// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// make-fuchsia-vol is a temporarily useful script that provisions Fuchsia
// volumes based on paths provided.

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"

	"go.fuchsia.dev/fuchsia/garnet/go/src/thinfs/block/file"
	"go.fuchsia.dev/fuchsia/garnet/go/src/thinfs/fs"
	"go.fuchsia.dev/fuchsia/garnet/go/src/thinfs/fs/msdosfs"
	"go.fuchsia.dev/fuchsia/garnet/go/src/thinfs/gpt"
	"go.fuchsia.dev/fuchsia/garnet/go/src/thinfs/mbr"
)

var (
	verbose         = flag.Bool("verbose", false, "enable verbose logging")
	fuchsiaBuildDir = flag.String("fuchsia-build-dir", os.Getenv("FUCHSIA_BUILD_DIR"), "fuchsia build dir")

	bootloader = flag.String("bootloader", "", "path to bootx64.efi")
	zbi        = flag.String("zbi", "", "path to zbi (default: zircon-a from image manifests)")
	cmdline    = flag.String("cmdline", "", "path to command line file (if exists)")
	zedboot    = flag.String("zedboot", "", "path to zedboot.zbi (default: zircon-r from image manifests)")

	ramdiskOnly = flag.Bool("ramdisk-only", false, "ramdisk-only mode - only write an ESP partition")
	blob        = flag.String("blob", "", "path to blob partition image (not used with ramdisk)")
	data        = flag.String("data", "", "path to data partition image (not used with ramdisk)")

	abr        = flag.Bool("abr", true, "add Zircon-{A,B,R} partitions")
	zirconA    = flag.String("zirconA", "", "path to partition image for Zircon-A (default: from -zbi)")
	vbmetaA    = flag.String("vbmetaA", "", "path to partition image for Vbmeta-A")
	zirconB    = flag.String("zirconB", "", "path to partition image for Zircon-B (default: from -zbi)")
	vbmetaB    = flag.String("vbmetaB", "", "path to partition image for Vbmeta-B")
	zirconR    = flag.String("zirconR", "", "path to partition image for Zircon-R (default: zircon-r from image manifests)")
	vbmetaR    = flag.String("vbmetaR", "", "path to partition image for Vbmeta-R")
	abrSize    = flag.Int64("abr-size", 256*1024*1024, "Kernel partition size for A/B/R")
	vbmetaSize = flag.Int64("vbmeta-size", 8*1024, "partition size for vbmeta A/B/R")
	abrBoot    = flag.String("abr-boot", "a", "A/B/R partition to boot by default")

	blockSize           = flag.Int64("block-size", 0, "the block size of the target disk (0 means detect)")
	physicalBlockSize   = flag.Int64("physical-block-size", 0, "the physical block size of the target disk (0 means detect)")
	optimalTransferSize = flag.Int64("optimal-transfer-size", 0, "the optimal transfer size of the target disk (0 means unknown/unused)")

	efiSize = flag.Int64("efi-size", 63*1024*1024, "efi partition size in bytes")
	fvmSize = flag.Int64("fvm-size", 0, "fvm partition size in bytes (0 means `fill`)")
	resize  = flag.Int64("resize", 0, "create or resize the image to this size in bytes")
)

// imageManifest is basename of the image manifest file.
const imageManifest = "images.json"

type imageManifestEntry struct {
	Name string `json:"name"`
	Path string `json:"path"`
	Type string `json:"type"`
}

// imagePaths contains the default image paths that are produced by a build manifest, populated by tryLoadManifests.
var imagePaths = map[string]string{}

