Add common Cgroup interface

This is part of cgroupv2 patch set. Here we add a Cgroup interface that
both v1 and v2 need to conform to, and port cgroupv1 to use that first.

Signed-off-by: Daniel Dao <dqminh89@gmail.com>

4 files changed, 83 insertions, 40 deletions

diff --git a/runsc/cgroup/cgroup.go b/runsc/cgroup/cgroup.go
index fdcaed4ea..0eb5821a9 100644
--- a/runsc/cgroup/cgroup.go
+++ b/runsc/cgroup/cgroup.go
@@ -19,6 +19,7 @@ package cgroup
 import (
 	"bufio"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -286,7 +287,19 @@ func loadPathsHelper(cgroup, mountinfo io.Reader) (map[string]string, error) {
 	return paths, nil
 }
 
-// Cgroup represents a group inside all controllers. For example:
+// Cgroup represents a cgroup configuration.
+type Cgroup interface {
+	Install(res *specs.LinuxResources) error
+	Uninstall() error
+	Join() (func(), error)
+	CPUQuota() (float64, error)
+	CPUUsage() (uint64, error)
+	NumCPU() (int, error)
+	MemoryLimit() (uint64, error)
+	MakePath(controllerName string) string
+}
+
+// cgroupV1 represents a group inside all controllers. For example:
 //   Name='/foo/bar' maps to /sys/fs/cgroup/<controller>/foo/bar on
 //   all controllers.
 //
@@ -294,7 +307,7 @@ func loadPathsHelper(cgroup, mountinfo io.Reader) (map[string]string, error) {
 // location. For example:
 //   Name='foo/bar' and Parent[ctrl]="/user.slice", then it will map to
 //   /sys/fs/cgroup/<ctrl>/user.slice/foo/bar
-type Cgroup struct {
+type cgroupV1 struct {
 	Name    string            `json:"name"`
 	Parents map[string]string `json:"parents"`
 	Own     map[string]bool   `json:"own"`
@@ -302,7 +315,7 @@ type Cgroup struct {
 
 // NewFromSpec creates a new Cgroup instance if the spec includes a cgroup path.
 // Returns nil otherwise. Cgroup paths are loaded based on the current process.
-func NewFromSpec(spec *specs.Spec) (*Cgroup, error) {
+func NewFromSpec(spec *specs.Spec) (Cgroup, error) {
 	if spec.Linux == nil || spec.Linux.CgroupsPath == "" {
 		return nil, nil
 	}
@@ -311,16 +324,16 @@ func NewFromSpec(spec *specs.Spec) (*Cgroup, error) {
 
 // NewFromPath creates a new Cgroup instance from the specified relative path.
 // Cgroup paths are loaded based on the current process.
-func NewFromPath(cgroupsPath string) (*Cgroup, error) {
+func NewFromPath(cgroupsPath string) (Cgroup, error) {
 	return new("self", cgroupsPath)
 }
 
 // NewFromPid loads cgroup for the given process.
-func NewFromPid(pid int) (*Cgroup, error) {
+func NewFromPid(pid int) (Cgroup, error) {
 	return new(strconv.Itoa(pid), "")
 }
 
-func new(pid, cgroupsPath string) (*Cgroup, error) {
+func new(pid, cgroupsPath string) (Cgroup, error) {
 	var parents map[string]string
 
 	// If path is relative, load cgroup paths for the process to build the
@@ -332,7 +345,7 @@ func new(pid, cgroupsPath string) (*Cgroup, error) {
 			return nil, fmt.Errorf("finding current cgroups: %w", err)
 		}
 	}
-	cg := &Cgroup{
+	cg := &cgroupV1{
 		Name:    cgroupsPath,
 		Parents: parents,
 		Own:     make(map[string]bool),
@@ -341,10 +354,39 @@ func new(pid, cgroupsPath string) (*Cgroup, error) {
 	return cg, nil
 }
 
