package rootfs
 
 import (
 	"context"
 	"fmt"
 	"io/ioutil"
 	"os"
 
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"

 	"github.com/containerd/containerd/snapshots"

 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 )
 
 var (
 	initializers = map[string]initializerFunc{}
 )
 
 type initializerFunc func(string) error
 
 // Mounter handles mount and unmount
 type Mounter interface {
 	Mount(target string, mounts ...mount.Mount) error
 	Unmount(target string) error
 }
 
 // InitRootFS initializes the snapshot for use as a rootfs

 func InitRootFS(ctx context.Context, name string, parent digest.Digest, readonly bool, snapshotter snapshots.Snapshotter, mounter Mounter) ([]mount.Mount, error) {

 	_, err := snapshotter.Stat(ctx, name)
 	if err == nil {
 		return nil, errors.Errorf("rootfs already exists")
 	}
 	// TODO: ensure not exist error once added to snapshot package
 
 	parentS := parent.String()
 
 	initName := defaultInitializer
 	initFn := initializers[initName]
 	if initFn != nil {
 		parentS, err = createInitLayer(ctx, parentS, initName, initFn, snapshotter, mounter)
 		if err != nil {
 			return nil, err
 		}
 	}
 
 	if readonly {
 		return snapshotter.View(ctx, name, parentS)
 	}
 
 	return snapshotter.Prepare(ctx, name, parentS)
 }
 

 func createInitLayer(ctx context.Context, parent, initName string, initFn func(string) error, snapshotter snapshots.Snapshotter, mounter Mounter) (string, error) {

 	initS := fmt.Sprintf("%s %s", parent, initName)
 	if _, err := snapshotter.Stat(ctx, initS); err == nil {
 		return initS, nil
 	}
 	// TODO: ensure not exist error once added to snapshot package
 
 	// Create tempdir
 	td, err := ioutil.TempDir("", "create-init-")
 	if err != nil {
 		return "", err
 	}
 	defer os.RemoveAll(td)
 
 	mounts, err := snapshotter.Prepare(ctx, td, parent)
 	if err != nil {
 		return "", err
 	}

 	defer func() {
 		if err != nil {

 			if rerr := snapshotter.Remove(ctx, td); rerr != nil {
 				log.G(ctx).Errorf("Failed to remove snapshot %s: %v", td, rerr)
 			}

 		}
 	}()
 
 	if err = mounter.Mount(td, mounts...); err != nil {
 		return "", err
 	}
 
 	if err = initFn(td); err != nil {
 		if merr := mounter.Unmount(td); merr != nil {
 			log.G(ctx).Errorf("Failed to unmount %s: %v", td, merr)
 		}
 		return "", err
 	}
 
 	if err = mounter.Unmount(td); err != nil {
 		return "", err
 	}
 
 	if err := snapshotter.Commit(ctx, initS, td); err != nil {
 		return "", err
 	}
 
 	return initS, nil
 }