Remove statewriter interface, export more libcontainer funcs

This temp. expands the Exec method's signature but adds a more robust
way to know when the container's process is actually released and begins
to run.  The network interfaces are not guaranteed to be up yet but this
provides a more accurate view with a single callback at this time.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/nsinit/exec.go

@@ -3,8 +3,11 @@
 package nsinit
 
 import (
+	"fmt"
+	"io/ioutil"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"syscall"
 
 	"github.com/dotcloud/docker/pkg/cgroups"
@@ -17,7 +20,7 @@ import (
 
 // Exec performes setup outside of a namespace so that a container can be
 // executed.  Exec is a high level function for working with container namespaces.
-func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, args []string) (int, error) {
+func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, pidRoot string, args []string, startCallback func()) (int, error) {
 	var (
 		master  *os.File
 		console string
@@ -53,24 +56,24 @@ func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, args [
 	if err != nil {
 		return -1, err
 	}
-	if err := ns.stateWriter.WritePid(command.Process.Pid, started); err != nil {
+	if err := WritePid(pidRoot, command.Process.Pid, started); err != nil {
 		command.Process.Kill()
 		return -1, err
 	}
-	defer ns.stateWriter.DeletePid()
+	defer DeletePid(pidRoot)
 
 	// Do this before syncing with child so that no children
 	// can escape the cgroup
-	activeCgroup, err := ns.SetupCgroups(container, command.Process.Pid)
+	cleaner, err := SetupCgroups(container, command.Process.Pid)
 	if err != nil {
 		command.Process.Kill()
 		return -1, err
 	}
-	if activeCgroup != nil {
+	if cleaner != nil {
-		defer activeCgroup.Cleanup()
+		defer cleaner.Cleanup()
 	}
 
-	if err := ns.InitializeNetworking(container, command.Process.Pid, syncPipe); err != nil {
+	if err := InitializeNetworking(container, command.Process.Pid, syncPipe); err != nil {
 		command.Process.Kill()
 		return -1, err
 	}
@@ -78,6 +81,10 @@ func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, args [
 	// Sync with child
 	syncPipe.Close()
 
+	if startCallback != nil {
+		startCallback()
+	}
+
 	if err := command.Wait(); err != nil {
 		if _, ok := err.(*exec.ExitError); !ok {
 			return -1, err
@@ -87,7 +94,9 @@ func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, args [
 	return status, err
 }
 
-func (ns *linuxNs) SetupCgroups(container *libcontainer.Container, nspid int) (cgroups.ActiveCgroup, error) {
+// SetupCgroups applies the cgroup restrictions to the process running in the contaienr based
+// on the container's configuration
+func SetupCgroups(container *libcontainer.Container, nspid int) (cgroups.ActiveCgroup, error) {
 	if container.Cgroups != nil {
 		c := container.Cgroups
 		if systemd.UseSystemd() {
@@ -98,7 +107,9 @@ func (ns *linuxNs) SetupCgroups(container *libcontainer.Container, nspid int) (c
 	return nil, nil
 }
 
-func (ns *linuxNs) InitializeNetworking(container *libcontainer.Container, nspid int, pipe *SyncPipe) error {
+// InitializeNetworking creates the container's network stack outside of the namespace and moves
+// interfaces into the container's net namespaces if necessary
+func InitializeNetworking(container *libcontainer.Container, nspid int, pipe *SyncPipe) error {
 	context := libcontainer.Context{}
 	for _, config := range container.Networks {
 		strategy, err := network.GetStrategy(config.Type)
@@ -111,3 +122,23 @@ func (ns *linuxNs) InitializeNetworking(container *libcontainer.Container, nspid
 	}
 	return pipe.SendToChild(context)
 }
+
+// WritePid writes the namespaced processes pid to pid and it's start time
+// to the path specified
+func WritePid(path string, pid int, startTime string) error {
+	err := ioutil.WriteFile(filepath.Join(path, "pid"), []byte(fmt.Sprint(pid)), 0655)
+	if err != nil {
+		return err
+	}
+	return ioutil.WriteFile(filepath.Join(path, "start"), []byte(startTime), 0655)
+}
+
+// DeletePid removes the pid and started file from disk when the container's process
+// dies and the container is cleanly removed
+func DeletePid(path string) error {
+	err := os.Remove(filepath.Join(path, "pid"))
+	if serr := os.Remove(filepath.Join(path, "start")); err == nil {
+		err = serr
+	}
+	return err
+}