+// CgroupJSON is a wrapper for Cgroup that can be encoded to JSON.
+type CgroupJSON struct {
+	Cgroup Cgroup `json:"cgroup"`
+}
+
+type cgroupJSONv1 struct {
+	Cgroup *cgroupV1 `json:"cgroup"`
+}
+
+// UnmarshalJSON implements json.Unmarshaler.UnmarshalJSON
+func (c *CgroupJSON) UnmarshalJSON(data []byte) error {
+	v1 := cgroupJSONv1{}
+	err := json.Unmarshal(data, &v1)
+	if v1.Cgroup != nil {
+		c.Cgroup = v1.Cgroup
+	}
+	return err
+}
+
+// MarshalJSON implements json.Marshaler.MarshalJSON
+func (c *CgroupJSON) MarshalJSON() ([]byte, error) {
+	if c.Cgroup == nil {
+		v1 := cgroupJSONv1{}
+		return json.Marshal(&v1)
+	}
+	v1 := cgroupJSONv1{Cgroup: c.Cgroup.(*cgroupV1)}
+	return json.Marshal(&v1)
+}
+
 // Install creates and configures cgroups according to 'res'. If cgroup path
 // already exists, it means that the caller has already provided a
 // pre-configured cgroups, and 'res' is ignored.
-func (c *Cgroup) Install(res *specs.LinuxResources) error {
+func (c *cgroupV1) Install(res *specs.LinuxResources) error {
 	log.Debugf("Installing cgroup path %q", c.Name)
 
 	// Clean up partially created cgroups on error. Errors during cleanup itself
@@ -369,7 +411,7 @@ func (c *Cgroup) Install(res *specs.LinuxResources) error {
 	for _, key := range missing {
 		ctrlr := controllers[key]
 
-		if skip, err := c.createController(key); skip && ctrlr.optional() {
+		if skip, err := createController(c, key); skip && ctrlr.optional() {
 			if err := ctrlr.skip(res); err != nil {
 				return err
 			}
@@ -394,7 +436,7 @@ func (c *Cgroup) Install(res *specs.LinuxResources) error {
 // controller is enabled in the system. It returns a boolean indicating whether
 // the controller should be skipped (e.g. controller is disabled). In case it
 // should be skipped, it also returns the error it got.
-func (c *Cgroup) createController(name string) (bool, error) {
+func createController(c Cgroup, name string) (bool, error) {
 	ctrlrPath := filepath.Join(cgroupRoot, name)
 	if _, err := os.Stat(ctrlrPath); err != nil {
 		return os.IsNotExist(err), err
@@ -410,7 +452,7 @@ func (c *Cgroup) createController(name string) (bool, error) {
 
 // Uninstall removes the settings done in Install(). If cgroup path already
 // existed when Install() was called, Uninstall is a noop.
-func (c *Cgroup) Uninstall() error {
+func (c *cgroupV1) Uninstall() error {
 	log.Debugf("Deleting cgroup %q", c.Name)
 	g, ctx := errgroup.WithContext(context.Background())
 	for key := range controllers {
@@ -447,7 +489,7 @@ func (c *Cgroup) Uninstall() error {
 
 // Join adds the current process to the all controllers. Returns function that
 // restores cgroup to the original state.
-func (c *Cgroup) Join() (func(), error) {
+func (c *cgroupV1) Join() (func(), error) {
 	// First save the current state so it can be restored.
 	paths, err := loadPaths("self")
 	if err != nil {
@@ -492,7 +534,7 @@ func (c *Cgroup) Join() (func(), error) {
 }
 
 // CPUQuota returns the CFS CPU quota.
-func (c *Cgroup) CPUQuota() (float64, error) {
+func (c *cgroupV1) CPUQuota() (float64, error) {
 	path := c.MakePath("cpu")
 	quota, err := getInt(path, "cpu.cfs_quota_us")
 	if err != nil {
@@ -509,7 +551,7 @@ func (c *Cgroup) CPUQuota() (float64, error) {
 }
 
