Split out into a small stub command line and a library

- this is pretty much the smallest change to split this out and it
  exposes a few things that can be improved later
- no change to logging yet

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

src/moby/linuxkit.go

@@ -0,0 +1,148 @@
+package moby
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	log "github.com/Sirupsen/logrus"
+)
+
+var linuxkitYaml = map[string]string{"mkimage": `
+kernel:
+  image: "linuxkit/kernel:4.9.x"
+  cmdline: "console=ttyS0"
+init:
+  - linuxkit/init:1b8a7e394d2ec2f1fdb4d67645829d1b5bdca037
+  - linuxkit/runc:3a4e6cbf15470f62501b019b55e1caac5ee7689f
+  - linuxkit/containerd:b1766e4c4c09f63ac4925a6e4612852a93f7e73b
+onboot:
+  - name: mkimage
+    image: "linuxkit/mkimage:5ad60299be03008f29c5caec3c5ea4ac0387aae6"
+  - name: poweroff
+    image: "linuxkit/poweroff:a8f1e4ad8d459f1fdaad9e4b007512cb3b504ae8"
+trust:
+  org:
+    - linuxkit
+`}
+
+func imageFilename(name string) string {
+	yaml := linuxkitYaml[name]
+	hash := sha256.Sum256([]byte(yaml))
+	return filepath.Join(MobyDir, "linuxkit", name+"-"+fmt.Sprintf("%x", hash))
+}
+
+func ensureLinuxkitImage(name string) error {
+	filename := imageFilename(name)
+	_, err1 := os.Stat(filename + "-kernel")
+	_, err2 := os.Stat(filename + "-initrd.img")
+	_, err3 := os.Stat(filename + "-cmdline")
+	if err1 == nil && err2 == nil && err3 == nil {
+		return nil
+	}
+	err := os.MkdirAll(filepath.Join(MobyDir, "linuxkit"), 0755)
+	if err != nil {
+		return err
+	}
+	// TODO clean up old files
+	log.Infof("Building LinuxKit image %s to generate output formats", name)
+
+	yaml := linuxkitYaml[name]
+
+	m, err := NewConfig([]byte(yaml))
+	if err != nil {
+		return err
+	}
+	// TODO pass through --pull to here
+	buf := new(bytes.Buffer)
+	Build(m, buf, false, "")
+	image := buf.Bytes()
+	kernel, initrd, cmdline, err := tarToInitrd(image)
+	if err != nil {
+		return fmt.Errorf("Error converting to initrd: %v", err)
+	}
+	err = writeKernelInitrd(filename, kernel, initrd, cmdline)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func writeKernelInitrd(filename string, kernel []byte, initrd []byte, cmdline string) error {
+	err := ioutil.WriteFile(filename+"-kernel", kernel, 0600)
+	if err != nil {
+		return err
+	}
+	err = ioutil.WriteFile(filename+"-initrd.img", initrd, 0600)
+	if err != nil {
+		return err
+	}
+	err = ioutil.WriteFile(filename+"-cmdline", []byte(cmdline), 0600)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func outputLinuxKit(format string, filename string, kernel []byte, initrd []byte, cmdline string, size int, hyperkit bool) error {
+	log.Debugf("output linuxkit generated img: %s %s size %d", format, filename, size)
+
+	tmp, err := ioutil.TempDir(filepath.Join(MobyDir, "tmp"), "moby")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(tmp)
+
+	buf, err := tarInitrdKernel(kernel, initrd, cmdline)
+	if err != nil {
+		return err
+	}
+
+	tardisk := filepath.Join(tmp, "tardisk")
+	f, err := os.Create(tardisk)
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(f, buf)
+	if err != nil {
+		return err
+	}
+	err = f.Close()
+	if err != nil {
+		return err
+	}
+
+	sizeString := fmt.Sprintf("%dM", size)
+	_ = os.Remove(filename)
+	_, err = os.Stat(filename)
+	if err == nil || !os.IsNotExist(err) {
+		return fmt.Errorf("Cannot remove existing file [%s]", filename)
+	}
+	linuxkit, err := exec.LookPath("linuxkit")
+	if err != nil {
+		return fmt.Errorf("Cannot find linuxkit executable, needed to build %s output type: %v", format, err)
+	}
+	commandLine := []string{"-q", "run", "qemu", "-disk", fmt.Sprintf("%s,size=%s,format=%s", filename, sizeString, format), "-disk", fmt.Sprintf("%s,format=raw", tardisk), "-kernel", imageFilename("mkimage")}
+	if hyperkit && format == "raw" {
+		state, err := ioutil.TempDir("", "s")
+		if err != nil {
+			return err
+		}
+		defer os.RemoveAll(state)
+		commandLine = []string{"-q", "run", "hyperkit", "-state", state, "-disk", fmt.Sprintf("%s,size=%s,format=%s", filename, sizeString, format), "-disk", fmt.Sprintf("%s,format=raw", tardisk), imageFilename("mkimage")}
+	}
+	log.Debugf("run %s: %v", linuxkit, commandLine)
+	cmd := exec.Command(linuxkit, commandLine...)
+	cmd.Stderr = os.Stderr
+	err = cmd.Run()
+	if err != nil {
+		return err
+	}
+	return nil
+}