Bootable containers

cmd/mobynit/main.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"flag"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	_ "github.com/docker/docker/daemon/graphdriver/aufs"
+	_ "github.com/docker/docker/daemon/graphdriver/overlay2"
+	"github.com/docker/docker/layer"
+	"github.com/docker/docker/pkg/idtools"
+	"golang.org/x/sys/unix"
+)
+
+const (
+	LAYER_ROOT = "/docker"
+	PIVOT_PATH = "/mnt/sysroot"
+)
+
+var graphDriver string
+
+func init() {
+	flag.StringVar(&graphDriver, "storage-driver", "aufs", "Storage driver to use")
+	flag.StringVar(&graphDriver, "s", "aufs", "Storage driver to use")
+}
+
+func mountContainer(containerID string) string {
+	if err := unix.Mount("", "/", "", unix.MS_REMOUNT, ""); err != nil {
+		log.Fatal("error remounting root as read/write:", err)
+	}
+	defer unix.Mount("", "/", "", unix.MS_REMOUNT | unix.MS_RDONLY, "")
+
+	if err := os.MkdirAll("/dev/shm", os.ModePerm); err != nil {
+		log.Fatal("creating /dev/shm failed:", err)
+	}
+
+	if err := unix.Mount("shm", "/dev/shm", "tmpfs", 0, ""); err != nil {
+		log.Fatal("error mounting /dev/shm:", err)
+	}
+	defer unix.Unmount("/dev/shm", unix.MNT_DETACH)
+
+	ls, err := layer.NewStoreFromOptions(layer.StoreOptions{
+		StorePath:                 LAYER_ROOT,
+		MetadataStorePathTemplate: filepath.Join(LAYER_ROOT, "image", "%s", "layerdb"),
+		IDMappings:                &idtools.IDMappings{},
+		GraphDriver:               graphDriver,
+		Platform:                  "linux",
+	})
+	if err != nil {
+		log.Fatal("error loading layer store:", err)
+	}
+
+	rwlayer, err := ls.GetRWLayer(containerID)
+	if err != nil {
+		log.Fatal("error getting container layer:", err)
+	}
+
+	newRoot, err := rwlayer.Mount("")
+	if err != nil {
+		log.Fatal("error mounting container fs:", err)
+	}
+
+	if err := unix.Mount("", newRoot, "", unix.MS_REMOUNT, ""); err != nil {
+		log.Fatal("error remounting container as read/write:", err)
+	}
+	defer unix.Mount("", newRoot, "", unix.MS_REMOUNT | unix.MS_RDONLY, "")
+
+	if err := os.MkdirAll(filepath.Join(newRoot, PIVOT_PATH), os.ModePerm); err != nil {
+		log.Fatal("creating /mnt/sysroot failed:", err)
+	}
+
+	return newRoot
+}
+
+func main() {
+	flag.Parse()
+
+	rawID, err := ioutil.ReadFile("/current/container_id")
+	if err != nil {
+		log.Fatal("could not get container ID:", err)
+	}
+	containerID := strings.TrimSpace(string(rawID))
+
+	newRoot := mountContainer(containerID)
+
+	if err := syscall.PivotRoot(newRoot, filepath.Join(newRoot, PIVOT_PATH)); err != nil {
+		log.Fatal("error while pivoting root:", err)
+	}
+
+	if err := unix.Chdir("/"); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := syscall.Exec("/sbin/init", os.Args, os.Environ()); err != nil {
+		log.Fatal("error executing init:", err)
+	}
+}

daemon/create.go

@@ -138,7 +138,7 @@ func (daemon *Daemon) create(params types.ContainerCreateConfig, managed bool) (
 	container.HostConfig.StorageOpt = params.HostConfig.StorageOpt
 
 	// Set RWLayer for container after mount labels have been set
-	if err := daemon.setRWLayer(container); err != nil {
+	if err := daemon.setRWLayer(container, params.HostConfig.Runtime); err != nil {
 		return nil, err
 	}
 
@@ -234,7 +234,7 @@ func (daemon *Daemon) generateSecurityOpt(hostConfig *containertypes.HostConfig)
 	return nil, nil
 }
 
-func (daemon *Daemon) setRWLayer(container *container.Container) error {
+func (daemon *Daemon) setRWLayer(container *container.Container, runtime string) error {
 	var layerID layer.ChainID
 	if container.ImageID != "" {
 		img, err := daemon.stores[container.Platform].imageStore.Get(container.ImageID)
@@ -244,9 +244,14 @@ func (daemon *Daemon) setRWLayer(container *container.Container) error {
 		layerID = img.RootFS.ChainID()
 	}
 
+	initFunc := daemon.getLayerInit()
+	if  runtime == "bare" {
+		initFunc = nil
+	}
+
 	rwLayerOpts := &layer.CreateRWLayerOpts{
 		MountLabel: container.MountLabel,
-		InitFunc:   daemon.getLayerInit(),
+		InitFunc:   initFunc,
 		StorageOpt: container.HostConfig.StorageOpt,
 	}
 

daemon/create_unix.go

@@ -17,6 +17,9 @@ import (
 
 // createContainerPlatformSpecificSettings performs platform specific container create functionality
 func (daemon *Daemon) createContainerPlatformSpecificSettings(container *container.Container, config *containertypes.Config, hostConfig *containertypes.HostConfig) error {
+	if hostConfig.Runtime == "bare" {
+		return nil
+	}
 	if err := daemon.Mount(container); err != nil {
 		return err
 	}

daemon/daemon_unix.go

@@ -641,6 +641,7 @@ func verifyDaemonSettings(conf *config.Config) error {
 		conf.Runtimes = make(map[string]types.Runtime)
 	}
 	conf.Runtimes[config.StockRuntimeName] = types.Runtime{Path: DefaultRuntimeBinary}
+	conf.Runtimes["bare"] = types.Runtime{}
 
 	return nil
 }