lxc: Add config flag to disable volume support

Signed-off-by: Michael McCracken <mikmccra@cisco.com>

client/driver/lxc.go

@@ -31,6 +31,11 @@ const (
 	// Config.Options map.
 	lxcConfigOption = "driver.lxc.enable"
 
+	// lxcVolumesConfigOption is the key for enabling the use of
+	// custom bind volumes to arbitrary host paths
+	lxcVolumesConfigOption  = "lxc.volumes.enabled"
+	lxcVolumesConfigDefault = true
+
 	// containerMonitorIntv is the interval at which the driver checks if the
 	// container is still alive
 	containerMonitorIntv = 2 * time.Second
@@ -190,6 +195,12 @@ func (d *LxcDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool, e
 	}
 	node.Attributes["driver.lxc.version"] = version
 	node.Attributes["driver.lxc"] = "1"
+
+	// Advertise if this node supports lxc volumes
+	if d.config.ReadBoolDefault(lxcVolumesConfigOption, lxcVolumesConfigDefault) {
+		node.Attributes["driver."+lxcVolumesConfigOption] = "1"
+	}
+
 	return true, nil
 }
 
@@ -271,9 +282,21 @@ func (d *LxcDriver) Start(ctx *ExecContext, task *structs.Task) (*StartResponse,
 		fmt.Sprintf("%s secrets none rw,bind,create=dir", ctx.TaskDir.SecretsDir),
 	}
 
+	volumesEnabled := d.config.ReadBoolDefault(lxcVolumesConfigOption, lxcVolumesConfigDefault)
+
 	for _, volDesc := range driverConfig.Volumes {
 		// the format was checked in Validate()
 		paths := strings.Split(volDesc, ":")
+
+		if filepath.IsAbs(paths[0]) {
+			if !volumesEnabled {
+				return nil, fmt.Errorf("absolute bind-mount volume in config but '%v' is false", lxcVolumesConfigOption)
+			}
+		} else {
+			// Relative source paths are treated as relative to alloc dir
+			paths[0] = filepath.Join(ctx.TaskDir.Dir, paths[0])
+		}
+
 		mounts = append(mounts, fmt.Sprintf("%s %s none rw,bind,create=dir", paths[0], paths[1]))
 	}