libcontainer/nsinit/nsinit.go

@@ -5,7 +5,7 @@ import "github.com/dotcloud/docker/pkg/libcontainer"
 // NsInit is an interface with the public facing methods to provide high level
 // exec operations on a container
 type NsInit interface {
-	Exec(container *libcontainer.Container, term Terminal, args []string) (int, error)
+	Exec(container *libcontainer.Container, term Terminal, pidRoot string, args []string, startCallback func()) (int, error)
 	ExecIn(container *libcontainer.Container, nspid int, args []string) (int, error)
 	Init(container *libcontainer.Container, uncleanRootfs, console string, syncPipe *SyncPipe, args []string) error
 }
@@ -13,12 +13,10 @@ type NsInit interface {
 type linuxNs struct {
 	root           string
 	commandFactory CommandFactory
-	stateWriter    StateWriter
 }
 
-func NewNsInit(command CommandFactory, state StateWriter) NsInit {
+func NewNsInit(command CommandFactory) NsInit {
 	return &linuxNs{
 		commandFactory: command,
-		stateWriter:    state,
 	}
 }

libcontainer/nsinit/nsinit/main.go

@@ -56,7 +56,7 @@ func main() {
 			exitCode, err = ns.ExecIn(container, nspid, flag.Args()[1:])
 		} else {
 			term := nsinit.NewTerminal(os.Stdin, os.Stdout, os.Stderr, container.Tty)
-			exitCode, err = ns.Exec(container, term, flag.Args()[1:])
+			exitCode, err = ns.Exec(container, term, root, flag.Args()[1:], nil)
 		}
 		if err != nil {
 			log.Fatalf("Failed to exec: %s", err)
@@ -109,5 +109,5 @@ func readPid() (int, error) {
 }
 
 func newNsInit() (nsinit.NsInit, error) {
-	return nsinit.NewNsInit(&nsinit.DefaultCommandFactory{root}, &nsinit.DefaultStateWriter{root}), nil
+	return nsinit.NewNsInit(&nsinit.DefaultCommandFactory{root}), nil
 }

libcontainer/nsinit/state.go

@@ -1,36 +0,0 @@
-package nsinit
-
-import (
-	"fmt"
-	"io/ioutil"
-	"os"
-	"path/filepath"
-)
-
-// StateWriter handles writing and deleting the pid file
-// on disk
-type StateWriter interface {
-	WritePid(pid int, startTime string) error
-	DeletePid() error
-}
-
-type DefaultStateWriter struct {
-	Root string
-}
-
-// writePidFile writes the namespaced processes pid to pid in the rootfs for the container
-func (d *DefaultStateWriter) WritePid(pid int, startTime string) error {
-	err := ioutil.WriteFile(filepath.Join(d.Root, "pid"), []byte(fmt.Sprint(pid)), 0655)
-	if err != nil {
-		return err
-	}
-	return ioutil.WriteFile(filepath.Join(d.Root, "start"), []byte(startTime), 0655)
-}
-
-func (d *DefaultStateWriter) DeletePid() error {
-	err := os.Remove(filepath.Join(d.Root, "pid"))
-	if serr := os.Remove(filepath.Join(d.Root, "start")); err == nil {
-		err = serr
-	}
-	return err
-}

libcontainer/nsinit/unsupported.go

@@ -6,7 +6,7 @@ import (
 	"github.com/dotcloud/docker/pkg/libcontainer"
 )
 
-func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, args []string) (int, error) {
+func (ns *linuxNs) Exec(container *libcontainer.Container, term Terminal, pidRoot string, args []string, startCallback func()) (int, error) {
 	return -1, libcontainer.ErrUnsupported
 }