Refactor to remove cmd from container

Pass the container's command via args
Remove execin function and just look for an
existing nspid file to join the namespace
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

pkg/libcontainer/container.go

@@ -5,17 +5,12 @@ type Container struct {
 	ReadonlyFs   bool         `json:"readonly_fs,omitempty"`
 	User         string       `json:"user,omitempty"`
 	WorkingDir   string       `json:"working_dir,omitempty"`
-	Command      *Command     `json:"command,omitempty"`
+	Env          []string     `json:"environment,omitempty"`
 	Namespaces   Namespaces   `json:"namespaces,omitempty"`
 	Capabilities Capabilities `json:"capabilities,omitempty"`
 	Network      *Network     `json:"network,omitempty"`
 }
 
-type Command struct {
-	Args []string `json:"args,omitempty"`
-	Env  []string `json:"environment,omitempty"`
-}
-
 type Network struct {
 	IP      string `json:"ip,omitempty"`
 	Gateway string `json:"gateway,omitempty"`

pkg/libcontainer/container.json

@@ -1,16 +1,11 @@
 {
     "hostname": "koye",
-    "command": {
-        "args": [
-            "/bin/bash"
-        ],
     "environment": [
         "HOME=/",
         "PATH=PATH=$PATH:/bin:/usr/bin:/sbin:/usr/sbin",
         "container=docker",
         "TERM=xterm-256color"
-        ]
+    ],
-    },
     "namespaces": [
         "NEWIPC",
         "NEWNS",

pkg/libcontainer/nsinit/exec.go

@@ -16,17 +16,13 @@ import (
 	"syscall"
 )
 
-func execCommand(container *libcontainer.Container) (int, error) {
+func execCommand(container *libcontainer.Container, args []string) (int, error) {
 	master, console, err := createMasterAndConsole()
 	if err != nil {
 		return -1, err
 	}
 
-	command := exec.Command("nsinit", "init", console)
+	command := createCommand(container, console, args)
-	command.SysProcAttr = &syscall.SysProcAttr{
-		Cloneflags: uintptr(getNamespaceFlags(container.Namespaces) | syscall.CLONE_VFORK), // we need CLONE_VFORK so we can wait on the child
-	}
-
 	// create a pipe so that we can syncronize with the namespaced process and
 	// pass the veth name to the child
 	inPipe, err := command.StdinPipe()
@@ -39,6 +35,7 @@ func execCommand(container *libcontainer.Container) (int, error) {
 	if err := writePidFile(command); err != nil {
 		return -1, err
 	}
+	defer deletePidFile()
 
 	if container.Network != nil {
 		vethPair, err := setupVeth(container.Network.Bridge, command.Process.Pid)
@@ -134,3 +131,15 @@ func createVethPair() (name1 string, name2 string, err error) {
 func writePidFile(command *exec.Cmd) error {
 	return ioutil.WriteFile(".nspid", []byte(fmt.Sprint(command.Process.Pid)), 0655)
 }
+
+func deletePidFile() error {
+	return os.Remove(".nspid")
+}
+
+func createCommand(container *libcontainer.Container, console string, args []string) *exec.Cmd {
+	command := exec.Command("nsinit", append([]string{"init", console}, args...)...)
+	command.SysProcAttr = &syscall.SysProcAttr{
+		Cloneflags: uintptr(getNamespaceFlags(container.Namespaces) | syscall.CLONE_VFORK), // we need CLONE_VFORK so we can wait on the child
+	}
+	return command
+}

pkg/libcontainer/nsinit/execin.go

@@ -5,19 +5,13 @@ import (
 	"github.com/dotcloud/docker/pkg/libcontainer"
 	"github.com/dotcloud/docker/pkg/libcontainer/capabilities"
 	"github.com/dotcloud/docker/pkg/system"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
 	"syscall"
 )
 
