new file mode 100644

@@ -0,0 +1,32 @@

+package graphdriver

+

+import "sync"

+

+// RefCounter is a generic counter for use by graphdriver Get/Put calls

+type RefCounter struct {

+	counts map[string]int

+	mu     sync.Mutex

+}

+

+// NewRefCounter returns a new RefCounter

+func NewRefCounter() *RefCounter {

+	return &RefCounter{counts: make(map[string]int)}

+}

+

+// Increment increaes the ref count for the given id and returns the current count

+func (c *RefCounter) Increment(id string) int {

+	c.mu.Lock()

+	c.counts[id]++

+	count := c.counts[id]

+	c.mu.Unlock()

+	return count

+}

+

+// Decrement decreases the ref count for the given id and returns the current count

+func (c *RefCounter) Decrement(id string) int {

+	c.mu.Lock()

+	c.counts[id]--

+	count := c.counts[id]

+	c.mu.Unlock()

+	return count

+}

@@ -28,6 +28,7 @@ type Driver struct {

 	home    string

 	uidMaps []idtools.IDMap

 	gidMaps []idtools.IDMap

+	ctr     *graphdriver.RefCounter

 }

 // Init creates a driver with the given home and the set of options.

@@ -46,6 +47,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		home:      home,

 		uidMaps:   uidMaps,

 		gidMaps:   gidMaps,

+		ctr:       graphdriver.NewRefCounter(),

 	}

 	return graphdriver.NewNaiveDiffDriver(d, uidMaps, gidMaps), nil

@@ -151,26 +153,35 @@ func (d *Driver) Remove(id string) error {

 // Get mounts a device with given id into the root filesystem

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

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

+	if count := d.ctr.Increment(id); count > 1 {

+		return mp, nil

+	}

 	uid, gid, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)

 	if err != nil {

+		d.ctr.Decrement(id)

 		return "", err

 	}

+

 	// Create the target directories if they don't exist

 	if err := idtools.MkdirAllAs(path.Join(d.home, "mnt"), 0755, uid, gid); err != nil && !os.IsExist(err) {

+		d.ctr.Decrement(id)

 		return "", err

 	}

 	if err := idtools.MkdirAs(mp, 0755, uid, gid); err != nil && !os.IsExist(err) {

+		d.ctr.Decrement(id)

 		return "", err

 	}

 	// Mount the device

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

+		d.ctr.Decrement(id)

 		return "", err

 	}

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

 	if err := idtools.MkdirAllAs(rootFs, 0755, uid, gid); err != nil && !os.IsExist(err) {

+		d.ctr.Decrement(id)

 		d.DeviceSet.UnmountDevice(id, mp)

 		return "", err

 	}

@@ -180,6 +191,7 @@ func (d *Driver) Get(id, mountLabel string) (string, error) {

 		// Create an "id" file with the container/image id in it to help reconstruct this in case

 		// of later problems

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

+			d.ctr.Decrement(id)

 			d.DeviceSet.UnmountDevice(id, mp)

 			return "", err

 		}

@@ -190,6 +202,9 @@ func (d *Driver) Get(id, mountLabel string) (string, error) {

 // Put unmounts a device and removes it.

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

+	if count := d.ctr.Decrement(id); count > 0 {

+		return nil

+	}

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

 	err := d.DeviceSet.UnmountDevice(id, mp)

 	if err != nil {

@@ -95,6 +95,7 @@ type Driver struct {

 	pathCache     map[string]string

 	uidMaps       []idtools.IDMap

 	gidMaps       []idtools.IDMap

+	ctr           *graphdriver.RefCounter

 }

 var backingFs = "<unknown>"

@@ -147,6 +148,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		pathCache: make(map[string]string),

 		uidMaps:   uidMaps,

 		gidMaps:   gidMaps,

+		ctr:       graphdriver.NewRefCounter(),

 	}

 	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil

@@ -348,28 +350,39 @@ func (d *Driver) Get(id string, mountLabel string) (string, error) {

 	workDir := path.Join(dir, "work")

 	mergedDir := path.Join(dir, "merged")

+	if count := d.ctr.Increment(id); count > 1 {

+		return mergedDir, nil

+	}

+

 	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, upperDir, workDir)

