Cannot create partition at end of disk then make directory about go-diskfs HOT 22 CLOSED

package main

import (
	"fmt"
	"log"
	"os"
	"path"
	"strconv"

	diskfs "github.com/diskfs/go-diskfs"
	"github.com/diskfs/go-diskfs/disk"
	"github.com/diskfs/go-diskfs/filesystem"
	"github.com/diskfs/go-diskfs/partition/mbr"
)

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func CreateFSAndDir(diskImg string, partSize int) int64 {
	if diskImg == "" {
		log.Fatal("must have a valid path for diskImg")
	}
	mydisk, err := diskfs.Open(diskImg)
	if err != nil {
		var diskSize int64
		diskSize = 5 * 1024 * 1024 * 1024 // 5 GB
		mydisk, err = diskfs.Create(diskImg, diskSize, diskfs.Raw)
		check(err)
	}

	cloudInitSize := partSize * 1024 * 1024 * 1024 // 1 GB
	cloudInitSectors := uint32(cloudInitSize / 512)
	// we want to create it at the end of the disk
	// so find the disk sector count and minus the cloudinit sectors
	cloudInitStart := uint32(int(mydisk.Size)/512) - cloudInitSectors

	table := &mbr.Table{
		LogicalSectorSize:  512,
		PhysicalSectorSize: 512,
		Partitions: []*mbr.Partition{
			{
				Bootable: false,
				Type:     mbr.Linux,
				Start:    cloudInitStart,
				Size:     cloudInitSectors,
			},
		},
	}

	log.Print("Writing partition table to disk")
	err = mydisk.Partition(table)
	check(err)

	fspec := disk.FilesystemSpec{Partition: 1, FSType: filesystem.TypeFat32, VolumeLabel: "config-2"}
	fs, err := mydisk.CreateFilesystem(fspec)
	check(err)

	cloudInitPrefix := path.Join("/", "openstack", "latest")
	// place down cloud-init info
	log.Print("Creating cloud init directory structure")
	err = fs.Mkdir(cloudInitPrefix)
	if err != nil {
		log.Fatalf("Error creating cloud init directory structure: %v", err)
	}
	return int64(cloudInitStart)*512
}

func main() {
	if len(os.Args) < 3 {
		fmt.Printf("Usage: %s <outfile> <partition size in GB>\n", os.Args[0])
		fmt.Printf("Example: %s ./foo.img 2\n", os.Args[0])
		os.Exit(1)
	}
	i, err := strconv.Atoi(os.Args[2])
	if err != nil {
		fmt.Printf("second argument *must* be an integer, you gave %s: %v", os.Args[1], err)
		os.Exit(1)
	}

	start := CreateFSAndDir(os.Args[1], i)
	fmt.Printf("fat32 partition starts at byte %d\n", start)
}

package main

import (
	"fmt"
	"log"
	"os"
	"path"
	"strconv"

	diskfs "github.com/diskfs/go-diskfs"
	"github.com/diskfs/go-diskfs/disk"
	"github.com/diskfs/go-diskfs/filesystem"
	"github.com/diskfs/go-diskfs/partition/mbr"
)

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func CreateFSAndDir(diskImg string, partSize int) int64 {
	if diskImg == "" {
		log.Fatal("must have a valid path for diskImg")
	}
	mydisk, err := diskfs.Open(diskImg)
	if err != nil {
		var diskSize int64
		diskSize = 5 * 1024 * 1024 * 1024 // 5 GB
		mydisk, err = diskfs.Create(diskImg, diskSize, diskfs.Raw)
		check(err)
	}

	cloudInitSize := partSize * 1024 * 1024 * 1024 // 1 GB
	cloudInitSectors := uint32(cloudInitSize / 512)
	// we want to create it at the end of the disk
	// so find the disk sector count and minus the cloudinit sectors
	cloudInitStart := uint32(int(mydisk.Size)/512) - cloudInitSectors

	table := &mbr.Table{
		LogicalSectorSize:  512,
		PhysicalSectorSize: 512,
		Partitions: []*mbr.Partition{
			{
				Bootable: false,
				Type:     mbr.Linux,
				Start:    cloudInitStart,
				Size:     cloudInitSectors,
			},
		},
	}

	log.Print("Writing partition table to disk")
	err = mydisk.Partition(table)
	check(err)

	fspec := disk.FilesystemSpec{Partition: 1, FSType: filesystem.TypeFat32, VolumeLabel: "config-2"}
	fs, err := mydisk.CreateFilesystem(fspec)
	check(err)

	cloudInitPrefix := path.Join("/", "openstack", "latest")
	// place down cloud-init info
	log.Print("Creating cloud init directory structure")
	err = fs.Mkdir(cloudInitPrefix)
	if err != nil {
		log.Fatalf("Error creating cloud init directory structure: %v", err)
	}
	return int64(cloudInitStart)*512
}

func ReadRootDir(diskImg string) []os.FileInfo {
	disk, err := diskfs.Open(diskImg)
	if err != nil {
		log.Panic(err)
	}
	table, err := disk.GetPartitionTable()
	if err != nil {
		log.Panic(err)
	}
	disk.Table = table
	fs, err := disk.GetFilesystem(1)
	if err != nil {
		log.Panic(err)
	}
	files, err := fs.ReadDir("/")
	if err != nil {
		log.Panic(err)
	}
	return files

}

func main() {
	if len(os.Args) < 3 {
		fmt.Printf("Usage: %s <outfile> <partition size in GB>\n", os.Args[0])
		fmt.Printf("Example: %s ./foo.img 2\n", os.Args[0])
		os.Exit(1)
	}
	i, err := strconv.Atoi(os.Args[2])
	if err != nil {
		fmt.Printf("second argument *must* be an integer, you gave %s: %v", os.Args[1], err)
		os.Exit(1)
	}

	start := CreateFSAndDir(os.Args[1], i)
	fmt.Printf("fat32 partition starts at byte %d\n", start)
	root := ReadRootDir(os.Args[1])
	fmt.Printf("%#v\n", root)
}