-func execinCommand(container *libcontainer.Container) (int, error) {
+func execinCommand(container *libcontainer.Container, nspid int, args []string) (int, error) {
-	nspid, err := readPid()
-	if err != nil {
-		return -1, err
-	}
-
 	for _, ns := range container.Namespaces {
 		if err := system.Unshare(namespaceMap[ns]); err != nil {
 			return -1, err
@@ -67,7 +61,7 @@ func execinCommand(container *libcontainer.Container) (int, error) {
 			if err := capabilities.DropCapabilities(container); err != nil {
 				return -1, fmt.Errorf("drop capabilities %s", err)
 			}
-			if err := system.Exec(container.Command.Args[0], container.Command.Args[0:], container.Command.Env); err != nil {
+			if err := system.Exec(args[0], args[0:], container.Env); err != nil {
 				return -1, err
 			}
 		}
@@ -84,24 +78,12 @@ func execinCommand(container *libcontainer.Container) (int, error) {
 	if err := capabilities.DropCapabilities(container); err != nil {
 		return -1, fmt.Errorf("drop capabilities %s", err)
 	}
-	if err := system.Exec(container.Command.Args[0], container.Command.Args[0:], container.Command.Env); err != nil {
+	if err := system.Exec(args[0], args[0:], container.Env); err != nil {
 		return -1, err
 	}
 	panic("unreachable")
 }
 
-func readPid() (int, error) {
-	data, err := ioutil.ReadFile(".nspid")
-	if err != nil {
-		return -1, err
-	}
-	pid, err := strconv.Atoi(string(data))
-	if err != nil {
-		return -1, err
-	}
-	return pid, nil
-}
-
 func getNsFds(pid int, container *libcontainer.Container) ([]uintptr, error) {
 	fds := make([]uintptr, len(container.Namespaces))
 	for i, ns := range container.Namespaces {

pkg/libcontainer/nsinit/init.go

@@ -14,7 +14,7 @@ import (
 	"syscall"
 )
 
-func initCommand(container *libcontainer.Container, console string) error {
+func initCommand(container *libcontainer.Container, console string, args []string) error {
 	rootfs, err := resolveRootfs()
 	if err != nil {
 		return err
@@ -72,7 +72,7 @@ func initCommand(container *libcontainer.Container, console string) error {
 			return fmt.Errorf("chdir to %s %s", container.WorkingDir, err)
 		}
 	}
-	if err := system.Exec(container.Command.Args[0], container.Command.Args[0:], container.Command.Env); err != nil {
+	if err := system.Exec(args[0], args[0:], container.Env); err != nil {
 		return fmt.Errorf("exec %s", err)
 	}
 	panic("unreachable")

pkg/libcontainer/nsinit/main.go

@@ -4,8 +4,10 @@ import (
 	"encoding/json"
 	"errors"
 	"github.com/dotcloud/docker/pkg/libcontainer"
+	"io/ioutil"
 	"log"
 	"os"
+	"strconv"
 )
 
 var (
@@ -25,24 +27,29 @@ func main() {
 	}
 	switch os.Args[1] {
 	case "exec":
-		exitCode, err := execCommand(container)
+		var exitCode int
+		nspid, err := readPid()
+		if err != nil {
+			if !os.IsNotExist(err) {
+				log.Fatal(err)
+			}
+		}
+		if nspid > 0 {
+			exitCode, err = execinCommand(container, nspid, os.Args[2:])
+		} else {
+			exitCode, err = execCommand(container, os.Args[2:])
+		}
 		if err != nil {
 			log.Fatal(err)
 		}
 		os.Exit(exitCode)
 	case "init":
-		if argc != 3 {
+		if argc < 3 {
 			log.Fatal(ErrWrongArguments)
 		}
-		if err := initCommand(container, os.Args[2]); err != nil {
+		if err := initCommand(container, os.Args[2], os.Args[3:]); err != nil {
 			log.Fatal(err)
 		}
-	case "execin":
-		exitCode, err := execinCommand(container)
-		if err != nil {
-			log.Fatal(err)
-		}
-		os.Exit(exitCode)
 	default:
 		log.Fatalf("command not supported for nsinit %s", os.Args[1])
 	}
@@ -61,3 +68,15 @@ func loadContainer() (*libcontainer.Container, error) {
 	}
 	return container, nil
 }
+
+func readPid() (int, error) {
+	data, err := ioutil.ReadFile(".nspid")
+	if err != nil {
+		return -1, err
+	}
+	pid, err := strconv.Atoi(string(data))
+	if err != nil {
+		return -1, err
+	}
+	return pid, nil
+}