@@ -23,6 +23,7 @@ import (

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/layer"

 	"github.com/docker/docker/pkg/idtools"

+	"github.com/docker/docker/pkg/ioutils"

 	"github.com/docker/docker/pkg/promise"

 	"github.com/docker/docker/pkg/signal"

 	"github.com/docker/docker/pkg/symlink"

@@ -131,7 +132,7 @@ func (container *Container) ToDisk() error {

 		return err

 	}

-	jsonSource, err := os.Create(pth)

+	jsonSource, err := ioutils.NewAtomicFileWriter(pth, 0666)

 	if err != nil {

 		return err

 	}

@@ -191,7 +192,7 @@ func (container *Container) WriteHostConfig() error {

 		return err

 	}

-	f, err := os.Create(pth)

+	f, err := ioutils.NewAtomicFileWriter(pth, 0666)

 	if err != nil {

 		return err

 	}

@@ -5,6 +5,8 @@ import (

 	"os"

 	"path/filepath"

 	"sync"

+

+	"github.com/docker/docker/pkg/ioutils"

 )

 // Store implements a K/V store for mapping distribution-related IDs

@@ -56,14 +58,10 @@ func (store *FSMetadataStore) Set(namespace, key string, value []byte) error {

 	defer store.Unlock()

 	path := store.path(namespace, key)

-	tempFilePath := path + ".tmp"

 	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {

 		return err

 	}

-	if err := ioutil.WriteFile(tempFilePath, value, 0644); err != nil {

-		return err

-	}

-	return os.Rename(tempFilePath, path)

+	return ioutils.AtomicWriteFile(path, value, 0644)

 }

 // Delete removes data indexed by namespace and key. The data file named after

@@ -9,6 +9,7 @@ import (

 	"github.com/Sirupsen/logrus"

 	"github.com/docker/distribution/digest"

+	"github.com/docker/docker/pkg/ioutils"

 )

 // IDWalkFunc is function called by StoreBackend.Walk

@@ -118,12 +119,7 @@ func (s *fs) Set(data []byte) (ID, error) {

 	}

 	id := ID(digest.FromBytes(data))

-	filePath := s.contentFile(id)

-	tempFilePath := s.contentFile(id) + ".tmp"

-	if err := ioutil.WriteFile(tempFilePath, data, 0600); err != nil {

-		return "", err

-	}

-	if err := os.Rename(tempFilePath, filePath); err != nil {

+	if err := ioutils.AtomicWriteFile(s.contentFile(id), data, 0600); err != nil {

 		return "", err

 	}

@@ -156,12 +152,7 @@ func (s *fs) SetMetadata(id ID, key string, data []byte) error {

 	if err := os.MkdirAll(baseDir, 0700); err != nil {

 		return err

 	}

-	filePath := filepath.Join(s.metadataDir(id), key)

-	tempFilePath := filePath + ".tmp"

-	if err := ioutil.WriteFile(tempFilePath, data, 0600); err != nil {

-		return err

-	}

-	return os.Rename(tempFilePath, filePath)

+	return ioutils.AtomicWriteFile(filepath.Join(s.metadataDir(id), key), data, 0600)

 }

 // GetMetadata returns metadata for a given ID.

@@ -19,6 +19,7 @@ import (

 	"github.com/docker/docker/image"

 	imagev1 "github.com/docker/docker/image/v1"

 	"github.com/docker/docker/layer"

+	"github.com/docker/docker/pkg/ioutils"

 	"github.com/docker/docker/reference"

 )

@@ -160,12 +161,7 @@ func calculateLayerChecksum(graphDir, id string, ls checksumCalculator) error {

 		return err

 	}

-	tmpFile := filepath.Join(graphDir, id, migrationDiffIDFileName+".tmp")

-	if err := ioutil.WriteFile(tmpFile, []byte(diffID), 0600); err != nil {

-		return err

-	}

-

-	if err := os.Rename(tmpFile, filepath.Join(graphDir, id, migrationDiffIDFileName)); err != nil {

+	if err := ioutils.AtomicWriteFile(filepath.Join(graphDir, id, migrationDiffIDFileName), []byte(diffID), 0600); err != nil {

 		return err

 	}

new file mode 100644

@@ -0,0 +1,75 @@

+package ioutils

+

+import (

+	"io"

+	"io/ioutil"

+	"os"

+	"path/filepath"

+)

+

+// NewAtomicFileWriter returns WriteCloser so that writing to it writes to a

+// temporary file and closing it atomically changes the temporary file to

+// destination path. Writing and closing concurrently is not allowed.