// getImage fetches an image by name or exits fatally
func getImage(name string) string {
	if path, ok := imagePaths[name]; ok {
		return path
	}
	log.Fatalf("Missing image path: %q cannot continue", name)
	return ""
}

func init() {
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: %s disk-path\n", filepath.Base(os.Args[0]))
		flag.PrintDefaults()
	}
}

func tryLoadManifests() {
	if *fuchsiaBuildDir == "" {
		return
	}
	f, err := os.Open(filepath.Join(*fuchsiaBuildDir, imageManifest))
	if err != nil {
		log.Printf("warning: failed to load %s: %v", imageManifest, err)
		return
	}
	defer f.Close()

	var entries []imageManifestEntry
	if err := json.NewDecoder(f).Decode(&entries); err != nil {
		log.Printf("warning: failed to load %s: %v", imageManifest, err)
		return
	}

	for _, image := range entries {
		imagePaths[image.Type+"_"+image.Name] = image.Path
	}
}

func needFuchsiaBuildDir() {
	if *fuchsiaBuildDir == "" {
		log.Fatalf("either pass -fuchsia-build-dir or set $FUCHSIA_BUILD_DIR")
	}
}

func main() {
	flag.Parse()
	tryLoadManifests()

	if *bootloader == "" {
		needFuchsiaBuildDir()
		*bootloader = filepath.Join(*fuchsiaBuildDir, "efi_x64/bootx64.efi")
	}
	if _, err := os.Stat(*bootloader); err != nil {
		log.Fatalf("cannot read %q: %s", *bootloader, err)
	}

	if *zbi == "" {
		needFuchsiaBuildDir()
		*zbi = filepath.Join(*fuchsiaBuildDir, getImage("zbi_zircon-a"))
	}
	if _, err := os.Stat(*zbi); err != nil {
		log.Fatalf("cannot read %q: %s", *zbi, err)
	}

	if *zedboot == "" {
		needFuchsiaBuildDir()
		*zedboot = filepath.Join(*fuchsiaBuildDir, getImage("zbi_zircon-r"))
	}
	if _, err := os.Stat(*zedboot); err != nil {
		log.Fatalf("cannot read %q: %s", *zedboot, err)
	}

	if *cmdline == "" {
		needFuchsiaBuildDir()
		p := filepath.Join(*fuchsiaBuildDir, "cmdline")
		if _, err := os.Stat(p); err == nil {
			*cmdline = p
		}
	} else {
		if _, err := os.Stat(*cmdline); err != nil {
			log.Fatal(err)
		}
	}

	bootMode := BOOT_A
	if *abr {
		if *zirconA == "" {
			needFuchsiaBuildDir()
			*zirconA = *zbi
		}
		if *vbmetaA == "" {
			*vbmetaA = filepath.Join(*fuchsiaBuildDir, getImage("vbmeta_zircon-a"))
		}
		if *zirconB == "" {
			*zirconB = *zbi
		}
		if *vbmetaB == "" {
			*vbmetaB = filepath.Join(*fuchsiaBuildDir, getImage("vbmeta_zircon-a"))
		}
		if *zirconR == "" {
			*zirconR = filepath.Join(*fuchsiaBuildDir, getImage("zbi_zircon-r"))
		}
		if *vbmetaR == "" {
			*vbmetaR = filepath.Join(*fuchsiaBuildDir, getImage("vbmeta_zircon-r"))
		}

		switch strings.ToLower(*abrBoot) {
		case "a":
			bootMode = BOOT_A
		case "b":
			bootMode = BOOT_B
		case "r":
			bootMode = BOOT_RECOVERY
		default:
			log.Fatalf("Invalid -abr-boot passed: expected 'a', 'b', or 'r'.")
		}
	}

	if !*ramdiskOnly {
		if *blob == "" {
			needFuchsiaBuildDir()
			*blob = filepath.Join(*fuchsiaBuildDir, getImage("blk_blob"))
		}
		if *data == "" {
			needFuchsiaBuildDir()
			*data = filepath.Join(*fuchsiaBuildDir, getImage("blk_data"))
		}

		if _, err := os.Stat(*blob); err != nil {
			log.Fatalf("Blob image error: %s\nEither provide a blob image, or pass -ramdisk-only", err)
		}
		if _, err := os.Stat(*data); err != nil {
			log.Fatalf("Data image error: %s\nEither provide a data image, or pass -ramdisk-only", err)
		}
	}

