers {
+			p := control.getCgroupv1Path(name)
+			if _, err := os.Stat(p); err != nil {
+				if os.IsNotExist(err) {
+					// compatible with the error code
+					// used by containerd/cgroups
+					return nil, ErrCgroupDeleted
+				}
+			}
+		}
+	}
+	return control, nil
+}
+
+// CreateSystemdUnit creates the systemd cgroup
+func (c *CgroupControl) CreateSystemdUnit(path string) error {
+	if !c.systemd {
+		return fmt.Errorf("the cgroup controller is not using systemd")
+	}
+	return systemdCreate(path)
+}
+
+// Delete cleans a cgroup
+func (c *CgroupControl) Delete() error {
+	return c.DeleteByPath(c.path)
+}
+
+// DeleteByPath deletes the specified cgroup path
+func (c *CgroupControl) DeleteByPath(path string) error {
+	if c.systemd {
+		return systemdDestroy(path)
+	}
+	var lastError error
+	for _, h := range handlers {
+		if err := h.Destroy(c); err != nil {
+			lastError = err
+		}
+	}
+
+	for _, ctr := range c.additionalControllers {
+		if err := os.Remove(c.getCgroupv1Path(ctr.name)); err != nil {
+			lastError = err
+		}
+	}
+	return lastError
+}
+
+// Update updates the cgroups
+func (c *CgroupControl) Update(resources *spec.LinuxResources) error {
+	for _, h := range handlers {
+		if err := h.Apply(c, resources); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// AddPid moves the specified pid to the cgroup
+func (c *CgroupControl) AddPid(pid int) error {
+	if c.cgroup2 {
+		return fmt.Errorf("function not implemented yet")
+	}
+	pidString := []byte(fmt.Sprintf("%d\n", pid))
+
+	var names []string
+	for n := range handlers {
+		names = append(names, n)
+	}
+
+	for _, c := range c.additionalControllers {
+		if !c.symlink {
+			names = append(names, c.name)
+		}
+	}
+
+	for _, n := range names {
+		p := filepath.Join(c.getCgroupv1Path(n), "tasks")
+		if err := ioutil.WriteFile(p, pidString, 0644); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Stat returns usage statistics for the cgroup
+func (c *CgroupControl) Stat() (*Metrics, error) {
+	if c.cgroup2 {
+		return nil, fmt.Errorf("function not implemented yet")
+	}
+	m := Metrics{}
+	for _, h := range handlers {
+		if err := h.Stat(c, &m); err != nil {
+			return nil, err
+		}
+	}
+	return &m, nil
+}