package main import ( "archive/tar" "compress/gzip" "fmt" "io" "io/ioutil" "log" "os" "os/exec" "path/filepath" "strings" "syscall" "github.com/pierrec/lz4" ) func buildBootImg(out io.Writer, ctx *renderContext) (err error) { bootImg, err := ioutil.TempFile(os.TempDir(), "boot.img-") if err != nil { return } defer rmTempFile(bootImg) err = setupBootImage(bootImg, ctx) if err != nil { return } // send the result bootImg.Seek(0, os.SEEK_SET) io.Copy(out, bootImg) return } func buildBootImgLZ4(out io.Writer, ctx *renderContext) (err error) { lz4Out := lz4.NewWriter(out) if err = buildBootImg(lz4Out, ctx); err != nil { return } lz4Out.Close() return } func buildBootImgGZ(out io.Writer, ctx *renderContext) (err error) { gzOut := gzip.NewWriter(out) if err = buildBootImg(gzOut, ctx); err != nil { return } gzOut.Close() return } func setupBootImage(bootImg *os.File, ctx *renderContext) (err error) { path, err := ctx.distFetch("grub-support", "1.0.0") if err != nil { return } baseImage, err := os.Open(path) if err != nil { return } defer baseImage.Close() baseImageGz, err := gzip.NewReader(baseImage) if err != nil { return } defer baseImageGz.Close() _, err = io.Copy(bootImg, baseImageGz) if err != nil { return } log.Print("running losetup...") cmd := exec.Command("losetup", "--find", "--show", "--partscan", bootImg.Name()) cmd.Stderr = os.Stderr devb, err := cmd.Output() if err != nil { return } dev := strings.TrimSpace(string(devb)) defer func() { log.Print("detaching ", dev) run("losetup", "-d", dev) }() log.Print("device: ", dev) tempDir := bootImg.Name() + ".p1.mount" err = os.Mkdir(tempDir, 0755) if err != nil { return } defer func() { log.Print("removing ", tempDir) os.RemoveAll(tempDir) }() err = syscall.Mount(dev+"p1", tempDir, "vfat", 0, "") if err != nil { return fmt.Errorf("failed to mount %s to %s: %v", dev+"p1", tempDir, err) } defer func() { log.Print("unmounting ", tempDir) syscall.Unmount(tempDir, 0) }() // add system elements tarOut, tarIn := io.Pipe() go func() { err2 := buildBootTar(tarIn, ctx) tarIn.Close() if err2 != nil { err = err2 } }() defer tarOut.Close() tarRd := tar.NewReader(tarOut) for { hdr, err := tarRd.Next() if err == io.EOF { break } if err != nil { return err } log.Print("tar: extracting ", hdr.Name) outPath := filepath.Join(tempDir, hdr.Name) os.MkdirAll(filepath.Dir(outPath), 0755) f, err := os.Create(outPath) if err != nil { return err } _, err = io.Copy(f, tarRd) f.Close() if err != nil { return err } } return } func run(program string, args ...string) (err error) { cmd := exec.Command(program, args...) cmd.Stdout = os.Stdout cmd.Stderr = os.Stderr return cmd.Run() }