 // CPUUsage returns the total CPU usage of the cgroup.
-func (c *Cgroup) CPUUsage() (uint64, error) {
+func (c *cgroupV1) CPUUsage() (uint64, error) {
 	path := c.MakePath("cpuacct")
 	usage, err := getValue(path, "cpuacct.usage")
 	if err != nil {
@@ -519,7 +561,7 @@ func (c *Cgroup) CPUUsage() (uint64, error) {
 }
 
 // NumCPU returns the number of CPUs configured in 'cpuset/cpuset.cpus'.
-func (c *Cgroup) NumCPU() (int, error) {
+func (c *cgroupV1) NumCPU() (int, error) {
 	path := c.MakePath("cpuset")
 	cpuset, err := getValue(path, "cpuset.cpus")
 	if err != nil {
@@ -529,7 +571,7 @@ func (c *Cgroup) NumCPU() (int, error) {
 }
 
 // MemoryLimit returns the memory limit.
-func (c *Cgroup) MemoryLimit() (uint64, error) {
+func (c *cgroupV1) MemoryLimit() (uint64, error) {
 	path := c.MakePath("memory")
 	limStr, err := getValue(path, "memory.limit_in_bytes")
 	if err != nil {
@@ -539,7 +581,7 @@ func (c *Cgroup) MemoryLimit() (uint64, error) {
 }
 
 // MakePath builds a path to the given controller.
-func (c *Cgroup) MakePath(controllerName string) string {
+func (c *cgroupV1) MakePath(controllerName string) string {
 	path := c.Name
 	if parent, ok := c.Parents[controllerName]; ok {
 		path = filepath.Join(parent, c.Name)
diff --git a/runsc/cgroup/cgroup_test.go b/runsc/cgroup/cgroup_test.go
index 0b6a5431b..1447078a0 100644
--- a/runsc/cgroup/cgroup_test.go
+++ b/runsc/cgroup/cgroup_test.go
@@ -59,7 +59,7 @@ var dindMountinfo = `
 `
 
 func TestUninstallEnoent(t *testing.T) {
-	c := Cgroup{
+	c := cgroupV1{
 		// Use a non-existent name.
 		Name: "runsc-test-uninstall-656e6f656e740a",
 		Own:  make(map[string]bool),
diff --git a/runsc/container/container.go b/runsc/container/container.go
index 77a0f7eba..bee37e1b3 100644
--- a/runsc/container/container.go
+++ b/runsc/container/container.go
@@ -123,7 +123,7 @@ type Container struct {
 	// Note that CompatCgroup is created only for compatibility with tools
 	// that expect container cgroups to exist. Setting limits here makes no change
 	// to the container in question.
-	CompatCgroup *cgroup.Cgroup `json:"compatCgroup"`
+	CompatCgroup cgroup.CgroupJSON `json:"compatCgroup"`
 
 	// Saver handles load from/save to the state file safely from multiple
 	// processes.
@@ -249,7 +249,7 @@ func New(conf *config.Config, args Args) (*Container, error) {
 		if err != nil {
 			return nil, err
 		}
-		c.CompatCgroup = subCgroup
+		c.CompatCgroup = cgroup.CgroupJSON{Cgroup: subCgroup}
 		if err := runInCgroup(parentCgroup, func() error {
 			ioFiles, specFile, err := c.createGoferProcess(args.Spec, conf, args.BundleDir, args.Attached)
 			if err != nil {
@@ -297,7 +297,7 @@ func New(conf *config.Config, args Args) (*Container, error) {
 		if err != nil {
 			return nil, err
 		}
-		c.CompatCgroup = subCgroup
+		c.CompatCgroup = cgroup.CgroupJSON{Cgroup: subCgroup}
 
