Deprecate "devicemapper" storage driver, and add warning

The `devicemapper` storage driver is deprecated in favor of `overlay2`, and will
be removed in a future release. Users of the `devicemapper` storage driver are
recommended to migrate to a different storage driver, such as `overlay2`, which
is now the default storage driver.

The `devicemapper` storage driver facilitates running Docker on older (3.x) kernels
that have no support for other storage drivers (such as overlay2, or AUFS).

Now that support for `overlay2` is added to all supported distros (as they are
either on kernel 4.x, or have support for multiple lowerdirs backported), there
is no reason to continue maintenance of the `devicemapper` storage driver.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 06fcabbaa0d4f25db0580d3604bbed708223fb06)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/driver.go

@@ -195,6 +195,7 @@ type Options struct {
 func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, error) {
 	if name != "" {
 		logrus.Debugf("[graphdriver] trying provided driver: %s", name) // so the logs show specified driver
+		logDeprecatedWarning(name)
 		return GetDriver(name, pg, config)
 	}
 
@@ -232,6 +233,7 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err
 			}
 
 			logrus.Infof("[graphdriver] using prior storage driver: %s", name)
+			logDeprecatedWarning(name)
 			return driver, nil
 		}
 	}
@@ -245,6 +247,7 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err
 			}
 			return nil, err
 		}
+		logDeprecatedWarning(name)
 		return driver, nil
 	}
 
@@ -257,6 +260,7 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err
 			}
 			return nil, err
 		}
+		logDeprecatedWarning(name)
 		return driver, nil
 	}
 	return nil, fmt.Errorf("No supported storage backend found")
@@ -305,3 +309,20 @@ func isEmptyDir(name string) bool {
 	}
 	return false
 }
+
+// isDeprecated checks if a storage-driver is marked "deprecated"
+func isDeprecated(name string) bool {
+	switch name {
+	// NOTE: when deprecating a driver, update daemon.fillDriverInfo() accordingly
+	case "devicemapper":
+		return true
+	}
+	return false
+}
+
+// logDeprecatedWarning logs a warning if the given storage-driver is marked "deprecated"
+func logDeprecatedWarning(name string) {
+	if isDeprecated(name) {
+		logrus.Warnf("[graphdriver] WARNING: the %s storage-driver is deprecated, and will be removed in a future release", name)
+	}
+}

daemon/info.go

@@ -131,6 +131,10 @@ func (daemon *Daemon) fillDriverInfo(v *types.Info) {
 		if len(daemon.graphDrivers) > 1 {
 			drivers += fmt.Sprintf(" (%s) ", os)
 		}
+		switch gd {
+		case "devicemapper":
+			v.Warnings = append(v.Warnings, fmt.Sprintf("WARNING: the %s storage-driver is deprecated, and will be removed in a future release.", gd))
+		}
 	}
 	drivers = strings.TrimSpace(drivers)