Add support for volume scopes

This is similar to network scopes where a volume can either be `local`
or `global`. A `global` volume is one that exists across the entire
cluster where as a `local` volume exists on a single engine.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

daemon/daemon.go

@@ -745,7 +745,9 @@ func configureVolumes(config *Config, rootUID, rootGID int) (*store.VolumeStore,
 		return nil, err
 	}
 
-	volumedrivers.Register(volumesDriver, volumesDriver.Name())
+	if !volumedrivers.Register(volumesDriver, volumesDriver.Name()) {
+		return nil, fmt.Errorf("local volume driver could not be registered")
+	}
 	return store.New(config.Root)
 }
 

daemon/volumes.go

@@ -27,11 +27,13 @@ func volumeToAPIType(v volume.Volume) *types.Volume {
 		Name:   v.Name(),
 		Driver: v.DriverName(),
 	}
-	if v, ok := v.(interface {
-		Labels() map[string]string
-	}); ok {
+	if v, ok := v.(volume.LabeledVolume); ok {
 		tv.Labels = v.Labels()
 	}
+
+	if v, ok := v.(volume.ScopedVolume); ok {
+		tv.Scope = v.Scope()
+	}
 	return tv
 }
 

docs/extend/plugins_volume.md

@@ -20,6 +20,7 @@ documentation](plugins.md) for more information.
 ### 1.12.0
 
 - Add `Status` field to `VolumeDriver.Get` response ([#21006](https://github.com/docker/docker/pull/21006#))
+- Add `VolumeDriver.Capabilities` to get capabilities of the volume driver([#22077](https://github.com/docker/docker/pull/22077))
 