 		// If the console control socket file is provided, then create a new
 		// pty master/slave pair and send the TTY to the sandbox process.
@@ -365,7 +365,7 @@ func (c *Container) Start(conf *config.Config) error {
 	} else {
 		// Join cgroup to start gofer process to ensure it's part of the cgroup from
 		// the start (and all their children processes).
-		if err := runInCgroup(c.Sandbox.Cgroup, func() error {
+		if err := runInCgroup(c.Sandbox.CgroupJSON.Cgroup, func() error {
 			// Create the gofer process.
 			goferFiles, mountsFile, err := c.createGoferProcess(c.Spec, conf, c.BundleDir, false)
 			if err != nil {
@@ -784,7 +784,7 @@ func (c *Container) saveLocked() error {
 // root containers), and waits for the container or sandbox and the gofer
 // to stop. If any of them doesn't stop before timeout, an error is returned.
 func (c *Container) stop() error {
-	var parentCgroup *cgroup.Cgroup
+	var parentCgroup cgroup.Cgroup
 
 	if c.Sandbox != nil {
 		log.Debugf("Destroying container, cid: %s", c.ID)
@@ -793,7 +793,7 @@ func (c *Container) stop() error {
 		}
 		// Only uninstall parentCgroup for sandbox stop.
 		if c.Sandbox.IsRootContainer(c.ID) {
-			parentCgroup = c.Sandbox.Cgroup
+			parentCgroup = c.Sandbox.CgroupJSON.Cgroup
 		}
 		// Only set sandbox to nil after it has been told to destroy the container.
 		c.Sandbox = nil
@@ -813,8 +813,8 @@ func (c *Container) stop() error {
 	}
 
 	// Delete container cgroup if any.
-	if c.CompatCgroup != nil {
-		if err := c.CompatCgroup.Uninstall(); err != nil {
+	if c.CompatCgroup.Cgroup != nil {
+		if err := c.CompatCgroup.Cgroup.Uninstall(); err != nil {
 			return err
 		}
 	}
@@ -1059,7 +1059,7 @@ func isRoot(spec *specs.Spec) bool {
 
 // runInCgroup executes fn inside the specified cgroup. If cg is nil, execute
 // it in the current context.
-func runInCgroup(cg *cgroup.Cgroup, fn func() error) error {
+func runInCgroup(cg cgroup.Cgroup, fn func() error) error {
 	if cg == nil {
 		return fn()
 	}
@@ -1222,8 +1222,8 @@ func (c *Container) populateStats(event *boot.EventOut) {
 // setupCgroupForRoot configures and returns cgroup for the sandbox and the
 // root container. If `cgroupParentAnnotation` is set, use that path as the
 // sandbox cgroup and use Spec.Linux.CgroupsPath as the root container cgroup.
-func (c *Container) setupCgroupForRoot(conf *config.Config, spec *specs.Spec) (*cgroup.Cgroup, *cgroup.Cgroup, error) {
-	var parentCgroup *cgroup.Cgroup
+func (c *Container) setupCgroupForRoot(conf *config.Config, spec *specs.Spec) (cgroup.Cgroup, cgroup.Cgroup, error) {
+	var parentCgroup cgroup.Cgroup
 	if parentPath, ok := spec.Annotations[cgroupParentAnnotation]; ok {
 		var err error
 		parentCgroup, err = cgroup.NewFromPath(parentPath)
@@ -1256,7 +1256,7 @@ func (c *Container) setupCgroupForRoot(conf *config.Config, spec *specs.Spec) (*
 // subcontainers run exclusively inside the sandbox, subcontainer cgroups on the
 // host have no effect on them. However, some tools (e.g. cAdvisor) uses cgroups
 // paths to discover new containers and report stats for them.
-func (c *Container) setupCgroupForSubcontainer(conf *config.Config, spec *specs.Spec) (*cgroup.Cgroup, error) {
+func (c *Container) setupCgroupForSubcontainer(conf *config.Config, spec *specs.Spec) (cgroup.Cgroup, error) {
 	if isRoot(spec) {
 		if _, ok := spec.Annotations[cgroupParentAnnotation]; !ok {
 			return nil, nil
@@ -1276,7 +1276,7 @@ func (c *Container) setupCgroupForSubcontainer(conf *config.Config, spec *specs.
 // For rootless, it's possible that cgroups operations fail, in this case the
 // error is suppressed and a nil cgroups instance is returned to indicate that
 // no cgroups was configured.
-func cgroupInstall(conf *config.Config, cg *cgroup.Cgroup, res *specs.LinuxResources) (*cgroup.Cgroup, error) {
+func cgroupInstall(conf *config.Config, cg cgroup.Cgroup, res *specs.LinuxResources) (cgroup.Cgroup, error) {
 	// TODO(gvisor.dev/issue/3481): Remove when cgroups v2 is supported.
 	if cgroup.IsOnlyV2() {
 		if conf.Rootless {
diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index 714919139..8f7022fa1 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -72,8 +72,9 @@ type Sandbox struct {
 	// GID is the group ID in the parent namespace that the sandbox is running as.
 	GID int `json:"gid"`
 
