Refactor the Sandbox package into Sandbox + Container.

This is a necessary prerequisite for supporting multiple containers in a single
sandbox.

All the commands (in cmd package) now call operations on Containers (container
package). When a Container first starts, it will create a Sandbox with the same
ID.

The Sandbox class is now simpler, as it only knows how to create boot/gofer
processes, and how to forward commands into the running boot process.

There are TODOs sprinkled around for additional support for multiple
containers. Most notably, we need to detect when a container is intended to run
in an existing sandbox (by reading the metadata), and then have some way to
signal to the sandbox to start a new container. Other urpc calls into the
sandbox need to pass the container ID, so the sandbox can run the operation on
the given container. These are only half-plummed through right now.

PiperOrigin-RevId: 196688269
Change-Id: I1ecf4abbb9dd8987a53ae509df19341aaf42b5b0

1 files changed, 94 insertions, 336 deletions

diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index 34bd6ea67..5dfa4cf0b 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -16,13 +16,9 @@
 package sandbox
 
 import (
-	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/exec"
-	"path/filepath"
-	"regexp"
 	"strconv"
 	"syscall"
 	"time"
@@ -38,308 +34,110 @@ import (
 	"gvisor.googlesource.com/gvisor/runsc/specutils"
 )
 
-// metadataFilename is the name of the metadata file relative to sandboxRoot
-// that holds sandbox metadata.
-const metadataFilename = "meta.json"
-
-// See libcontainer/factory_linux.go
-var idRegex = regexp.MustCompile(`^[\w+-\.]+$`)
-
-// validateID validates the sandbox id.
-func validateID(id string) error {
-	if !idRegex.MatchString(id) {
-		return fmt.Errorf("invalid sandbox id: %v", id)
-	}
-	return nil
-}
-
-func validateSpec(spec *specs.Spec) error {
-	if spec.Process.SelinuxLabel != "" {
-		return fmt.Errorf("SELinux is not supported: %s", spec.Process.SelinuxLabel)
-	}
-
-	// Docker uses AppArmor by default, so just log that it's being ignored.
-	if spec.Process.ApparmorProfile != "" {
-		log.Warningf("AppArmor profile %q is being ignored", spec.Process.ApparmorProfile)
-	}
-	// TODO: Apply seccomp to application inside sandbox.
-	if spec.Linux != nil && spec.Linux.Seccomp != nil {
-		log.Warningf("Seccomp spec is being ignored")
-	}
-	return nil
-}
-
-// Sandbox wraps a child sandbox process, and is responsible for saving and
-// loading sandbox metadata to disk.
-//
-// Within a root directory, we maintain subdirectories for each sandbox named
-// with the sandbox id.  The sandbox metadata is is stored as json within the
-// sandbox directory in a file named "meta.json".  This metadata format is
-// defined by us, and is not part of the OCI spec.
-//
-// Sandboxes must write this metadata file after any change to their internal
-// state.  The entire sandbox directory is deleted when the sandbox is
-// destroyed.
+// Sandbox wraps a sandbox process.
 //
-// TODO: Protect against concurrent changes to the sandbox metadata
-// file.
+// It is used to start/stop sandbox process (and associated processes like
+// gofers), as well as for running and manipulating containers inside a running
+// sandbox.
 type Sandbox struct {
-	// ID is the sandbox ID.
+	// ID is the id of the sandbox. By convention, this is the same ID as
+	// the first container run in the sandbox.
 	ID string `json:"id"`
 
-	// Spec is the OCI runtime spec that configures this sandbox.
-	Spec *specs.Spec `json:"spec"`
-
-	// BundleDir is the directory containing the sandbox bundle.
-	BundleDir string `json:"bundleDir"`
-
-	// SandboxRoot is the directory containing the sandbox metadata file.
-	SandboxRoot string `json:"sandboxRoot"`
-
-	// CreatedAt is the time the sandbox was created.
-	CreatedAt time.Time `json:"createdAt"`
-
-	// Owner is the sandbox owner.
-	Owner string `json:"owner"`
-
-	// ConsoleSocket is the path to a unix domain socket that will receive
-	// the console FD.  It is only used during create, so we don't need to
-	// store it in the metadata.
-	ConsoleSocket string `json:"-"`
-
-	// Pid is the pid of the running sandbox.  Only valid if Status is
-	// Created or Running.
+	// Pid is the pid of the running sandbox. May be 0 is the sandbox is
+	// not running.
 	Pid int `json:"pid"`
 
