//	清除thin pool

1.1 func (d *Driver) Cleanup() error {

	// 停止thin pool

	err := d.DeviceSet.Shutdown()

	return err

}

//	当载入新镜像时，加入一个新thin device

//	id为containerid或imageid

1.2 func (d *Driver) Create(id, parent string) error {

	if err := d.DeviceSet.AddDevice(id, parent); err != nil {

		return err

	}

	return nil

}

//	删除thin device

1.3 func (d *Driver) Remove(id string) error {

	//检查thin device是否存在

	if !d.DeviceSet.HasDevice(id) {

		return nil

	}

	//通过id从thin pool中删除设备

	if err := d.DeviceSet.DeleteDevice(id); err != nil {

		return err

	}

	//mp为/var/lib/docker/devicemapper/mnt/$id

	mp := path.Join(d.home, "mnt", id)

	//删除文件夹下全部的文件

	if err := os.RemoveAll(mp); err != nil && !os.IsNotExist(err) {

		return err

	}

	return nil

}

//	挂载thin device到/var/lib/docker/devicemapper/mnt/$id文件夹下

1.4 func (d *Driver) Get(id, mountLabel string) (string, error) {

	//mp=/var/lib/docker/devicemapper/mnt/$id

	mp := path.Join(d.home, "mnt", id)

	//创建文件夹/var/lib/docker/devicemapper/mnt/$id

	if err := os.MkdirAll(mp, 0755); err != nil && !os.IsExist(err) {

		return "", err

	}

	//挂载thin device到/var/lib/docker/devicemapper/mnt/$id

	if err := d.DeviceSet.MountDevice(id, mp, mountLabel); err != nil {

		return "", err

	}

	//创建rootfs到/var/lib/docker/devicemapper/mnt/$id/rootfs

	rootFs := path.Join(mp, "rootfs")

	if err := os.MkdirAll(rootFs, 0755); err != nil && !os.IsExist(err) {

		d.DeviceSet.UnmountDevice(id)

		return "", err

	}

	//创建id

	idFile := path.Join(mp, "id")

	if _, err := os.Stat(idFile); err != nil && os.IsNotExist(err) {

		if err := ioutil.WriteFile(idFile, []byte(id), 0600); err != nil {

			d.DeviceSet.UnmountDevice(id)

			return "", err

		}

	}

	//返回/var/lib/docker/devicemapper/mnt/$id/rootfs文件夹

	return rootFs, nil

}

//	从/var/lib/docker/devicemapper/mnt/$id下解挂设备

1.5 func (d *Driver) Put(id string) {

	if err := d.DeviceSet.UnmountDevice(id); err != nil {

		utils.Errorf("Warning: error unmounting device %s: %s\n", id, err)

	}

}

//	推断$id所相应的设备是否存在

1.6 func (d *Driver) Exists(id string) bool {

	return d.DeviceSet.HasDevice(id)

}