	if len(flag.Args()) != 1 {
		flag.Usage()
		os.Exit(1)
	}

	disk, err := filepath.Abs(flag.Args()[0])
	if err != nil {
		log.Fatal(err)
	}

	if *resize != 0 {
		s, err := os.Stat(disk)
		if err == nil {
			if s.Size() != *resize {
				if *verbose {
					log.Printf("Resizing %q from %d to %d", disk, s.Size(), *resize)
				}
				if err := os.Truncate(disk, *resize); err != nil {
					log.Fatalf("failed to truncate %q to %d: %s", disk, *resize, err)
				}
			}
		} else if os.IsNotExist(err) {
			if *verbose {
				log.Printf("Creating %q", disk)
			}
			f, err := os.Create(disk)
			if err != nil {
				log.Fatalf("failed to create %q: %s", disk, err)
			}
			if err := f.Truncate(*resize); err != nil {
				log.Fatalf("failed to truncate %q to %d: %s", disk, *resize, err)
			}
			f.Close()
		} else {
			log.Fatal(err)
		}
	} else {
		if _, err := os.Stat(disk); err != nil {
			log.Fatalf("cannot read %q: %s\n", disk, err)
		}
	}

	f, err := os.Open(disk)
	if err != nil {
		log.Fatal(err)
	}

	if *blockSize == 0 {
		lbs, err := gpt.GetLogicalBlockSize(f)
		if err != nil {
			log.Printf("WARNING: could not detect logical block size: %s. Assuming %d\n", err, lbs)
		}
		*blockSize = int64(lbs)
	}

	if *physicalBlockSize == 0 {
		pbs, err := gpt.GetPhysicalBlockSize(f)
		if err != nil {
			log.Printf("WARNING: could not detect physical block size: %s. Assuming %d\n", err, pbs)
		}
		*physicalBlockSize = int64(pbs)
	}
	if *physicalBlockSize < 4096 && runtime.GOOS == "darwin" {
		// OSX is not reliably returning correct values for USB sticks, unclear why
		*physicalBlockSize = 4096
	}

	var (
		logical  = uint64(*blockSize)
		physical = uint64(*physicalBlockSize)
		optimal  = uint64(*optimalTransferSize)

		diskSize uint64
	)

	// ignore the error here as it may be an image file...
	diskSize, _ = gpt.GetDiskSize(f)

	if diskSize == 0 {
		s, err := os.Stat(disk)
		if err != nil {
			log.Fatalf("could not stat %q: %s\n", disk, err)
		}
		diskSize = uint64(s.Size())
	}
	if diskSize == 0 {
		log.Fatalf("could not determine size of %q", disk)
	}

	// Note: this isn't entirely correct, as it doesn't take into account padding.
	// Consider adding a real API for this in the GPT lib.
	minGPTSize := int64((gpt.MinPartitionEntryArraySize + gpt.HeaderSize) * 2)
	if uint64(*efiSize+minGPTSize) > diskSize {
		log.Fatalf("%q is not large enough for the partition layout\n", disk)
	}

	if *verbose {
		log.Printf("Disk: %s", disk)
		log.Printf("Disk size: %d", diskSize)
		log.Printf("Block Size: %d", logical)
		log.Printf("Physical block size: %d", physical)
		log.Printf("Optimal transfer size: %d", optimal)
	}

	g, err := gpt.ReadGPT(f, logical, diskSize)
	if err != nil {
		log.Fatal(err)
	}

	lbaSize := diskSize / logical
	g.MBR = mbr.NewProtectiveMBR(lbaSize)
	g.Primary.Partitions = []gpt.PartitionEntry{}

	g.Update(logical, physical, optimal, diskSize) // for the firstusablelba
	end := g.Primary.FirstUsableLBA

	var efiStart uint64
	efiStart, end = optimalBlockAlign(end, uint64(*efiSize), logical, physical, optimal)
	// compute the size of the fat geometry that fits within the well-aligned GPT
	// partition that was computed above.
	*efiSize = fitFAT(int64((end-1)-efiStart) * int64(logical))
	// efiEnd is the last sector of viable fat geometry, which may be different
	// from end, which is the last sector of the gpt partition.
	efiEnd := efiStart + (uint64(*efiSize) / logical) - 1

	if *verbose {
		log.Printf("EFI START: %d", efiStart)
		log.Printf("EFI END: %d", efiEnd)
		log.Printf("EFI LB SIZE: %d", efiEnd-efiStart+1)
	}