 	// if it's mounted already, just return

 	mounted, err := d.mounted(mergedDir)

 	if err != nil {

+		d.ctr.Decrement(id)

 		return "", err

 	}

 	if mounted {

+		d.ctr.Decrement(id)

 		return mergedDir, nil

 	}

 	if err := syscall.Mount("overlay", mergedDir, "overlay", 0, label.FormatMountLabel(opts, mountLabel)); err != nil {

+		d.ctr.Decrement(id)

 		return "", fmt.Errorf("error creating overlay mount to %s: %v", mergedDir, err)

 	}

 	// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a

 	// user namespace requires this to move a directory from lower to upper.

 	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)

 	if err != nil {

+		d.ctr.Decrement(id)

+		syscall.Unmount(mergedDir, 0)

 		return "", err

 	}

 	if err := os.Chown(path.Join(workDir, "work"), rootUID, rootGID); err != nil {

+		d.ctr.Decrement(id)

+		syscall.Unmount(mergedDir, 0)

 		return "", err

 	}

@@ -386,6 +399,9 @@ func (d *Driver) mounted(dir string) (bool, error) {

 // Put unmounts the mount path created for the give id.

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

+	if count := d.ctr.Decrement(id); count > 0 {

+		return nil

+	}

 	d.pathCacheLock.Lock()

 	mountpoint, exists := d.pathCache[id]

 	d.pathCacheLock.Unlock()

@@ -105,6 +105,7 @@ func Init(base string, opt []string, uidMaps, gidMaps []idtools.IDMap) (graphdri

 		filesystemsCache: filesystemsCache,

 		uidMaps:          uidMaps,

 		gidMaps:          gidMaps,

+		ctr:              graphdriver.NewRefCounter(),

 	}

 	return graphdriver.NewNaiveDiffDriver(d, uidMaps, gidMaps), nil

 }

@@ -161,6 +162,7 @@ type Driver struct {

 	filesystemsCache map[string]bool

 	uidMaps          []idtools.IDMap

 	gidMaps          []idtools.IDMap

+	ctr              *graphdriver.RefCounter

 }

 func (d *Driver) String() string {

@@ -295,25 +297,35 @@ func (d *Driver) Remove(id string) error {

 // Get returns the mountpoint for the given id after creating the target directories if necessary.

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

 	mountpoint := d.mountPath(id)

+	if count := d.ctr.Increment(id); count > 1 {

+		return mountpoint, nil

+	}

+

 	filesystem := d.zfsPath(id)

 	options := label.FormatMountLabel("", mountLabel)

 	logrus.Debugf(`[zfs] mount("%s", "%s", "%s")`, filesystem, mountpoint, options)

 	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)

 	if err != nil {

+		d.ctr.Decrement(id)

 		return "", err

 	}

 	// Create the target directories if they don't exist

 	if err := idtools.MkdirAllAs(mountpoint, 0755, rootUID, rootGID); err != nil {

+		d.ctr.Decrement(id)

 		return "", err

 	}

 	if err := mount.Mount(filesystem, mountpoint, "zfs", options); err != nil {

+		d.ctr.Decrement(id)

 		return "", fmt.Errorf("error creating zfs mount of %s to %s: %v", filesystem, mountpoint, err)

 	}

+

 	// this could be our first mount after creation of the filesystem, and the root dir may still have root

 	// permissions instead of the remapped root uid:gid (if user namespaces are enabled):

 	if err := os.Chown(mountpoint, rootUID, rootGID); err != nil {

+		mount.Unmount(mountpoint)

+		d.ctr.Decrement(id)

 		return "", fmt.Errorf("error modifying zfs mountpoint (%s) directory ownership: %v", mountpoint, err)

 	}

@@ -322,6 +334,9 @@ func (d *Driver) Get(id, mountLabel string) (string, error) {

 // Put removes the existing mountpoint for the given id if it exists.

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

+	if count := d.ctr.Decrement(id); count > 0 {

+		return nil

+	}

 	mountpoint := d.mountPath(id)

 	mounted, err := graphdriver.Mounted(graphdriver.FsMagicZfs, mountpoint)

 	if err != nil || !mounted {