Implement CreateContainer

Signed-off-by: Haiyan Meng <hmeng@redhat.com>

utils/utils.go

@@ -3,7 +3,9 @@ package utils
 import (
 	"bytes"
 	"fmt"
+	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"syscall"
 )
@@ -25,6 +27,21 @@ func ExecCmd(name string, args ...string) (string, error) {
 	return stdout.String(), nil
 }
 
+// ExecCmdWithStdStreams execute a command with the specified standard streams.
+func ExecCmdWithStdStreams(stdin, stdout, stderr *os.File, name string, args ...string) error {
+	cmd := exec.Command(name, args...)
+	cmd.Stdin = stdin
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("`%v %v` failed: %v", name, strings.Join(args, " "), err)
+	}
+
+	return nil
+}
+
 // SetSubreaper sets the value i as the subreaper setting for the calling process
 func SetSubreaper(i int) error {
 	return Prctl(PR_SET_CHILD_SUBREAPER, uintptr(i), 0, 0, 0)
@@ -38,3 +55,45 @@ func Prctl(option int, arg2, arg3, arg4, arg5 uintptr) (err error) {
 	}
 	return
 }
+
+// CreateFakeRootfs creates a fake rootfs for test.
+func CreateFakeRootfs(dir string, image string) error {
+	if len(image) <= 9 || image[:9] != "docker://" {
+		return fmt.Errorf("CreateFakeRootfs only support docker images currently")
+	}
+
+	rootfs := filepath.Join(dir, "rootfs")
+	if err := os.MkdirAll(rootfs, 0755); err != nil {
+		return err
+	}
+
+	// docker export $(docker create image[9:]) | tar -C rootfs -xf -
+	return dockerExport(image[9:], rootfs)
+}
+
+func dockerExport(image string, rootfs string) error {
+	out, err := ExecCmd("docker", "create", image)
+	if err != nil {
+		return err
+	}
+
+	container := out[:strings.Index(out, "\n")]
+
+	cmd := fmt.Sprintf("docker export %s | tar -C %s -xf -", container, rootfs)
+	if _, err := ExecCmd("/bin/bash", "-c", cmd); err != nil {
+		err1 := dockerRemove(container)
+		if err1 == nil {
+			return err
+		}
+		return fmt.Errorf("%v; %v", err, err1)
+	}
+
+	return dockerRemove(container)
+}
+
+func dockerRemove(container string) error {
+	if _, err := ExecCmd("docker", "rm", container); err != nil {
+		return err
+	}
+	return nil
+}