 ### 1.10.0
 
@@ -236,3 +237,29 @@ Get the list of volumes registered with the plugin.
 ```
 
 Respond with a string error if an error occurred.
+
+### /VolumeDriver.Capabilities
+
+**Request**:
+```json
+{}
+```
+
+Get the list of capabilities the driver supports.
+The driver is not required to implement this endpoint, however in such cases
+the default values will be taken.
+
+**Response**:
+```json
+{
+  "Capabilities": {
+    "Scope": "global"
+  }
+}
+```
+
+Supported scopes are `global` and `local`. Any other value in `Scope` will be
+ignored and assumed to be `local`. Scope allows cluster managers to handle the
+volume differently, for instance with a scope of `global`, the cluster manager
+knows it only needs to create the volume once instead of on every engine. More
+capabilities may be added in the future.

integration-cli/docker_cli_external_volume_driver_unix_test.go

@@ -16,6 +16,7 @@ import (
 	"time"
 
 	"github.com/docker/docker/pkg/integration/checker"
+	"github.com/docker/docker/volume"
 	"github.com/docker/engine-api/types"
 	"github.com/go-check/check"
 )
@@ -35,6 +36,7 @@ type eventCounter struct {
 	paths       int
 	lists       int
 	gets        int
+	caps        int
 }
 
 type DockerExternalVolumeSuite struct {
@@ -225,6 +227,18 @@ func (s *DockerExternalVolumeSuite) SetUpSuite(c *check.C) {
 		send(w, nil)
 	})
 
+	mux.HandleFunc("/VolumeDriver.Capabilities", func(w http.ResponseWriter, r *http.Request) {
+		s.ec.caps++
+
+		_, err := read(r.Body)
+		if err != nil {
+			send(w, err)
+			return
+		}
+
+		send(w, `{"Capabilities": { "Scope": "global" }}`)
+	})
+
 	err := os.MkdirAll("/etc/docker/plugins", 0755)
 	c.Assert(err, checker.IsNil)
 
@@ -491,3 +505,18 @@ func (s *DockerExternalVolumeSuite) TestExternalVolumeDriverMountID(c *check.C)
 	c.Assert(err, checker.IsNil, check.Commentf(out))
 	c.Assert(strings.TrimSpace(out), checker.Not(checker.Equals), "")
 }
+
+// Check that VolumeDriver.Capabilities gets called, and only called once
+func (s *DockerExternalVolumeSuite) TestExternalVolumeDriverCapabilities(c *check.C) {
+	c.Assert(s.d.Start(), checker.IsNil)
+	c.Assert(s.ec.caps, checker.Equals, 0)
+
+	for i := 0; i < 3; i++ {
+		out, err := s.d.Cmd("volume", "create", "-d", "test-external-volume-driver", "--name", fmt.Sprintf("test%d", i))
+		c.Assert(err, checker.IsNil, check.Commentf(out))
+		c.Assert(s.ec.caps, checker.Equals, 1)
+		out, err = s.d.Cmd("volume", "inspect", "--format={{.Scope}}", fmt.Sprintf("test%d", i))
+		c.Assert(err, checker.IsNil)
+		c.Assert(strings.TrimSpace(out), checker.Equals, volume.GlobalScope)
+	}
+}

pkg/plugins/pluginrpc-gen/main.go

@@ -78,7 +78,7 @@ func main() {
 
 	errorOut("parser error", generatedTempl.Execute(&buf, analysis))
 	src, err := format.Source(buf.Bytes())
-	errorOut("error formating generated source:\n"+buf.String(), err)
+	errorOut("error formatting generated source:\n"+buf.String(), err)
 	errorOut("error writing file", ioutil.WriteFile(*outputFile, src, 0644))
 }
 

volume/drivers/adapter.go

@@ -1,14 +1,22 @@
 package volumedrivers
 
 import (
-	"fmt"
+	"errors"
+	"strings"
 
+	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/volume"
 )
 
+var (
+	errInvalidScope = errors.New("invalid scope")
+	errNoSuchVolume = errors.New("no such volume")
+)
+
 type volumeDriverAdapter struct {
-	name  string
-	proxy *volumeDriverProxy
+	name         string
+	capabilities *volume.Capability
+	proxy        *volumeDriverProxy
 }
 
 func (a *volumeDriverAdapter) Name() string {
@@ -56,7 +64,7 @@ func (a *volumeDriverAdapter) Get(name string) (volume.Volume, error) {
 
 	// plugin may have returned no volume and no error
 	if v == nil {
-		return nil, fmt.Errorf("no such volume")
+		return nil, errNoSuchVolume
 	}
 
 	return &volumeAdapter{
@@ -68,6 +76,38 @@ func (a *volumeDriverAdapter) Get(name string) (volume.Volume, error) {
 	}, nil
 }
 
+func (a *volumeDriverAdapter) Scope() string {
+	cap := a.getCapabilities()
+	return cap.Scope
+}
+
+func (a *volumeDriverAdapter) getCapabilities() volume.Capability {
+	if a.capabilities != nil {
+		return *a.capabilities
+	}
+	cap, err := a.proxy.Capabilities()
+	if err != nil {
+		// `GetCapabilities` is a not a required endpoint.
+		// On error assume it's a local-only driver
+		logrus.Warnf("Volume driver %s returned an error while trying to query it's capabilities, using default capabilties: %v", a.name, err)
+		return volume.Capability{Scope: volume.LocalScope}
+	}
+
+	// don't spam the warn log below just because the plugin didn't provide a scope
+	if len(cap.Scope) == 0 {