-	// GoferPid is the pid of the gofer running along side the sandbox. May be 0
-	// if the gofer has been killed or it's not being used.
+	// GoferPid is the pid of the gofer running along side the sandbox. May
+	// be 0 if the gofer has been killed or it's not being used.
 	GoferPid int `json:"goferPid"`
-
-	// Status is the current sandbox Status.
-	Status Status `json:"status"`
 }
 
-// Create creates the sandbox subprocess and writes the metadata file.  Args
-// are additional arguments that will be passed to the sandbox process.
-func Create(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, pidFile string, args []string) (*Sandbox, error) {
-	log.Debugf("Create sandbox %q in root dir: %s", id, conf.RootDir)
-	if err := validateID(id); err != nil {
-		return nil, err
-	}
-	if err := validateSpec(spec); err != nil {
-		return nil, err
-	}
-
-	sandboxRoot := filepath.Join(conf.RootDir, id)
-	if exists(sandboxRoot) {
-		return nil, fmt.Errorf("sandbox with id %q already exists: %q ", id, sandboxRoot)
-	}
+// Create creates the sandbox process.
+func Create(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket string) (*Sandbox, error) {
+	s := &Sandbox{ID: id}
 
-	s := &Sandbox{
-		ID:            id,
-		Spec:          spec,
-		ConsoleSocket: consoleSocket,
-		BundleDir:     bundleDir,
-		SandboxRoot:   sandboxRoot,
-		Status:        Creating,
-		Owner:         os.Getenv("USER"),
-	}
-
-	// Create sandbox process. If anything errors between now and the end of this
-	// function, we MUST clean up all sandbox resources.
-	if err := s.createProcesses(conf, args); err != nil {
-		s.Destroy()
+	binPath, err := specutils.BinPath()
+	if err != nil {
 		return nil, err
 	}
 
-	// Wait for the control server to come up (or timeout).  The sandbox is
-	// not "created" until that happens.
-	if err := s.waitForCreated(10 * time.Second); err != nil {
-		s.Destroy()
+	// Create the gofer process.
+	ioFiles, err := s.createGoferProcess(spec, conf, bundleDir, binPath)
+	if err != nil {
 		return nil, err
 	}
 
-	s.Status = Created
-	s.CreatedAt = time.Now()
-
-	// Save the metadata file.
-	if err := s.save(); err != nil {
-		s.Destroy()
+	// Create the sandbox process.
+	if err := s.createSandboxProcess(spec, conf, bundleDir, consoleSocket, binPath, ioFiles); err != nil {
 		return nil, err
 	}
 
-	// Write the pid file.  Containerd consideres the create complete after
-	// this file is created, so it must be the last thing we do.
-	if pidFile != "" {
-		if err := ioutil.WriteFile(pidFile, []byte(strconv.Itoa(s.Pid)), 0644); err != nil {
-			s.Destroy()
-			return nil, fmt.Errorf("error writing pid file: %v", err)
-		}
-	}
-
-	return s, nil
-}
-
-// Run is a helper that calls Create + Start + Wait.
-func Run(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, pidFile string, args []string) (syscall.WaitStatus, error) {
-	s, err := Create(id, spec, conf, bundleDir, consoleSocket, pidFile, args)
-	if err != nil {
-		return 0, fmt.Errorf("error creating sandbox: %v", err)
-	}
-	if err := s.Start(conf); err != nil {
-		return 0, fmt.Errorf("error starting sandbox: %v", err)
-	}
-	return s.Wait()
-}
-
-// Load loads a sandbox from with the given id from a metadata file.
-func Load(rootDir, id string) (*Sandbox, error) {
-	log.Debugf("Load sandbox %q %q", rootDir, id)
-	if err := validateID(id); err != nil {
+	// Wait for the control server to come up (or timeout).
+	if err := s.waitForCreated(10 * time.Second); err != nil {
 		return nil, err
 	}
-	sandboxRoot := filepath.Join(rootDir, id)
-	if !exists(sandboxRoot) {
-		return nil, fmt.Errorf("sandbox with id %q does not exist", id)
-	}
-	metaFile := filepath.Join(sandboxRoot, metadataFilename)
-	if !exists(metaFile) {
-		return nil, fmt.Errorf("sandbox with id %q does not have metadata file %q", id, metaFile)
-	}
-	metaBytes, err := ioutil.ReadFile(metaFile)
-	if err != nil {
-		return nil, fmt.Errorf("error reading sandbox metadata file %q: %v", metaFile, err)
-	}
-	var s Sandbox
-	if err := json.Unmarshal(metaBytes, &s); err != nil {
-		return nil, fmt.Errorf("error unmarshaling sandbox metadata from %q: %v", metaFile, err)
-	}
-
-	// If the status is "Running" or "Created", check that the process
-	// still exists, and set it to Stopped if it does not.
-	//
-	// This is inherently racey.
-	if s.Status == Running || s.Status == Created {
-		// Send signal 0 to check if process exists.
-		if err := s.Signal(0); err != nil {
-			// Process no longer exists.
-			s.Status = Stopped
-			s.Pid = 0
-		}
-	}
 
