Add pause and unpause commands to nsinit

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)

nsinit/main.go

@@ -32,6 +32,8 @@ func main() {
 		statsCommand,
 		configCommand,
 		nsenterCommand,
+		pauseCommand,
+		unpauseCommand,
 	}
 
 	if err := app.Run(os.Args); err != nil {

nsinit/pause.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"log"
+
+	"github.com/codegangsta/cli"
+	"github.com/docker/libcontainer/cgroups"
+	"github.com/docker/libcontainer/cgroups/fs"
+	"github.com/docker/libcontainer/cgroups/systemd"
+)
+
+var pauseCommand = cli.Command{
+	Name:   "pause",
+	Usage:  "pause the container's processes",
+	Action: pauseAction,
+}
+
+var unpauseCommand = cli.Command{
+	Name:   "unpause",
+	Usage:  "unpause the container's processes",
+	Action: unpauseAction,
+}
+
+func pauseAction(context *cli.Context) {
+	if err := toggle(cgroups.Frozen); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func unpauseAction(context *cli.Context) {
+	if err := toggle(cgroups.Thawed); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func toggle(state cgroups.FreezerState) error {
+	container, err := loadContainer()
+	if err != nil {
+		return err
+	}
+
+	if systemd.UseSystemd() {
+		err = systemd.Freeze(container.Cgroups, state)
+	} else {
+		err = fs.Freeze(container.Cgroups, state)
+	}
+
+	return err
+}