nsinit: Add a flag to enable system support for cgroups

Signed-off-by: Mrunal Patel <mrunalp@gmail.com>

nsinit/exec.go

@@ -23,6 +23,7 @@ var execCommand = cli.Command{
 	Action: execAction,
 	Flags: append([]cli.Flag{
 		cli.BoolFlag{Name: "tty,t", Usage: "allocate a TTY to the container"},
+		cli.BoolFlag{Name: "systemd", Usage: "Use systemd for managing cgroups, if available"},
 		cli.StringFlag{Name: "id", Value: "nsinit", Usage: "specify the ID for a container"},
 		cli.StringFlag{Name: "config", Value: "", Usage: "path to the configuration file"},
 		cli.StringFlag{Name: "user,u", Value: "root", Usage: "set the user, uid, and/or gid for the process"},

nsinit/utils.go

@@ -3,10 +3,12 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	log "github.com/Sirupsen/logrus"
 	"os"
 
 	"github.com/codegangsta/cli"
 	"github.com/docker/libcontainer"
+	"github.com/docker/libcontainer/cgroups/systemd"
 	"github.com/docker/libcontainer/configs"
 )
 
@@ -29,7 +31,15 @@ func loadConfig(context *cli.Context) (*configs.Config, error) {
 }
 
 func loadFactory(context *cli.Context) (libcontainer.Factory, error) {
-	return libcontainer.New(context.GlobalString("root"), libcontainer.Cgroupfs)
+	cgm := libcontainer.Cgroupfs
+	if context.Bool("systemd") {
+		if systemd.UseSystemd() {
+			cgm = libcontainer.SystemdCgroups
+		} else {
+			log.Warn("systemd cgroup flag passed, but systemd support for managing cgroups is not available.")
+		}
+	}
+	return libcontainer.New(context.GlobalString("root"), cgm)
 }
 
 func getContainer(context *cli.Context) (libcontainer.Container, error) {