-	return &s, nil
-}
-
-// List returns all sandbox ids in the given root directory.
-func List(rootDir string) ([]string, error) {
-	log.Debugf("List sandboxes %q", rootDir)
-	fs, err := ioutil.ReadDir(rootDir)
-	if err != nil {
-		return nil, fmt.Errorf("ReadDir(%s) failed: %v", rootDir, err)
-	}
-	var out []string
-	for _, f := range fs {
-		out = append(out, f.Name())
-	}
-	return out, nil
-}
-
-// State returns the metadata of the sandbox.
-func (s *Sandbox) State() specs.State {
-	return specs.State{
-		Version: specs.Version,
-		ID:      s.ID,
-		Status:  s.Status.String(),
-		Pid:     s.Pid,
-		Bundle:  s.BundleDir,
-	}
+	return s, nil
 }
 
 // Start starts running the containerized process inside the sandbox.
-func (s *Sandbox) Start(conf *boot.Config) error {
+func (s *Sandbox) Start(cid string, spec *specs.Spec, conf *boot.Config) error {
 	log.Debugf("Start sandbox %q, pid: %d", s.ID, s.Pid)
-	if s.Status != Created {
-		return fmt.Errorf("cannot start container in state %s", s.Status)
-	}
-
-	// "If any prestart hook fails, the runtime MUST generate an error,
-	// stop and destroy the container".
-	if s.Spec.Hooks != nil {
-		if err := executeHooks(s.Spec.Hooks.Prestart, s.State()); err != nil {
-			s.Destroy()
-			return err
-		}
-	}
-
-	c, err := s.connect()
+	conn, err := s.connect()
 	if err != nil {
-		s.Destroy()
 		return err
 	}
-	defer c.Close()
+	defer conn.Close()
 
 	// Configure the network.
-	if err := setupNetwork(c, s.Pid, s.Spec, conf); err != nil {
-		s.Destroy()
+	if err := setupNetwork(conn, s.Pid, spec, conf); err != nil {
 		return fmt.Errorf("error setting up network: %v", err)
 	}
 
 	// Send a message to the sandbox control server to start the
 	// application.
-	if err := c.Call(boot.ApplicationStart, nil, nil); err != nil {
-		s.Destroy()
-		return fmt.Errorf("error starting application %v: %v", s.Spec.Process.Args, err)
-	}
-
-	// "If any poststart hook fails, the runtime MUST log a warning, but
-	// the remaining hooks and lifecycle continue as if the hook had
-	// succeeded".
-	if s.Spec.Hooks != nil {
-		executeHooksBestEffort(s.Spec.Hooks.Poststart, s.State())
+	//
+	// TODO: Pass in the container id (cid) here. The sandbox
+	// should start only that container.
+	if err := conn.Call(boot.ApplicationStart, nil, nil); err != nil {
+		return fmt.Errorf("error starting application %v: %v", spec.Process.Args, err)
 	}
 
-	s.Status = Running
-	return s.save()
+	return nil
 }
 
-// Processes retrieves the list of processes and associated metadata inside a
-// sandbox.
-func (s *Sandbox) Processes() ([]*control.Process, error) {
-	if s.Status != Running {
-		return nil, fmt.Errorf("cannot get processes of container %q because it isn't running. It is in state %v", s.ID, s.Status)
-	}
-
-	c, err := s.connect()
+// Processes retrieves the list of processes and associated metadata for a
+// given container in this sandbox.
+func (s *Sandbox) Processes(cid string) ([]*control.Process, error) {
+	conn, err := s.connect()
 	if err != nil {
 		return nil, err
 	}
-	defer c.Close()
+	defer conn.Close()
 
 	var pl []*control.Process
-	if err := c.Call(boot.ApplicationProcesses, nil, &pl); err != nil {
+	// TODO: Pass in the container id (cid) here. The sandbox
+	// should return process info for only that container.
+	if err := conn.Call(boot.ApplicationProcesses, nil, &pl); err != nil {
 		return nil, fmt.Errorf("error retrieving process data from sandbox: %v", err)
 	}
 	return pl, nil
 }
 
