Merge pull request #64 from vishh/runin

Adding RunIn to run a user specified command in an existing container.

namespaces/execin.go

@@ -4,32 +4,96 @@ package namespaces
 
 import (
 	"encoding/json"
-	"os"
-	"strconv"
-
 	"github.com/docker/libcontainer"
 	"github.com/docker/libcontainer/label"
 	"github.com/docker/libcontainer/system"
+	"io"
+	"os"
+	"os/exec"
+	"strconv"
+	"syscall"
 )
 
+// Runs the command under 'args' inside an existing container referred to by 'container'.
+// Returns the exitcode of the command upon success and appropriate error on failure.
+func RunIn(container *libcontainer.Config, state *libcontainer.State, args []string, nsinitPath string, stdin io.Reader, stdout, stderr io.Writer, console string, startCallback func(*exec.Cmd)) (int, error) {
+	initArgs, err := getNsEnterCommand(strconv.Itoa(state.InitPid), container, console, args)
+	if err != nil {
+		return -1, err
+	}
+
+	cmd := exec.Command(nsinitPath, initArgs...)
+	// Note: these are only used in non-tty mode
+	// if there is a tty for the container it will be opened within the namespace and the
+	// fds will be duped to stdin, stdiout, and stderr
+	cmd.Stdin = stdin
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+
+	if err := cmd.Start(); err != nil {
+		return -1, err
+	}
+	if startCallback != nil {
+		startCallback(cmd)
+	}
+
+	if err := cmd.Wait(); err != nil {
+		if _, ok := err.(*exec.ExitError); !ok {
+			return -1, err
+		}
+	}
+
+	return cmd.ProcessState.Sys().(syscall.WaitStatus).ExitStatus(), nil
+}
+
 // ExecIn uses an existing pid and joins the pid's namespaces with the new command.
 func ExecIn(container *libcontainer.Config, state *libcontainer.State, args []string) error {
-	// TODO(vmarmol): If this gets too long, send it over a pipe to the child.
+	// Enter the namespace and then finish setup
-	// Marshall the container into JSON since it won't be available in the namespace.
+	args, err := getNsEnterCommand(strconv.Itoa(state.InitPid), container, "", args)
-	containerJson, err := json.Marshal(container)
 	if err != nil {
 		return err
 	}
 
-	// Enter the namespace and then finish setup
+	finalArgs := append([]string{os.Args[0]}, args...)
-	finalArgs := []string{os.Args[0], "nsenter", "--nspid", strconv.Itoa(state.InitPid), "--containerjson", string(containerJson), "--"}
+
-	finalArgs = append(finalArgs, args...)
 	if err := system.Execv(finalArgs[0], finalArgs[0:], os.Environ()); err != nil {
 		return err
 	}
+
 	panic("unreachable")
 }
 
+func getContainerJson(container *libcontainer.Config) (string, error) {
+	// TODO(vmarmol): If this gets too long, send it over a pipe to the child.
+	// Marshall the container into JSON since it won't be available in the namespace.
+	containerJson, err := json.Marshal(container)
+	if err != nil {
+		return "", err
+	}
+	return string(containerJson), nil
+}
+
+func getNsEnterCommand(initPid string, container *libcontainer.Config, console string, args []string) ([]string, error) {
+	containerJson, err := getContainerJson(container)
+	if err != nil {
+		return nil, err
+	}
+
+	out := []string{
+		"nsenter",
+		"--nspid", initPid,
+		"--containerjson", containerJson,
+	}
+
+	if console != "" {
+		out = append(out, "--console", console)
+	}
+	out = append(out, "--")
+	out = append(out, args...)
+
+	return out, nil
+}
+
 // Run a command in a container after entering the namespace.
 func NsEnter(container *libcontainer.Config, args []string) error {
 	// clear the current processes env and replace it with the environment

namespaces/nsenter.go

@@ -88,6 +88,7 @@ void nsenter() {
 	static const struct option longopts[] = {
 		{ "nspid",         required_argument, NULL, 'n' },
 		{ "containerjson", required_argument, NULL, 'c' },
+                { "console",       required_argument, NULL, 't' },
 		{ NULL,            0,                 NULL,  0  }
 	};
 
