Add a standalone test utility for cgroup package.

Although it has some overlap with nsinit utility, it is useful to test
cgroup functinality directly and try out new or internal features not
exposed through nsinit.

It still needs some work as I haven't added enough systemd support yet.
I also need to expose an enter method.

Docker-DCO-1.1-Signed-off-by: Rohit Jnagal <jnagal@google.com> (github: rjnagal)

cgroups/cgutil/cgutil.go

@@ -0,0 +1,265 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"os"
+	"syscall"
+	"time"
+
+	"github.com/codegangsta/cli"
+	"github.com/docker/libcontainer/cgroups"
+	"github.com/docker/libcontainer/cgroups/fs"
+	"github.com/docker/libcontainer/cgroups/systemd"
+)
+
+var createCommand = cli.Command{
+	Name:  "create",
+	Usage: "Create a cgroup container using the supplied configuration and initial process.",
+	Flags: []cli.Flag{
+		cli.StringFlag{"config, c", "cgroup.json", "path to container configuration"},
+		cli.IntFlag{"pid, p", 0, "pid of the initial process in the container"},
+	},
+	Action: createAction,
+}
+
+var destroyCommand = cli.Command{
+	Name:  "destroy",
+	Usage: "Destroy an existing cgroup container.",
+	Flags: []cli.Flag{
+		cli.StringFlag{"name, n", "", "container name"},
+		cli.StringFlag{"parent, p", "", "container parent"},
+	},
+	Action: destroyAction,
+}
+
+var statsCommand = cli.Command{
+	Name:  "stats",
+	Usage: "Get stats for cgroup",
+	Flags: []cli.Flag{
+		cli.StringFlag{"name, n", "", "container name"},
+		cli.StringFlag{"parent, p", "", "container parent"},
+	},
+	Action: statsAction,
+}
+
+var pauseCommand = cli.Command{
+	Name:  "pause",
+	Usage: "Pause cgroup",
+	Flags: []cli.Flag{
+		cli.StringFlag{"name, n", "", "container name"},
+		cli.StringFlag{"parent, p", "", "container parent"},
+	},
+	Action: pauseAction,
+}
+
+var resumeCommand = cli.Command{
+	Name:  "resume",
+	Usage: "Resume a paused cgroup",
+	Flags: []cli.Flag{
+		cli.StringFlag{"name, n", "", "container name"},
+		cli.StringFlag{"parent, p", "", "container parent"},
+	},
+	Action: resumeAction,
+}
+
+var psCommand = cli.Command{
+	Name:  "ps",
+	Usage: "Get list of pids for a cgroup",
+	Flags: []cli.Flag{
+		cli.StringFlag{"name, n", "", "container name"},
+		cli.StringFlag{"parent, p", "", "container parent"},
+	},
+	Action: psAction,
+}
+
+func loadConfig(c *cli.Context) (*cgroups.Cgroup, error) {
+	f, err := os.Open(c.String("config"))
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var config *cgroups.Cgroup
+	if err := json.NewDecoder(f).Decode(&config); err != nil {
+		log.Fatal(err)
+	}
+	return config, nil
+}
+
+func openLog(name string) error {
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0755)
+	if err != nil {
+		return err
+	}
+
+	log.SetOutput(f)
+	return nil
+}
+
+func getConfig(context *cli.Context) (*cgroups.Cgroup, error) {
+	name := context.String("name")
+	if name == "" {
+		log.Fatal(fmt.Errorf("Missing container name"))
+	}
+	parent := context.String("parent")
+	return &cgroups.Cgroup{
+		Name:   name,
+		Parent: parent,
+	}, nil
+}
+
+func killAll(config *cgroups.Cgroup) {
+	// We could use freezer here to prevent process spawning while we are trying
+	// to kill everything. But going with more portable solution of retrying for
+	// now.
+	pids := getPids(config)
+	killPids(pids)
+	retry := 10
+	for len(pids) != 0 || retry > 0 {
+		killPids(pids)
+		time.Sleep(100 * time.Millisecond)
+		retry--
+		pids = getPids(config)
+	}
+	if len(pids) != 0 {
+		log.Fatal(fmt.Errorf("Could not kill existing processes in the container."))
+	}
+}
+
+func getPids(config *cgroups.Cgroup) []int {
+	pids, err := fs.GetPids(config)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return pids
+}
+
+func killPids(pids []int) {
+	for _, pid := range pids {
+		// pids might go away on their own. Ignore errors.
+		syscall.Kill(pid, syscall.SIGKILL)
+	}
+}
+
+func setFreezerState(context *cli.Context, state cgroups.FreezerState) {
+	config, err := getConfig(context)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if systemd.UseSystemd() {
+		err = systemd.Freeze(config, state)
+	} else {
+		err = fs.Freeze(config, state)
+	}
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func createAction(context *cli.Context) {
+	config, err := loadConfig(context)
+	if err != nil {
+		log.Fatal(err)
+	}
+	pid := context.Int("pid")
+	if pid <= 0 {
+		log.Fatal(fmt.Errorf("Invalid pid : %d", pid))
+	}
+	if systemd.UseSystemd() {
+		_, err := systemd.Apply(config, pid)
+		if err != nil {
+			log.Fatal(err)
+		}
+	} else {
+		_, err := fs.Apply(config, pid)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func destroyAction(context *cli.Context) {
+	config, err := getConfig(context)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	killAll(config)
+	// Systemd will clean up cgroup state for empty container.
+	if !systemd.UseSystemd() {
+		err := fs.Cleanup(config)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func statsAction(context *cli.Context) {
+	config, err := getConfig(context)
+	if err != nil {
+		log.Fatal(err)
+	}
+	stats, err := fs.GetStats(config)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	out, err := json.MarshalIndent(stats, "", "\t")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("Usage stats for '%s':\n %v\n", config.Name, string(out))
+}
+
+func pauseAction(context *cli.Context) {
+	setFreezerState(context, cgroups.Frozen)
+}
+
+func resumeAction(context *cli.Context) {
+	setFreezerState(context, cgroups.Thawed)
+}
+
+func psAction(context *cli.Context) {
+	config, err := getConfig(context)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	pids, err := fs.GetPids(config)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Pids in '%s':\n", config.Name)
+	fmt.Println(pids)
+}
+
+func main() {
+	logPath := os.Getenv("log")
+	if logPath != "" {
+		if err := openLog(logPath); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	app := cli.NewApp()
+	app.Name = "cgutil"
+	app.Usage = "Test utility for libcontainer cgroups package"
+	app.Version = "0.1"
+
+	app.Commands = []cli.Command{
+		createCommand,
+		destroyCommand,
+		statsCommand,
+		pauseCommand,
+		resumeCommand,
+		psCommand,
+	}
+
+	if err := app.Run(os.Args); err != nil {
+		log.Fatal(err)
+	}
+}

cgroups/cgutil/sample_cgroup.json

@@ -0,0 +1,10 @@
+{
+	"name": "luke",
+	"parent": "darth",
+	"allow_all_devices": true,
+	"memory": 1073741824,
+	"memory_swap": -1,
+	"cpu_shares": 2048,
+	"cpu_quota": 500000,
+	"cpu_period": 250000
+}