-// Execute runs the specified command in the sandbox.
-func (s *Sandbox) Execute(e *control.ExecArgs) (syscall.WaitStatus, error) {
-	log.Debugf("Execute in sandbox %q, pid: %d, args: %+v", s.ID, s.Pid, e)
-	if s.Status != Created && s.Status != Running {
-		return 0, fmt.Errorf("cannot exec in container in state %s", s.Status)
-	}
-
-	log.Debugf("Connecting to sandbox...")
-	c, err := s.connect()
+// Execute runs the specified command in the container.
+func (s *Sandbox) Execute(cid string, e *control.ExecArgs) (syscall.WaitStatus, error) {
+	conn, err := s.connect()
 	if err != nil {
 		return 0, fmt.Errorf("error connecting to control server at pid %d: %v", s.Pid, err)
 	}
-	defer c.Close()
+	defer conn.Close()
 
 	// Send a message to the sandbox control server to start the application.
 	var waitStatus uint32
-	if err := c.Call(boot.ApplicationExecute, e, &waitStatus); err != nil {
+	// TODO: Pass in the container id (cid) here. The sandbox
+	// should execute in the context of that container.
+	if err := conn.Call(boot.ApplicationExecute, e, &waitStatus); err != nil {
 		return 0, fmt.Errorf("error executing in sandbox: %v", err)
 	}
 
@@ -347,60 +145,45 @@ func (s *Sandbox) Execute(e *control.ExecArgs) (syscall.WaitStatus, error) {
 }
 
 // Event retrieves stats about the sandbox such as memory and CPU utilization.
-func (s *Sandbox) Event() (*boot.Event, error) {
-	if s.Status != Running && s.Status != Created {
-		return nil, fmt.Errorf("cannot get events for container in state: %s", s.Status)
-	}
-
-	c, err := s.connect()
+func (s *Sandbox) Event(cid string) (*boot.Event, error) {
+	conn, err := s.connect()
 	if err != nil {
 		return nil, err
 	}
-	defer c.Close()
+	defer conn.Close()
 
 	var e boot.Event
-	if err := c.Call(boot.ApplicationEvent, nil, &e); err != nil {
+	// TODO: Pass in the container id (cid) here. The sandbox
+	// should return events only for that container.
+	if err := conn.Call(boot.ApplicationEvent, nil, &e); err != nil {
 		return nil, fmt.Errorf("error retrieving event data from sandbox: %v", err)
 	}
-	e.ID = s.ID
+	e.ID = cid
 	return &e, nil
 }
 
 func (s *Sandbox) connect() (*urpc.Client, error) {
 	log.Debugf("Connecting to sandbox...")
-	c, err := client.ConnectTo(boot.ControlSocketAddr(s.ID))
+	conn, err := client.ConnectTo(boot.ControlSocketAddr(s.ID))
 	if err != nil {
 		return nil, fmt.Errorf("error connecting to control server at pid %d: %v", s.Pid, err)
 	}
-	return c, nil
-}
-
-func (s *Sandbox) createProcesses(conf *boot.Config, args []string) error {
-	binPath, err := specutils.BinPath()
-	if err != nil {
-		return err
-	}
-
-	ioFiles, err := s.createGoferProcess(conf, binPath, args)
-	if err != nil {
-		return err
-	}
-	return s.createSandboxProcess(conf, binPath, args, ioFiles)
+	return conn, nil
 }
 
-func (s *Sandbox) createGoferProcess(conf *boot.Config, binPath string, commonArgs []string) ([]*os.File, error) {
+func (s *Sandbox) createGoferProcess(spec *specs.Spec, conf *boot.Config, bundleDir, binPath string) ([]*os.File, error) {
 	if conf.FileAccess != boot.FileAccessProxy {
 		// Don't start a gofer. The sandbox will access host FS directly.
 		return nil, nil
 	}
 