	g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
		PartitionTypeGUID:   gpt.GUIDEFI,
		UniquePartitionGUID: gpt.NewRandomGUID(),
		PartitionName:       gpt.NewPartitionName("efi-system"),
		StartingLBA:         efiStart,
		EndingLBA:           end,
	})

	var startingCHS [3]byte
	startingCHS[0] = byte(efiStart / (16 * 63))
	startingCHS[1] = byte((efiStart / 63) % 16)
	startingCHS[2] = byte((efiStart % 63) + 1)

	var endingCHS [3]byte
	endingCHS[0] = byte(efiEnd / (16 * 63))
	endingCHS[1] = byte((efiEnd / 63) % 16)
	endingCHS[2] = byte((efiEnd % 63) + 1)

	// Install a "hybrid MBR" hack for the case of bios bootloaders that might
	// need it (e.g. rpi's binary blob that's stuck in MBR land).
	g.MBR.PartitionRecord[2] = mbr.PartitionRecord{
		BootIndicator: 0x80,
		StartingCHS:   startingCHS,
		EndingCHS:     endingCHS,
		OSType:        mbr.FAT32,
		StartingLBA:   uint32(efiStart),
		SizeInLBA:     uint32(efiEnd),
	}

	var aStart, bStart, rStart uint64
	var vbmetaAStart, vbmetaBStart, vbmetaRStart, miscStart uint64
	if *abr {
		aStart, end = optimalBlockAlign(end, uint64(*abrSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaZirconA,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("ZIRCON-A"),
			StartingLBA:         aStart,
			EndingLBA:           end,
		})

		vbmetaAStart, end = optimalBlockAlign(end, uint64(*vbmetaSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaVbmetaA,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("VBMETA_A"),
			StartingLBA:         vbmetaAStart,
			EndingLBA:           end,
		})

		bStart, end = optimalBlockAlign(end, uint64(*abrSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaZirconB,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("ZIRCON-B"),
			StartingLBA:         bStart,
			EndingLBA:           end,
		})

		vbmetaBStart, end = optimalBlockAlign(end, uint64(*vbmetaSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaVbmetaB,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("VBMETA_B"),
			StartingLBA:         vbmetaBStart,
			EndingLBA:           end,
		})

		rStart, end = optimalBlockAlign(end, uint64(*abrSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaZirconR,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("ZIRCON-R"),
			StartingLBA:         rStart,
			EndingLBA:           end,
		})

		vbmetaRStart, end = optimalBlockAlign(end, uint64(*vbmetaSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaVbmetaR,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("VBMETA_R"),
			StartingLBA:         vbmetaRStart,
			EndingLBA:           end,
		})

		miscStart, end = optimalBlockAlign(end, uint64(*vbmetaSize), logical, physical, optimal)
		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaMisc,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("MISC"),
			StartingLBA:         miscStart,
			EndingLBA:           end,
		})
	}

	var fvmStart uint64

	fvmStart, end = optimalBlockAlign(end+1, uint64(*fvmSize), logical, physical, optimal)
	if !*ramdiskOnly {
		if *fvmSize == 0 {
			end = g.Primary.LastUsableLBA
		}
		*fvmSize = int64((end - fvmStart) * logical)

		g.Primary.Partitions = append(g.Primary.Partitions, gpt.PartitionEntry{
			PartitionTypeGUID:   gpt.GUIDFuchsiaFVM,
			UniquePartitionGUID: gpt.NewRandomGUID(),
			PartitionName:       gpt.NewPartitionName("FVM"),
			StartingLBA:         fvmStart,
			EndingLBA:           end,
		})
	}

	g.Update(logical, physical, optimal, diskSize)

	if err := g.Validate(); err != nil {
		log.Fatal(err)
	}

	if *verbose {
		log.Printf("EFI size: %d", *efiSize)
		if !*ramdiskOnly {
			log.Printf("FVM size: %d", *fvmSize)
		}