-	// Cgroup has the cgroup configuration for the sandbox.
-	Cgroup *cgroup.Cgroup `json:"cgroup"`
+	// CgroupJSON contains the cgroup configuration that the sandbox is part of
+	// and allow serialization of the configuration into json
+	CgroupJSON cgroup.CgroupJSON `json:"cgroup"`
 
 	// OriginalOOMScoreAdj stores the value of oom_score_adj when the sandbox
 	// started, before it may be modified.
@@ -124,7 +125,7 @@ type Args struct {
 	MountsFile *os.File
 
 	// Gcgroup is the cgroup that the sandbox is part of.
-	Cgroup *cgroup.Cgroup
+	Cgroup cgroup.Cgroup
 
 	// Attached indicates that the sandbox lifecycle is attached with the caller.
 	// If the caller exits, the sandbox should exit too.
@@ -134,7 +135,7 @@ type Args struct {
 // New creates the sandbox process. The caller must call Destroy() on the
 // sandbox.
 func New(conf *config.Config, args *Args) (*Sandbox, error) {
-	s := &Sandbox{ID: args.ID, Cgroup: args.Cgroup}
+	s := &Sandbox{ID: args.ID, CgroupJSON: cgroup.CgroupJSON{Cgroup: args.Cgroup}}
 	// The Cleanup object cleans up partially created sandboxes when an error
 	// occurs. Any errors occurring during cleanup itself are ignored.
 	c := cleanup.Make(func() {
@@ -328,7 +329,7 @@ func (s *Sandbox) Processes(cid string) ([]*control.Process, error) {
 }
 
 // NewCGroup returns the sandbox's Cgroup, or an error if it does not have one.
-func (s *Sandbox) NewCGroup() (*cgroup.Cgroup, error) {
+func (s *Sandbox) NewCGroup() (cgroup.Cgroup, error) {
 	return cgroup.NewFromPid(s.Pid)
 }
 
@@ -763,8 +764,8 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		return err
 	}
 
-	if s.Cgroup != nil {
-		cpuNum, err := s.Cgroup.NumCPU()
+	if s.CgroupJSON.Cgroup != nil {
+		cpuNum, err := s.CgroupJSON.Cgroup.NumCPU()
 		if err != nil {
 			return fmt.Errorf("getting cpu count from cgroups: %v", err)
 		}
@@ -774,7 +775,7 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 			// leaving two cores as reasonable default.
 			const minCPUs = 2
 
-			quota, err := s.Cgroup.CPUQuota()
+			quota, err := s.CgroupJSON.Cgroup.CPUQuota()
 			if err != nil {
 				return fmt.Errorf("getting cpu qouta from cgroups: %v", err)
 			}
@@ -790,7 +791,7 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		}
 		cmd.Args = append(cmd.Args, "--cpu-num", strconv.Itoa(cpuNum))
 
-		memLimit, err := s.Cgroup.MemoryLimit()
+		memLimit, err := s.CgroupJSON.Cgroup.MemoryLimit()
 		if err != nil {
 			return fmt.Errorf("getting memory limit from cgroups: %v", err)
 		}