-	var args []string
-	args = append(args, commonArgs...)
-	args = append(args, "gofer", "--bundle", s.BundleDir)
+	// Start with the general config flags.
+	args := conf.ToFlags()
+	args = append(args, "gofer", "--bundle", bundleDir)
 
-	// Start with root mount and then add any other additional mount.
+	// Add root mount and then add any other additional mounts.
 	mountCount := 1
-	for _, m := range s.Spec.Mounts {
+	for _, m := range spec.Mounts {
 		if specutils.Is9PMount(m) {
 			mountCount++
 		}
@@ -429,8 +212,8 @@ func (s *Sandbox) createGoferProcess(conf *boot.Config, binPath string, commonAr
 	// Setup any uid/gid mappings, and create or join the configured user
 	// namespace so the gofer's view of the filesystem aligns with the
 	// users in the sandbox.
-	setUIDGIDMappings(cmd, s.Spec)
-	nss := filterNS([]specs.LinuxNamespaceType{specs.UserNamespace}, s.Spec)
+	setUIDGIDMappings(cmd, spec)
+	nss := filterNS([]specs.LinuxNamespaceType{specs.UserNamespace}, spec)
 
 	// Start the gofer in the given namespace.
 	log.Debugf("Starting gofer: %s %v", binPath, args)
@@ -444,7 +227,7 @@ func (s *Sandbox) createGoferProcess(conf *boot.Config, binPath string, commonAr
 
 // createSandboxProcess starts the sandbox as a subprocess by running the "boot"
 // command, passing in the bundle dir.
-func (s *Sandbox) createSandboxProcess(conf *boot.Config, binPath string, commonArgs []string, ioFiles []*os.File) error {
+func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, binPath string, ioFiles []*os.File) error {
 	// nextFD is used to get unused FDs that we can pass to the sandbox.  It
 	// starts at 3 because 0, 1, and 2 are taken by stdin/out/err.
 	nextFD := 3
@@ -457,13 +240,13 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, binPath string, common
 		return fmt.Errorf("error creating control server socket for sandbox %q: %v", s.ID, err)
 	}
 
-	consoleEnabled := s.ConsoleSocket != ""
+	consoleEnabled := consoleSocket != ""
 
-	cmd := exec.Command(binPath, commonArgs...)
+	cmd := exec.Command(binPath, conf.ToFlags()...)
 	cmd.SysProcAttr = &syscall.SysProcAttr{}
 	cmd.Args = append(cmd.Args,
 		"boot",
-		"--bundle", s.BundleDir,
+		"--bundle", bundleDir,
 		"--controller-fd="+strconv.Itoa(nextFD),
 		fmt.Sprintf("--console=%t", consoleEnabled))
 	nextFD++
@@ -485,9 +268,9 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, binPath string, common
 	if consoleEnabled {
 		// setupConsole will send the master on the socket, and return
 		// the slave.
-		tty, err := setupConsole(s.ConsoleSocket)
+		tty, err := setupConsole(consoleSocket)
 		if err != nil {
-			return fmt.Errorf("error setting up control socket %q: %v", s.ConsoleSocket, err)
+			return fmt.Errorf("error setting up control socket %q: %v", consoleSocket, err)
 		}
 		defer tty.Close()
 
@@ -535,7 +318,7 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, binPath string, common
 	// Joins the network namespace if network is enabled. the sandbox talks
 	// directly to the host network, which may have been configured in the
 	// namespace.
-	if ns, ok := getNS(specs.NetworkNamespace, s.Spec); ok && conf.Network != boot.NetworkNone {
+	if ns, ok := getNS(specs.NetworkNamespace, spec); ok && conf.Network != boot.NetworkNone {
 		log.Infof("Sandbox will be started in the container's network namespace: %+v", ns)
 		nss = append(nss, ns)
 	} else {
@@ -549,10 +332,10 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, binPath string, common
 	//   - Gofer: when using a Gofer, the sandbox process can run isolated in an
 	//       empty namespace.
 	if conf.Network == boot.NetworkHost || conf.FileAccess == boot.FileAccessDirect {
-		if userns, ok := getNS(specs.UserNamespace, s.Spec); ok {
+		if userns, ok := getNS(specs.UserNamespace, spec); ok {
 			log.Infof("Sandbox will be started in container's user namespace: %+v", userns)
 			nss = append(nss, userns)
-			setUIDGIDMappings(cmd, s.Spec)
+			setUIDGIDMappings(cmd, spec)
 		} else {
 			log.Infof("Sandbox will be started in the current user namespace")
 		}
@@ -596,8 +379,10 @@ func (s *Sandbox) waitForCreated(timeout time.Duration) error {
 }
 