+		cap.Scope = volume.LocalScope
+	}
+
+	cap.Scope = strings.ToLower(cap.Scope)
+	if cap.Scope != volume.LocalScope && cap.Scope != volume.GlobalScope {
+		logrus.Warnf("Volume driver %q returned an invalid scope: %q", a.Name(), cap.Scope)
+		cap.Scope = volume.LocalScope
+	}
+
+	a.capabilities = &cap
+	return cap
+}
+
 type volumeAdapter struct {
 	proxy      *volumeDriverProxy
 	name       string

volume/drivers/extpoint.go

@@ -42,6 +42,8 @@ type volumeDriver interface {
 	List() (volumes []*proxyVolume, err error)
 	// Get retrieves the volume with the requested name
 	Get(name string) (volume *proxyVolume, err error)
+	// Capabilities gets the list of capabilities of the driver
+	Capabilities() (capabilities volume.Capability, err error)
 }
 
 type driverExtpoint struct {
@@ -64,6 +66,11 @@ func Register(extension volume.Driver, name string) bool {
 	if exists {
 		return false
 	}
+
+	if err := validateDriver(extension); err != nil {
+		return false
+	}
+
 	drivers.extensions[name] = extension
 	return true
 }
@@ -107,10 +114,22 @@ func Lookup(name string) (volume.Driver, error) {
 	}
 
 	d := NewVolumeDriver(name, pl.Client)
+	if err := validateDriver(d); err != nil {
+		return nil, err
+	}
+
 	drivers.extensions[name] = d
 	return d, nil
 }
 
+func validateDriver(vd volume.Driver) error {
+	scope := vd.Scope()
+	if scope != volume.LocalScope && scope != volume.GlobalScope {
+		return fmt.Errorf("Driver %q provided an invalid capability scope: %s", vd.Name(), scope)
+	}
+	return nil
+}
+
 // GetDriver returns a volume driver by its name.
 // If the driver is empty, it looks for the local driver.
 func GetDriver(name string) (volume.Driver, error) {

volume/drivers/proxy.go

@@ -2,7 +2,10 @@
 
 package volumedrivers
 
-import "errors"
+import (
+	"errors"
+	"github.com/docker/docker/volume"
+)
 
 type client interface {
 	Call(string, interface{}, interface{}) error
@@ -209,3 +212,30 @@ func (pp *volumeDriverProxy) Get(name string) (volume *proxyVolume, err error) {
 
 	return
 }
+
+type volumeDriverProxyCapabilitiesRequest struct {
+}
+
+type volumeDriverProxyCapabilitiesResponse struct {
+	Capabilities volume.Capability
+	Err          string
+}
+
+func (pp *volumeDriverProxy) Capabilities() (capabilities volume.Capability, err error) {
+	var (
+		req volumeDriverProxyCapabilitiesRequest
+		ret volumeDriverProxyCapabilitiesResponse
+	)
+
+	if err = pp.Call("VolumeDriver.Capabilities", req, &ret); err != nil {
+		return
+	}
+
+	capabilities = ret.Capabilities
+
+	if ret.Err != "" {
+		err = errors.New(ret.Err)
+	}
+
+	return
+}

volume/drivers/proxy_test.go

@@ -52,6 +52,11 @@ func TestVolumeRequestError(t *testing.T) {
 		fmt.Fprintln(w, `{"Err": "Cannot get volume"}`)
 	})
 
+	mux.HandleFunc("/VolumeDriver.Capabilities", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/vnd.docker.plugins.v1+json")
+		http.Error(w, "error", 500)
+	})
+
 	u, _ := url.Parse(server.URL)
 	client, err := plugins.NewClient("tcp://"+u.Host, tlsconfig.Options{InsecureSkipVerify: true})
 	if err != nil {
@@ -119,4 +124,9 @@ func TestVolumeRequestError(t *testing.T) {
 	if !strings.Contains(err.Error(), "Cannot get volume") {
 		t.Fatalf("Unexpected error: %v\n", err)
 	}
+
+	_, err = driver.Capabilities()
+	if err == nil {
+		t.Fatal(err)
+	}
 }

volume/local/local.go

@@ -248,6 +248,11 @@ func (r *Root) Get(name string) (volume.Volume, error) {
 	return v, nil
 }
 
+// Scope returns the local volume scope
+func (r *Root) Scope() string {
+	return volume.LocalScope
+}
+
 func (r *Root) validateName(name string) error {
 	if !volumeNameRegex.MatchString(name) {
 		return validationError{fmt.Errorf("%q includes invalid characters for a local volume name, only %q are allowed", name, utils.RestrictedNameChars)}

volume/store/store.go

@@ -25,15 +25,29 @@ type volumeMetadata struct {
 	Labels map[string]string
 }
 
-type volumeWithLabels struct {
+type volumeWrapper struct {
 	volume.Volume
 	labels map[string]string
+	scope  string
 }
 
-func (v volumeWithLabels) Labels() map[string]string {
+func (v volumeWrapper) Labels() map[string]string {
 	return v.labels
 }
 
+func (v volumeWrapper) Scope() string {
+	return v.scope
+}
+
+func (v volumeWrapper) CachedPath() string {
+	if vv, ok := v.Volume.(interface {
+		CachedPath() string
+	}); ok {
+		return vv.CachedPath()
+	}
+	return v.Volume.Path()
+}
+
 // New initializes a VolumeStore to keep
 // reference counting of volumes in the system.
 func New(rootPath string) (*VolumeStore, error) {
@@ -166,6 +180,10 @@ func (s *VolumeStore) list() ([]volume.Volume, []string, error) {
