add support for testing execin

when the test binary starts, it detects whether it should run the container
initialization code or the execin initialization code based on the suppplied
arguments. The execin initialization code is taken from docker.

also added a sample test for execin process.

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)

integration/execin_test.go

@@ -0,0 +1,83 @@
+package integration
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/docker/libcontainer"
+	"github.com/docker/libcontainer/namespaces"
+)
+
+func TestExecIn(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+
+	rootfs, err := newRootFs()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer remove(rootfs)
+
+	config := newTemplateConfig(rootfs)
+	if err := writeConfig(config); err != nil {
+		t.Fatalf("failed to write config %s", err)
+	}
+
+	// start the container
+	containerErr := make(chan error, 1)
+	containerCmd := &exec.Cmd{}
+	var statePath string
+	createCmd := func(container *libcontainer.Config, console, dataPath, init string,
+		pipe *os.File, args []string) *exec.Cmd {
+		containerCmd = namespaces.DefaultCreateCommand(container, console, dataPath, init, pipe, args)
+		statePath = dataPath
+		return containerCmd
+	}
+	var containerStart sync.WaitGroup
+	containerStart.Add(1)
+	go func() {
+		buffers := newStdBuffers()
+		_, err := namespaces.Exec(config,
+			buffers.Stdin, buffers.Stdout, buffers.Stderr,
+			"", config.RootFs, []string{"sleep", "10"},
+			createCmd, containerStart.Done)
+		containerErr <- err
+	}()
+	containerStart.Wait()
+
+	defer func() {
+		// kill the container
+		if containerCmd.Process != nil {
+			containerCmd.Process.Kill()
+		}
+		if err := <-containerErr; err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	// start the exec process
+	state, err := libcontainer.GetState(statePath)
+	if err != nil {
+		t.Fatalf("failed to get state %s", err)
+	}
+	buffers := newStdBuffers()
+	execErr := make(chan error, 1)
+	go func() {
+		_, err := namespaces.ExecIn(config, state, []string{"ps"},
+			os.Args[0], "exec", buffers.Stdin, buffers.Stdout, buffers.Stderr,
+			"", nil)
+		execErr <- err
+	}()
+	if err := <-execErr; err != nil {
+		t.Fatalf("exec finished with error %s", err)
+	}
+
+	out := buffers.Stdout.String()
+	if !strings.Contains(out, "sleep 10") || !strings.Contains(out, "ps") {
+		t.Fatalf("unexpected running process, output %q", out)
+	}
+}

integration/init_test.go

@@ -1,19 +1,24 @@
 package integration
 
 import (
+	"encoding/json"
 	"log"
 	"os"
 	"runtime"
 
+	"github.com/docker/libcontainer"
 	"github.com/docker/libcontainer/namespaces"
+	_ "github.com/docker/libcontainer/namespaces/nsenter"
 )
 
 // init runs the libcontainer initialization code because of the busybox style needs
 // to work around the go runtime and the issues with forking
 func init() {
-	if len(os.Args) < 2 || os.Args[1] != "init" {
+	if len(os.Args) < 2 {
 		return
 	}
+	// handle init
+	if len(os.Args) >= 2 && os.Args[1] == "init" {
 		runtime.LockOSThread()
 
 		container, err := loadConfig()
@@ -31,3 +36,41 @@ func init() {
 		}
 		os.Exit(1)
 	}
+
+	// handle execin
+	if len(os.Args) >= 2 && os.Args[0] == "nsenter-exec" {
+		runtime.LockOSThread()
+
+		// User args are passed after '--' in the command line.
+		userArgs := findUserArgs()
+
+		config, err := loadConfigFromFd()
+		if err != nil {
+			log.Fatalf("docker-exec: unable to receive config from sync pipe: %s", err)
+		}
+
+		if err := namespaces.FinalizeSetns(config, userArgs); err != nil {
+			log.Fatalf("docker-exec: failed to exec: %s", err)
+		}
+		os.Exit(1)
+	}
+}
+
+func findUserArgs() []string {
+	for i, a := range os.Args {
+		if a == "--" {
+			return os.Args[i+1:]
+		}
+	}
+	return []string{}
+}
+
+// loadConfigFromFd loads a container's config from the sync pipe that is provided by
+// fd 3 when running a process
+func loadConfigFromFd() (*libcontainer.Config, error) {
+	var config *libcontainer.Config
+	if err := json.NewDecoder(os.NewFile(3, "child")).Decode(&config); err != nil {
+		return nil, err
+	}
+	return config, nil
+}