client, ctr: allow specifying unmanaged rootfs dir

e.g. ctr run -t --rm --rootfs /tmp/busybox-rootfs foo /bin/sh
(--rm removes the container but does not remove rootfs dir, of course)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cmd/ctr/run.go

@@ -47,7 +47,7 @@ func withMounts(context *cli.Context) containerd.SpecOpts {
 var runCommand = cli.Command{
 	Name:      "run",
 	Usage:     "run a container",
-	ArgsUsage: "IMAGE CONTAINER [COMMAND] [ARG...]",
+	ArgsUsage: "Image|RootFS ID [COMMAND] [ARG...]",
 	Flags: append([]cli.Flag{
 		cli.BoolFlag{
 			Name:  "tty,t",

cmd/ctr/run_unix.go

@@ -18,6 +18,13 @@ import (
 	"github.com/urfave/cli"
 )
 
+func init() {
+	runCommand.Flags = append(runCommand.Flags, cli.BoolFlag{
+		Name:  "rootfs",
+		Usage: "Use custom rootfs that is not managed by containerd snapshotter.",
+	})
+}
+
 func handleConsoleResize(ctx gocontext.Context, task resizer, con console.Console) error {
 	// do an initial resize of the console
 	size, err := con.Size()
@@ -54,38 +61,50 @@ func setHostNetworking() containerd.SpecOpts {
 
 func newContainer(ctx gocontext.Context, client *containerd.Client, context *cli.Context) (containerd.Container, error) {
 	var (
-		err             error
-		checkpointIndex digest.Digest
-
 		ref  = context.Args().First()
 		id   = context.Args().Get(1)
 		args = context.Args()[2:]
-		tty          = context.Bool("tty")
-		labelStrings = context.StringSlice("label")
 	)
 
-	labels := labelArgs(labelStrings)
-
 	if raw := context.String("checkpoint"); raw != "" {
-		if checkpointIndex, err = digest.Parse(raw); err != nil {
+		checkpointIndex, err := digest.Parse(raw)
+		if err != nil {
 			return nil, err
 		}
+		if checkpointIndex != "" {
+			return client.NewContainer(ctx, id, containerd.WithCheckpoint(v1.Descriptor{
+				Digest: checkpointIndex,
+			}, id))
 		}
+	}
+
+	var (
+		opts  []containerd.SpecOpts
+		cOpts []containerd.NewContainerOpts
+	)
+	cOpts = append(cOpts, containerd.WithContainerLabels(labelArgs(context.StringSlice("label"))))
+	if context.Bool("rootfs") {
+		opts = append(opts, containerd.WithRootFSPath(ref, context.Bool("readonly")))
+	} else {
 		image, err := client.GetImage(ctx, ref)
 		if err != nil {
 			return nil, err
 		}
-
+		opts = append(opts, containerd.WithImageConfig(ctx, image))
-	if checkpointIndex == "" {
+		cOpts = append(cOpts, containerd.WithImage(image))
-		opts := []containerd.SpecOpts{
+		if context.Bool("readonly") {
-			containerd.WithImageConfig(ctx, image),
+			cOpts = append(cOpts, containerd.WithNewSnapshotView(id, image))
-			withEnv(context),
+		} else {
-			withMounts(context),
+			cOpts = append(cOpts, containerd.WithNewSnapshot(id, image))
 		}
+		cOpts = append(cOpts, containerd.WithSnapshotter(context.String("snapshotter")))
+	}
+
+	opts = append(opts, withEnv(context), withMounts(context))
 	if len(args) > 0 {
 		opts = append(opts, containerd.WithProcessArgs(args...))
 	}
-		if tty {
+	if context.Bool("tty") {
 		opts = append(opts, withTTY())
 	}
 	if context.Bool("net-host") {
@@ -95,25 +114,8 @@ func newContainer(ctx gocontext.Context, client *containerd.Client, context *cli
 	if err != nil {
 		return nil, err
 	}
-		var rootfs containerd.NewContainerOpts
+	cOpts = append([]containerd.NewContainerOpts{containerd.WithSpec(spec)}, cOpts...)
-		if context.Bool("readonly") {
+	return client.NewContainer(ctx, id, cOpts...)
-			rootfs = containerd.WithNewSnapshotView(id, image)
-		} else {
-			rootfs = containerd.WithNewSnapshot(id, image)
-		}
-
-		return client.NewContainer(ctx, id,
-			containerd.WithSpec(spec),
-			containerd.WithImage(image),
-			containerd.WithContainerLabels(labels),
-			containerd.WithSnapshotter(context.String("snapshotter")),
-			rootfs,
-		)
-	}
-
-	return client.NewContainer(ctx, id, containerd.WithCheckpoint(v1.Descriptor{
-		Digest: checkpointIndex,
-	}, id))
 }
 
 func newTask(ctx gocontext.Context, container containerd.Container, checkpoint digest.Digest, tty bool) (containerd.Task, error) {

spec_unix.go

@@ -30,6 +30,12 @@ const (
 	defaultRootfsPath = "rootfs"
 )
 
+var (
+	defaultEnv = []string{
+		"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+	}
+)
+
 func defaltCaps() []string {
 	return []string{
 		"CAP_CHOWN",
@@ -76,6 +82,7 @@ func createDefaultSpec() (*specs.Spec, error) {
 			Path: defaultRootfsPath,
 		},
 		Process: &specs.Process{
+			Env:             defaultEnv,
 			Cwd:             "/",
 			NoNewPrivileges: true,
 			User: specs.User{
@@ -220,10 +227,7 @@ func WithImageConfig(ctx context.Context, i Image) SpecOpts {
 		default:
 			return fmt.Errorf("unknown image config media type %s", ic.MediaType)
 		}
-		env := []string{
+		s.Process.Env = append(s.Process.Env, config.Env...)
-			"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
-		}
-		s.Process.Env = append(env, config.Env...)
 		var (
 			uid, gid uint32
 		)
@@ -262,6 +266,18 @@ func WithImageConfig(ctx context.Context, i Image) SpecOpts {
 	}
 }
 
+// WithRootFSPath specifies unmanaged rootfs path.
+func WithRootFSPath(path string, readonly bool) SpecOpts {
+	return func(s *specs.Spec) error {
+		s.Root = &specs.Root{
+			Path:     path,
+			Readonly: readonly,
+		}
+		// Entrypoint is not set here (it's up to caller)
+		return nil
+	}
+}
+
 // WithSpec sets the provided spec for a new container
 func WithSpec(spec *specs.Spec) NewContainerOpts {
 	return func(ctx context.Context, client *Client, c *containers.Container) error {