 				chVols <- vols{driverName: d.Name(), err: &OpErr{Err: err, Name: d.Name(), Op: "list"}}
 				return
 			}
+			for i, v := range vs {
+				vs[i] = volumeWrapper{v, s.labels[v.Name()], d.Scope()}
+			}
+
 			chVols <- vols{vols: vs}
 		}(vd)
 	}
@@ -291,7 +309,7 @@ func (s *VolumeStore) create(name, driverName string, opts, labels map[string]st
 		}
 	}
 
-	return volumeWithLabels{v, labels}, nil
+	return volumeWrapper{v, labels, vd.Scope()}, nil
 }
 
 // GetWithRef gets a volume with the given name from the passed in driver and stores the ref
@@ -313,10 +331,8 @@ func (s *VolumeStore) GetWithRef(name, driverName, ref string) (volume.Volume, e
 	}
 
 	s.setNamed(v, ref)
-	if labels, ok := s.labels[name]; ok {
-		return volumeWithLabels{v, labels}, nil
-	}
-	return v, nil
+
+	return volumeWrapper{v, s.labels[name], vd.Scope()}, nil
 }
 
 // Get looks if a volume with the given name exists and returns it if so
@@ -376,7 +392,7 @@ func (s *VolumeStore) getVolume(name string) (volume.Volume, error) {
 		if err != nil {
 			return nil, err
 		}
-		return volumeWithLabels{vol, labels}, nil
+		return volumeWrapper{vol, labels, vd.Scope()}, nil
 	}
 
 	logrus.Debugf("Probing all drivers for volume with name: %s", name)
@@ -391,7 +407,7 @@ func (s *VolumeStore) getVolume(name string) (volume.Volume, error) {
 			continue
 		}
 
-		return volumeWithLabels{v, labels}, nil
+		return volumeWrapper{v, labels, d.Scope()}, nil
 	}
 	return nil, errNoSuchVolume
 }
@@ -412,7 +428,7 @@ func (s *VolumeStore) Remove(v volume.Volume) error {
 	}
 
 	logrus.Debugf("Removing volume reference: driver %s, name %s", v.DriverName(), name)
-	vol := withoutLabels(v)
+	vol := unwrapVolume(v)
 	if err := vd.Remove(vol); err != nil {
 		return &OpErr{Err: err, Name: name, Op: "remove"}
 	}
@@ -465,6 +481,9 @@ func (s *VolumeStore) FilterByDriver(name string) ([]volume.Volume, error) {
 	if err != nil {
 		return nil, &OpErr{Err: err, Name: name, Op: "list"}
 	}
+	for i, v := range ls {
+		ls[i] = volumeWrapper{v, s.labels[v.Name()], vd.Scope()}
+	}
 	return ls, nil
 }
 
@@ -497,8 +516,8 @@ func (s *VolumeStore) filter(vols []volume.Volume, f filterFunc) []volume.Volume
 	return ls
 }
 
-func withoutLabels(v volume.Volume) volume.Volume {
-	if vol, ok := v.(volumeWithLabels); ok {
+func unwrapVolume(v volume.Volume) volume.Volume {
+	if vol, ok := v.(volumeWrapper); ok {
 		return vol.Volume
 	}
 

volume/testutils/testutils.go

@@ -109,3 +109,8 @@ func (d *FakeDriver) Get(name string) (volume.Volume, error) {
 	}
 	return nil, fmt.Errorf("no such volume")
 }
+
+// Scope returns the local scope
+func (*FakeDriver) Scope() string {
+	return "local"
+}

volume/volume.go

@@ -13,7 +13,14 @@ import (
 
 // DefaultDriverName is the driver name used for the driver
 // implemented in the local package.
-const DefaultDriverName string = "local"
+const DefaultDriverName = "local"
+
+// Scopes define if a volume has is cluster-wide (global) or local only.
+// Scopes are returned by the volume driver when it is queried for capabilities and then set on a volume
+const (
+	LocalScope  = "local"
+	GlobalScope = "global"
+)
 
 // Driver is for creating and removing volumes.
 type Driver interface {
@@ -27,6 +34,18 @@ type Driver interface {
 	List() ([]Volume, error)
 	// Get retrieves the volume with the requested name
 	Get(name string) (Volume, error)
+	// Scope returns the scope of the driver (e.g. `golbal` or `local`).
+	// Scope determines how the driver is handled at a cluster level
+	Scope() string
+}
+
+// Capability defines a set of capabilities that a driver is able to handle.
+type Capability struct {
+	// Scope is the scope of the driver, `global` or `local`
+	// A `global` scope indicates that the driver manages volumes across the cluster
+	// A `local` scope indicates that the driver only manages volumes resources local to the host
+	// Scope is declared by the driver
+	Scope string
 }
 
 // Volume is a place to store data. It is backed by a specific driver, and can be mounted.
@@ -46,6 +65,18 @@ type Volume interface {
 	Status() map[string]interface{}
 }
 
+// LabeledVolume wraps a Volume with user-defined labels
+type LabeledVolume interface {
+	Labels() map[string]string
+	Volume
+}
+
+// ScopedVolume wraps a volume with a cluster scope (e.g., `local` or `global`)
+type ScopedVolume interface {
+	Scope() string
+	Volume
+}
+
 // MountPoint is the intersection point between a volume and a container. It
 // specifies which volume is to be used and where inside a container it should
 // be mounted.