+func NewAtomicFileWriter(filename string, perm os.FileMode) (io.WriteCloser, error) {

+	f, err := ioutil.TempFile(filepath.Dir(filename), ".tmp-"+filepath.Base(filename))

+	if err != nil {

+		return nil, err

+	}

+	abspath, err := filepath.Abs(filename)

+	if err != nil {

+		return nil, err

+	}

+	return &atomicFileWriter{

+		f:  f,

+		fn: abspath,

+	}, nil

+}

+

+// AtomicWriteFile atomically writes data to a file named by filename.

+func AtomicWriteFile(filename string, data []byte, perm os.FileMode) error {

+	f, err := NewAtomicFileWriter(filename, perm)

+	if err != nil {

+		return err

+	}

+	n, err := f.Write(data)

+	if err == nil && n < len(data) {

+		err = io.ErrShortWrite

+	}

+	if err1 := f.Close(); err == nil {

+		err = err1

+	}

+	return err

+}

+

+type atomicFileWriter struct {

+	f        *os.File

+	fn       string

+	writeErr error

+}

+

+func (w *atomicFileWriter) Write(dt []byte) (int, error) {

+	n, err := w.f.Write(dt)

+	if err != nil {

+		w.writeErr = err

+	}

+	return n, err

+}

+

+func (w *atomicFileWriter) Close() (retErr error) {

+	defer func() {

+		if retErr != nil {

+			os.Remove(w.f.Name())

+		}

+	}()

+	if err := w.f.Sync(); err != nil {

+		w.f.Close()

+		return err

+	}

+	if err := w.f.Close(); err != nil {

+		return err

+	}

+	if w.writeErr == nil {

+		return os.Rename(w.f.Name(), w.fn)

+	}

+	return nil

+}

new file mode 100644

@@ -0,0 +1,31 @@

+package ioutils

+

+import (

+	"bytes"

+	"io/ioutil"

+	"os"

+	"path/filepath"

+	"testing"

+)

+

+func TestAtomicWriteToFile(t *testing.T) {

+	tmpDir, err := ioutil.TempDir("", "atomic-writers-test")

+	if err != nil {

+		t.Fatalf("Error when creating temporary directory: %s", err)

+	}

+	defer os.RemoveAll(tmpDir)

+

+	expected := []byte("barbaz")

+	if err := AtomicWriteFile(filepath.Join(tmpDir, "foo"), expected, 0600); err != nil {

+		t.Fatalf("Error writing to file: %v", err)

+	}

+

+	actual, err := ioutil.ReadFile(filepath.Join(tmpDir, "foo"))

+	if err != nil {

+		t.Fatalf("Error reading from file: %v", err)

+	}

+

+	if bytes.Compare(actual, expected) != 0 {

+		t.Fatalf("Data mismatch, expected %q, got %q", expected, actual)

+	}

+}

@@ -4,7 +4,6 @@ import (

 	"encoding/json"

 	"errors"

 	"fmt"

-	"io/ioutil"

 	"os"

 	"path/filepath"

 	"sort"

@@ -12,6 +11,7 @@ import (

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/image"

+	"github.com/docker/docker/pkg/ioutils"

 )

 var (

@@ -256,18 +256,7 @@ func (store *store) save() error {

 	if err != nil {

 		return err

 	}

-

-	tempFilePath := store.jsonPath + ".tmp"

-

-	if err := ioutil.WriteFile(tempFilePath, jsonData, 0600); err != nil {

-		return err

-	}

-

-	if err := os.Rename(tempFilePath, store.jsonPath); err != nil {

-		return err

-	}

-

-	return nil

+	return ioutils.AtomicWriteFile(store.jsonPath, jsonData, 0600)

 }

 func (store *store) reload() error {