@@ -95,6 +96,7 @@ void nsenter() {
 	pid_t init_pid = -1;
 	char *init_pid_str = NULL;
 	char *container_json = NULL;
+        char *console = NULL;
 	while ((c = getopt_long_only(argc, argv, "n:s:c:", longopts, NULL)) != -1) {
 		switch (c) {
 		case 'n':
@@ -103,6 +105,9 @@ void nsenter() {
 		case 'c':
 			container_json = optarg;
 			break;
+		case 't':
+			console = optarg;
+			break;
 		}
 	}
 
@@ -121,6 +126,21 @@ void nsenter() {
 	argc -= 3;
 	argv += 3;
 
+        if (setsid() == -1) {
+               fprintf(stderr, "setsid failed. Error: %s\n", strerror(errno));
+               exit(1);
+        }
+
+        // before we setns we need to dup the console
+        int consolefd = -1;
+        if (console != NULL) {
+               consolefd = open(console, O_RDWR);
+               if (consolefd < 0) {
+                    fprintf(stderr, "nsenter: failed to open console %s\n", console, strerror(errno));
+                    exit(1);
+              }
+        }
+
 	// Setns on all supported namespaces.
 	char ns_dir[PATH_MAX];
 	memset(ns_dir, 0, PATH_MAX);
@@ -159,6 +179,21 @@ void nsenter() {
 	// We must fork to actually enter the PID namespace.
 	int child = fork();
 	if (child == 0) {
+       if (consolefd != -1) {
+        if (dup2(consolefd, STDIN_FILENO) != 0) {
+            fprintf(stderr, "nsenter: failed to dup 0 %s\n",  strerror(errno));
+            exit(1);
+        }
+        if (dup2(consolefd, STDOUT_FILENO) != STDOUT_FILENO) {
+            fprintf(stderr, "nsenter: failed to dup 1 %s\n",  strerror(errno));
+            exit(1);
+        }
+        if (dup2(consolefd, STDERR_FILENO) != STDERR_FILENO) {
+            fprintf(stderr, "nsenter: failed to dup 2 %s\n",  strerror(errno));
+            exit(1);
+        }
+}
+
 		// Finish executing, let the Go runtime take over.
 		return;
 	} else {

nsinit/exec.go

@@ -36,7 +36,7 @@ func execAction(context *cli.Context) {
 	}
 
 	if state != nil {
-		err = namespaces.ExecIn(container, state, []string(context.Args()))
+		exitCode, err = runIn(container, state, []string(context.Args()))
 	} else {
 		exitCode, err = startContainer(container, dataPath, []string(context.Args()))
 	}
@@ -48,6 +48,59 @@ func execAction(context *cli.Context) {
 	os.Exit(exitCode)
 }
 
+func runIn(container *libcontainer.Config, state *libcontainer.State, args []string) (int, error) {
+	var (
+		master  *os.File
+		console string
+		err     error
+
+		stdin  = os.Stdin
+		stdout = os.Stdout
+		stderr = os.Stderr
+		sigc   = make(chan os.Signal, 10)
+	)
+
+	signal.Notify(sigc)
+
+	if container.Tty {
+		stdin = nil
+		stdout = nil
+		stderr = nil
+
+		master, console, err = consolepkg.CreateMasterAndConsole()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		go io.Copy(master, os.Stdin)
+		go io.Copy(os.Stdout, master)
+
+		state, err := term.SetRawTerminal(os.Stdin.Fd())
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		defer term.RestoreTerminal(os.Stdin.Fd(), state)
+	}
+
+	startCallback := func(cmd *exec.Cmd) {
+		go func() {
+			resizeTty(master)
+
+			for sig := range sigc {
+				switch sig {
+				case syscall.SIGWINCH:
+					resizeTty(master)
+				default:
+					cmd.Process.Signal(sig)
+				}
+			}
+		}()
+	}
+
+	return namespaces.RunIn(container, state, args, os.Args[0], stdin, stdout, stderr, console, startCallback)
+}
+
 // startContainer starts the container. Returns the exit status or -1 and an
 // error.
 //

nsinit/nsenter.go

@@ -14,6 +14,7 @@ var nsenterCommand = cli.Command{
 	Flags: []cli.Flag{
 		cli.IntFlag{Name: "nspid"},
 		cli.StringFlag{Name: "containerjson"},
+		cli.StringFlag{Name: "console"},
 	},
 }