 // Wait waits for the containerized process to exit, and returns its WaitStatus.
-func (s *Sandbox) Wait() (syscall.WaitStatus, error) {
-	log.Debugf("Wait on sandbox %q with pid %d", s.ID, s.Pid)
+func (s *Sandbox) Wait(cid string) (syscall.WaitStatus, error) {
+	// TODO: This waits on the sandbox process. We need a way
+	// to wait on an individual container in the sandbox.
+
 	p, err := os.FindProcess(s.Pid)
 	if err != nil {
 		// "On Unix systems, FindProcess always succeeds and returns a
@@ -611,6 +396,13 @@ func (s *Sandbox) Wait() (syscall.WaitStatus, error) {
 	return ps.Sys().(syscall.WaitStatus), nil
 }
 
+// Stop stops the container in the sandbox.
+func (s *Sandbox) Stop(cid string) error {
+	// TODO: This should stop the container with the given ID
+	// in the sandbox.
+	return nil
+}
+
 // Destroy frees all resources associated with the sandbox.
 func (s *Sandbox) Destroy() error {
 	log.Debugf("Destroy sandbox %q", s.ID)
@@ -625,60 +417,26 @@ func (s *Sandbox) Destroy() error {
 		sendSignal(s.GoferPid, unix.SIGKILL)
 		s.GoferPid = 0
 	}
-	if err := os.RemoveAll(s.SandboxRoot); err != nil {
-		log.Warningf("Failed to delete sandbox root directory %q, err: %v", s.SandboxRoot, err)
-	}
-
-	// "If any poststop hook fails, the runtime MUST log a warning, but the
-	// remaining hooks and lifecycle continue as if the hook had succeeded".
-	if s.Spec.Hooks != nil && (s.Status == Created || s.Status == Running) {
-		executeHooksBestEffort(s.Spec.Hooks.Poststop, s.State())
-	}
 
-	s.Status = Stopped
 	return nil
 }
 
-// Signal sends the signal to the sandbox.
-func (s *Sandbox) Signal(sig syscall.Signal) error {
+// Signal sends the signal to a container in the sandbox.
+func (s *Sandbox) Signal(cid string, sig syscall.Signal) error {
 	log.Debugf("Signal sandbox %q", s.ID)
-	if s.Status == Stopped {
-		log.Warningf("sandbox %q not running, not sending signal %v to pid %d", s.ID, sig, s.Pid)
-		return nil
-	}
+
+	// TODO: This sends a signal to the sandbox process, which
+	// will be forwarded to the first process in the sandbox. We need a way
+	// to send a signal to any container in the sandbox.
+	// to wait on an individual container in the sandbox.
+
 	return sendSignal(s.Pid, sig)
 }
 
+// sendSignal sends a signal to the sandbox process.
 func sendSignal(pid int, sig syscall.Signal) error {
 	if err := syscall.Kill(pid, sig); err != nil {
 		return fmt.Errorf("error sending signal %d to pid %d: %v", sig, pid, err)
 	}
 	return nil
 }
-
-// save saves the sandbox metadata to a file.
-func (s *Sandbox) save() error {
-	log.Debugf("Save sandbox %q", s.ID)
-	if err := os.MkdirAll(s.SandboxRoot, 0711); err != nil {
-		return fmt.Errorf("error creating sandbox root directory %q: %v", s.SandboxRoot, err)
-	}
-	meta, err := json.Marshal(s)
-	if err != nil {
-		return fmt.Errorf("error marshaling sandbox metadata: %v", err)
-	}
-	metaFile := filepath.Join(s.SandboxRoot, metadataFilename)
-	if err := ioutil.WriteFile(metaFile, meta, 0640); err != nil {
-		return fmt.Errorf("error writing sandbox metadata: %v", err)
-	}
-	return nil
-}
-
-// exists returns true if the given file exists.
-func exists(f string) bool {
-	if _, err := os.Stat(f); err == nil {
-		return true
-	} else if !os.IsNotExist(err) {
-		log.Warningf("error checking for file %q: %v", f, err)
-	}
-	return false
-}