overlay: do not ignore invalid storage-driver options

The overlay storage driver currently does not support any option, but was silently
ignoring any option that was passed.

This patch verifies that no options are passed, and if they are passed will produce
an error.

Before this change:

    dockerd --storage-driver=overlay --storage-opt dm.thinp_percent=95
    INFO[2018-05-11T11:40:40.996597152Z] libcontainerd: started new docker-containerd process  pid=256
    ....
    INFO[2018-05-11T11:40:41.135392535Z] Daemon has completed initialization
    INFO[2018-05-11T11:40:41.141035093Z] API listen on /var/run/docker.sock

After this change:

    dockerd --storage-driver=overlay --storage-opt dm.thinp_percent=95
    INFO[2018-05-11T11:39:21.632610319Z] libcontainerd: started new docker-containerd process  pid=233
    ....
    Error starting daemon: error initializing graphdriver: overlay: unknown option dm.thinp_percent

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/overlay/overlay.go

@@ -12,6 +12,7 @@ import (
 	"path"
 	"path/filepath"
 	"strconv"
+	"strings"
 
 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/docker/docker/daemon/graphdriver/copy"
@@ -22,6 +23,7 @@ import (
 	"github.com/docker/docker/pkg/idtools"
 	"github.com/docker/docker/pkg/locker"
 	"github.com/docker/docker/pkg/mount"
+	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/docker/pkg/system"
 	"github.com/opencontainers/selinux/go-selinux/label"
 	"github.com/sirupsen/logrus"
@@ -95,6 +97,8 @@ func (d *naiveDiffDriverWithApply) ApplyDiff(id, parent string, diff io.Reader)
 // of that. This means all child images share file (but not directory)
 // data with the parent.
 
+type overlayOptions struct{}
+
 // Driver contains information about the home directory and the list of active mounts that are created using this driver.
 type Driver struct {
 	home          string
@@ -115,6 +119,10 @@ func init() {
 // If an overlay filesystem is not supported over an existing filesystem then
 // error graphdriver.ErrIncompatibleFS is returned.
 func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
+	_, err := parseOptions(options)
+	if err != nil {
+		return nil, err
+	}
 
 	if err := supportsOverlay(); err != nil {
 		return nil, graphdriver.ErrNotSupported
@@ -176,6 +184,22 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil
 }
 
+func parseOptions(options []string) (*overlayOptions, error) {
+	o := &overlayOptions{}
+	for _, option := range options {
+		key, _, err := parsers.ParseKeyValueOpt(option)
+		if err != nil {
+			return nil, err
+		}
+		key = strings.ToLower(key)
+		switch key {
+		default:
+			return nil, fmt.Errorf("overlay: unknown option %s", key)
+		}
+	}
+	return o, nil
+}
+
 func supportsOverlay() error {
 	// We can try to modprobe overlay first before looking at
 	// proc/filesystems for when overlay is supported