runc/nsinit/exec.go

package nsinit

import (
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"os/signal"
	"syscall"

	"github.com/codegangsta/cli"
	"github.com/docker/libcontainer"
	consolepkg "github.com/docker/libcontainer/console"
	"github.com/docker/libcontainer/namespaces"
	"github.com/dotcloud/docker/pkg/term"
)

var execCommand = cli.Command{
	Name:   "exec",
	Usage:  "execute a new command inside a container",
	Action: execAction,
}

func execAction(context *cli.Context) {
	var exitCode int

	container, err := loadContainer()
	if err != nil {
		log.Fatal(err)
	}

	state, err := libcontainer.GetState(dataPath)
	if err != nil && !os.IsNotExist(err) {
		log.Fatalf("unable to read state.json: %s", err)
	}

	if state != nil {
		err = namespaces.ExecIn(container, state, []string(context.Args()))
	} else {
		exitCode, err = startContainer(container, dataPath, []string(context.Args()))
	}

	if err != nil {
		log.Fatalf("failed to exec: %s", err)
	}

	os.Exit(exitCode)
}

// startContainer starts the container. Returns the exit status or -1 and an
// error.
//
// Signals sent to the current process will be forwarded to container.
func startContainer(container *libcontainer.Config, dataPath string, args []string) (int, error) {
	var (
		cmd  *exec.Cmd
		sigc = make(chan os.Signal, 10)
	)

	signal.Notify(sigc)

	createCommand := func(container *libcontainer.Config, console, rootfs, dataPath, init string, pipe *os.File, args []string) *exec.Cmd {
		cmd = namespaces.DefaultCreateCommand(container, console, rootfs, dataPath, init, pipe, args)
		if logPath != "" {
			cmd.Env = append(cmd.Env, fmt.Sprintf("log=%s", logPath))
		}
		return cmd
	}

	startCallback := func() {
		go func() {
			for sig := range sigc {
				cmd.Process.Signal(sig)
			}
		}()
	}

	var (
		stdin  = os.Stdin
		stdout = os.Stdout
		stderr = os.Stderr
	)

	if container.Tty {
		master, slavePath, err := consolepkg.CreateMasterAndConsole()
		if err != nil {
			return -1, err
		}

		slave, err := consolepkg.OpenTerminal(slavePath, syscall.O_RDWR|syscall.O_NOCTTY)
		if err != nil {
			return -1, err
		}

		stdin, stdout, stderr = slave, slave, slave

		go io.Copy(master, os.Stdin)
		go io.Copy(os.Stdout, master)

		ws, err := term.GetWinsize(os.Stdin.Fd())
		if err != nil {
			return -1, err
		}

		if err := term.SetWinsize(master.Fd(), ws); err != nil {
			return -1, err
		}

		if _, err := term.SetRawTerminal(os.Stdin.Fd()); err != nil {
			return -1, err
		}
	}

	return namespaces.Exec(container, stdin, stdout, stderr, "", dataPath, args, createCommand, startCallback)
}