		log.Printf("Writing GPT")
	}

	f, err = os.OpenFile(disk, os.O_RDWR, 0750)
	if err != nil {
		log.Fatal(err)
	}
	if _, err := g.WriteTo(f); err != nil {
		log.Fatalf("error writing partition table: %s", err)
	}

	f.Sync()

	aStart = aStart * logical
	vbmetaAStart = vbmetaAStart * logical
	bStart = bStart * logical
	vbmetaBStart = vbmetaBStart * logical
	rStart = rStart * logical
	vbmetaRStart = vbmetaRStart * logical
	miscStart = miscStart * logical
	efiStart = efiStart * logical
	fvmStart = fvmStart * logical

	if *verbose {
		log.Printf("Writing EFI partition and files")
	}

	cmd := exec.Command(fuchsiaTool("mkfs-msdosfs"),
		"-@", strconv.FormatUint(efiStart, 10),
		// XXX(raggi): mkfs-msdosfs offset gets subtracted by the tool for available
		// size, so we have to add the offset back on to get the correct geometry.
		"-S", strconv.FormatUint(uint64(*efiSize)+efiStart, 10),
		"-F", "32",
		"-L", "ESP",
		"-O", "Fuchsia",
		"-b", fmt.Sprintf("%d", logical),
		disk,
	)

	if out, err := cmd.CombinedOutput(); err != nil {
		log.Printf("mkfs-msdosfs failed:\n%s", out)
		log.Fatal(err)
	}

	dev, err := file.NewRange(f, int64(logical), int64(efiStart), *efiSize)
	if err != nil {
		log.Fatal(err)
	}

	fatfs, err := msdosfs.New(disk, dev, fs.ReadWrite|fs.Force)
	if err != nil {
		log.Fatal(err)
	}

	root := fatfs.RootDirectory()

	tf, err := ioutil.TempFile("", "gsetup-boot")
	if err != nil {
		log.Fatal(err)
	}
	tf.WriteString("efi\\boot\\bootx64.efi")
	tf.Close()
	defer os.Remove(tf.Name())

	msCopyIn(root, tf.Name(), "EFI/Google/GSetup/Boot")
	msCopyIn(root, *bootloader, "EFI/BOOT/bootx64.efi")
	if !*abr {
		msCopyIn(root, *zbi, "zircon.bin")
		msCopyIn(root, *zedboot, "zedboot.bin")
	}
	if *cmdline != "" {
		msCopyIn(root, *cmdline, "cmdline")
	}

	root.Sync()
	if err := root.Close(); err != nil {
		log.Fatal(err)
	}
	if err := fatfs.Close(); err != nil {
		log.Fatal(err)
	}

	f.Sync()

	if *abr {
		if *verbose {
			log.Print("Populating A/B/R and vbmeta partitions")
		}
		partitionCopy(f, int64(aStart), *abrSize, *zirconA)
		partitionCopy(f, int64(vbmetaAStart), *vbmetaSize, *vbmetaA)
		partitionCopy(f, int64(bStart), *abrSize, *zirconB)
		partitionCopy(f, int64(vbmetaBStart), *vbmetaSize, *vbmetaB)
		partitionCopy(f, int64(rStart), *abrSize, *zirconR)
		partitionCopy(f, int64(vbmetaRStart), *vbmetaSize, *vbmetaR)
		if _, err := f.Seek(int64(miscStart), os.SEEK_SET); err != nil {
			log.Fatal(err)
		}
		if err := WriteAbr(bootMode, f); err != nil {
			log.Fatal(err)
		}

	}

	f.Sync()

	if !*ramdiskOnly {
		if *verbose {
			log.Print("Populating FVM in GPT image")
		}
		fvm(disk, int64(fvmStart), *fvmSize, "create", "--blob", *blob, "--data", *data)
	}

