Add support for volume scope + autodetection

Since Docker 1.12, volumes can report their scope as either "global"
or "local". Global scope means volumes are available on all nodes in
a Docker Swarm cluster (so Swarm should act accordingly, for example
it should not try to remove a global volume on each node).

By default (or when started with -scope auto), scope is autodetected,
meaning if driver's home is on Virtuozzo Storage, global scope is set
and reported, otherwise it's assumed as local. This can be overriden
from the command line ("-scope local" or "-scope global").

For more details, see moby/moby#22077

Signed-off-by: Kir Kolyshkin <[email protected]>

Makefile

@@ -1,4 +1,4 @@
-SOURCES = driver.go main.go paths.go vstorage.go
+SOURCES = driver.go main.go paths.go vstorage.go fstype.go
 WORKPLACE = $(abspath Godeps/_workspace)
 
 BIN = docker-volume-ploop

driver.go

@@ -29,10 +29,11 @@ import (
  */
 
 type volumeOptions struct {
-	size uint64          // ploop image size, in kilobytes
-	mode ploop.ImageMode // ploop image format (expanded/prealloc/raw)
-	clog uint            // cluster block log size in 512-byte sectors
-	tier int8            // Virtuozzo storage tier (-1: use default)
+	size  uint64          // ploop image size, in kilobytes
+	mode  ploop.ImageMode // ploop image format (expanded/prealloc/raw)
+	clog  uint            // cluster block log size in 512-byte sectors
+	tier  int8            // Virtuozzo storage tier (-1: use default)
+	scope string          // Volume scope (global/local/auto)
 }
 
 type mount struct {
@@ -87,6 +88,12 @@ func (o *volumeOptions) setTier(str string) error {
 	return nil
 }
 
+func (o *volumeOptions) setScope(str string) error {
+	// FIXME: check for local/global/auto?
+	o.scope = str
+	return nil
+}
+
 func newPloopDriver(home string, opts *volumeOptions) *ploopDriver {
 	// home must exist
 	_, err := os.Stat(home)
@@ -98,6 +105,16 @@ func newPloopDriver(home string, opts *volumeOptions) *ploopDriver {
 		}
 	}
 
+	// Autodetect scope: global if home is on vstorage, local otherwise
+	if opts.scope == "auto" {
+		if isOnVstorage(home) {
+			opts.scope = "global"
+		} else {
+			opts.scope = "local"
+		}
+		logrus.Infof("Autodetecting driver scope: %s", opts.scope)
+	}
+
 	d := ploopDriver{
 		home:   home,
 		opts:   *opts,
@@ -346,6 +363,11 @@ func (d *ploopDriver) Path(r volume.Request) volume.Response {
 	// TODO: check if mounted?
 	return volume.Response{Mountpoint: d.mnt(r.Name)}
 }
+func (d *ploopDriver) Capabilities(r volume.Request) volume.Response {
+	return volume.Response{
+		Capabilities: volume.Capability{
+			Scope: d.opts.scope}}
+}
 
 // Check if a given volume exist
 func (d *ploopDriver) volExist(name string) (bool, error) {

main.go

@@ -14,6 +14,7 @@ import (
 // Options and their default values
 var (
 	home  = flag.String("home", "/pcs", "Base directory where volumes are created")
+	scope = flag.String("scope", "auto", "Volumes scope (local or global)")
 	size  = flag.String("size", "16GB", "Default image size")
 	mode  = flag.String("mode", "expanded", "Default ploop image mode")
 	clog  = flag.String("clog", "0", "Cluster block log size in 512-byte sectors")
@@ -52,6 +53,9 @@ func main() {
 	if err := opts.setTier(*tier); err != nil {
 		logrus.Fatalf(err.Error())
 	}
+	if err := opts.setScope(*scope); err != nil {
+		logrus.Fatalf(err.Error())
+	}
 
 	// Set log level
 	if *debug {

vstorage.go

@@ -74,3 +74,14 @@ func vstorageSetTier(path string, tier int8) error {
 
 	return err
 }
+
+// Check if a file/directory is actually on vstorage
+func isOnVstorage(path string) bool {
+	fs, err := GetFilesystemType(path)
+	if err != nil {
+		logrus.Errorf("Can't figure %s fs: %v", err)
+		return false
+	}
+
+	return fs == "fuse.vstorage"
+}