Mount syscall

package mount

import (
	"fmt"
	"os"
	"path/filepath"
	"syscall"

	diskfs "github.com/diskfs/go-diskfs"
	"github.com/diskfs/go-diskfs/partition/mbr"
	"go.uber.org/zap"
)

type Mount interface {
	Mount() error
}

type Mounter struct {
	log *zap.Logger

	mountDir  string
	mountFile string
}

func New(log *zap.Logger, mountDir, mountFile string) (*Mounter, error) {
	for _, file := range []string{mountDir, mountFile} {
		if _, err := os.Stat(file); os.IsNotExist(err) {
			return nil, err
		}
	}

	b := &Mounter{
		log:       log,
		mountDir:  mountDir,
		mountFile: mountFile,
	}

	return b, nil
}

func (m *Mounter) Mount() error {
	disk, err := diskfs.Open(m.mountFile)
	if err != nil {
		return err
	}

	var offset uint32
	var blockSize int

	// OFFSET=$((`fdisk -lu $IMAGE 2> /dev/null | grep -P "2\s+\**\s+[0-9]+\s+[0-9]+\s+[0-9]+\s+[0-9]+" | sed 's/\*//g' | awk '{print $2}'`))
	// BLOCK=$((`fdisk -lu $IMAGE 2> /dev/null | grep "^Units" | awk -F"= " '{print $2}' | awk '{print $1}'`))

	//spew.Dump(disk.Table.(*mbr.Table).Partitions)
	table := disk.Table.(*mbr.Table)
	blockSize = table.PhysicalSectorSize

	for _, partition := range table.Partitions {
		if !partition.Bootable && partition.Type == mbr.Linux {
			offset = partition.Start
		}
	}

	fullOffset := offset * uint32(blockSize)

	dst := filepath.Join(m.mountDir, "/mnt")
	err = os.MkdirAll(dst, os.ModePerm)
	if err != nil {
		return err
	}

	// sudo mount -o loop,rw,sync,offset=$(($OFFSET * $BLOCK)) $IMAGE $TMP
	opts := fmt.Sprintf("rw,sync,offset=%d", fullOffset)
	if err := syscall.Mount(m.mountFile, dst, "", syscall.MS_BIND, opts); err != nil {
		m.log.Error("Failed to bind mount subdir", zap.String("mountFile", m.mountFile), zap.String("dst", dst))
		return err
	}

	return nil
}