	// Keep the file open so that OSX doesn't try to remount the disk while tools are working on it.
	if err := f.Close(); err != nil {
		log.Fatal(err)
	}

	if *verbose {
		log.Printf("Done")
	}
}

func partitionCopy(f *os.File, start, size int64, path string) {
	input, err := os.Open(path)
	if err != nil {
		log.Fatalf("partition copy failed for input: %s: %s", path, err)
	}
	defer input.Close()
	input_info, err := input.Stat()
	if err != nil {
		log.Fatalf("stat failed for input: %s: %s", path, err)
	}
	if input_info.Size() > size {
		log.Printf("WARNING: %s is larger than the provided ABR size", path)
	}
	r := io.LimitReader(input, size)
	if _, err := f.Seek(start, os.SEEK_SET); err != nil {
		log.Fatalf("partition copy failed for input: %s: %s", path, err)
	}
	_, err = io.Copy(f, r)
	if err != nil {
		log.Fatalf("partition copy failed for input: %s: %s", path, err)
	}
}

func fvm(disk string, offset, size int64, command string, args ...string) {
	offs := strconv.FormatInt(offset, 10)
	szs := strconv.FormatInt(size, 10)
	argv := []string{disk, command, "--offset", offs, "--length", szs}
	argv = append(argv, args...)
	cmd := exec.Command(fuchsiaTool("fvm"), argv...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	if err := cmd.Run(); err != nil {
		log.Fatalf("fvm %s failed", argv)
	}
}

// msCopyIn copies src from the host filesystem into dst under the given
// msdosfs root.
func msCopyIn(root fs.Directory, src, dst string) {
	d := root
	defer d.Sync()

	dStack := []fs.Directory{}

	defer func() {
		for _, d := range dStack {
			d.Sync()
			d.Close()
		}
	}()

	destdir := filepath.Dir(dst)
	name := filepath.Base(dst)

	for _, part := range strings.Split(destdir, "/") {
		if part == "." {
			continue
		}

		var err error
		_, d, _, err = d.Open(part, fs.OpenFlagRead|fs.OpenFlagCreate|fs.OpenFlagDirectory)
		if err != nil {
			log.Fatalf("open/create %s: %#v %s", part, err, err)
		}
		d.Sync()
		dStack = append(dStack, d)
	}

	to, _, _, err := d.Open(name, fs.OpenFlagWrite|fs.OpenFlagCreate|fs.OpenFlagFile)
	if err != nil {
		log.Fatalf("creating %s in msdosfs: %s", name, err)
	}
	defer to.Close()

	from, err := os.Open(src)
	if err != nil {
		log.Fatal(err)
	}
	defer from.Close()

	b := make([]byte, 4096)
	for err == nil {
		var n int
		n, err = from.Read(b)
		if n > 0 {
			if _, err := to.Write(b[:n], 0, fs.WhenceFromCurrent); err != nil {
				log.Fatalf("writing %s to msdosfs file: %s", name, err)
			}
		}
	}
	to.Sync()
	if err != nil && err != io.EOF {
		log.Fatal(err)
	}
}

// optimalBlockAlign computes a start and end logical block address for a
// partition that starts at or after first (block address), of size byteSize,
// for a disk with logical, physical and optimal byte sizes. It returns the
// start and end block addresses.
func optimalBlockAlign(first, byteSize, logical, physical, optimal uint64) (start, end uint64) {
	var alignTo = logical
	if physical > alignTo {
		alignTo = physical
	}
	if optimal > alignTo {
		alignTo = optimal
	}

	lAlign := alignTo / logical

	if d := first % lAlign; d != 0 {
		start = first + lAlign - d
	}

	lSize := byteSize / logical
	if byteSize%logical == 0 {
		lSize++
	}

	end = start + lSize
	return
}

func fuchsiaTool(name string) string {
	var tool string
	tool, _ = exec.LookPath(name)
	if tool == "" {
		needFuchsiaBuildDir()
		tool, _ = exec.LookPath(filepath.Join(*fuchsiaBuildDir, "host_x64", name))
	}
	if tool == "" {
		log.Fatalf("Could not find %q, you might need to build fuchsia", name)
	}
	return tool
}

// sectors per track is 63, and a sector is 512, so we must round to the nearest
// 32256.
const sizeAlignment = 32256

// N.B. fitFAT shrinks, not grows, as it intends to identify the nearest
// FAT-compatible geometry that fits inside of "total".
func fitFAT(total int64) int64 {
	if d := total % sizeAlignment; d != 0 {
		total = total - d
	}
	return total
}